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Study of the Aerosol Formation from the Mixture of Isoprene and Dimethyl Sulfide in the Presence of NOx

Permanent Link: http://ufdc.ufl.edu/UFE0044543/00001

Material Information

Title: Study of the Aerosol Formation from the Mixture of Isoprene and Dimethyl Sulfide in the Presence of NOx
Physical Description: 1 online resource (148 p.)
Language: english
Creator: Chen, Tianyi
Publisher: University of Florida
Place of Publication: Gainesville, Fla.
Publication Date: 2012

Subjects

Subjects / Keywords: dms -- h2so4 -- isoprene -- msa -- photooxidation -- soa
Environmental Engineering Sciences -- Dissertations, Academic -- UF
Genre: Environmental Engineering Sciences thesis, Ph.D.
bibliography   ( marcgt )
theses   ( marcgt )
government publication (state, provincial, terriorial, dependent)   ( marcgt )
born-digital   ( sobekcm )
Electronic Thesis or Dissertation

Notes

Abstract: Past and current research findings suggestthat the acid catalyzed heterogeneous reaction theory narrows the gap betweenthe ambient secondary organic aerosol (SOA) data and the predicted SOA data usingthe precursor flux multipliedby the SOA yield determined from chamber experiments. In this study, a reduced sulfur compound that is predominantly from oceanicsources, dimethyl sulfide (DMS), was proposed to be an additional source of aerosol acidity. SOA created from the photooxidation of a mixture of isoprene and DMS wasstudied using a Teflon film indoor chamber and for different NOxconcentrations (40 to 220 ppb) and relative humidity values of 12%, 42% and80%. Resultsobtained from chamber experiments showedthat the isoprene SOA yield is increased by 30% to 150% in the presenceof DMS. The impactof MSA on the SOA formation produced from photooxidation of isoprene in thepresence of NOx was investigated in a 2 m3 Teflon filmindoor chamber. Our study showed that MSA aerosol can significantly increasethe isoprene SOA. In order to model the SOA formation in the presence of MSAand H2SO4, a prediction model of DMS photooxidation wasdeveloped. The most recently reported reactionswith their rate constants have been included. The model included in this studypredicted that concentrations of both MSA and H2SO4 wouldsignificantly increase due to heterogeneous chemistry, and this was wellsubstantiated with experimental data. To confirm the DMS effect on SOAformation in the ambient air, the effect of MSA on increasing the SOA mass and therelative contribution of SO2 and DMS to sulfate were evaluatedthrough ambient aerosol samples. Our results suggest that DMS is a significantsource of acidic aerosol (H2SO4 and MSA) in the coastalarea and in the land surrounded by fresh water wetland or salt marsh.
General Note: In the series University of Florida Digital Collections.
General Note: Includes vita.
Bibliography: Includes bibliographical references.
Source of Description: Description based on online resource; title from PDF title page.
Source of Description: This bibliographic record is available under the Creative Commons CC0 public domain dedication. The University of Florida Libraries, as creator of this bibliographic record, has waived all rights to it worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law.
Statement of Responsibility: by Tianyi Chen.
Thesis: Thesis (Ph.D.)--University of Florida, 2012.
Local: Adviser: Jang, Myoseon.

Record Information

Source Institution: UFRGP
Rights Management: Applicable rights reserved.
Classification: lcc - LD1780 2012
System ID: UFE0044543:00001

Permanent Link: http://ufdc.ufl.edu/UFE0044543/00001

Material Information

Title: Study of the Aerosol Formation from the Mixture of Isoprene and Dimethyl Sulfide in the Presence of NOx
Physical Description: 1 online resource (148 p.)
Language: english
Creator: Chen, Tianyi
Publisher: University of Florida
Place of Publication: Gainesville, Fla.
Publication Date: 2012

Subjects

Subjects / Keywords: dms -- h2so4 -- isoprene -- msa -- photooxidation -- soa
Environmental Engineering Sciences -- Dissertations, Academic -- UF
Genre: Environmental Engineering Sciences thesis, Ph.D.
bibliography   ( marcgt )
theses   ( marcgt )
government publication (state, provincial, terriorial, dependent)   ( marcgt )
born-digital   ( sobekcm )
Electronic Thesis or Dissertation

Notes

Abstract: Past and current research findings suggestthat the acid catalyzed heterogeneous reaction theory narrows the gap betweenthe ambient secondary organic aerosol (SOA) data and the predicted SOA data usingthe precursor flux multipliedby the SOA yield determined from chamber experiments. In this study, a reduced sulfur compound that is predominantly from oceanicsources, dimethyl sulfide (DMS), was proposed to be an additional source of aerosol acidity. SOA created from the photooxidation of a mixture of isoprene and DMS wasstudied using a Teflon film indoor chamber and for different NOxconcentrations (40 to 220 ppb) and relative humidity values of 12%, 42% and80%. Resultsobtained from chamber experiments showedthat the isoprene SOA yield is increased by 30% to 150% in the presenceof DMS. The impactof MSA on the SOA formation produced from photooxidation of isoprene in thepresence of NOx was investigated in a 2 m3 Teflon filmindoor chamber. Our study showed that MSA aerosol can significantly increasethe isoprene SOA. In order to model the SOA formation in the presence of MSAand H2SO4, a prediction model of DMS photooxidation wasdeveloped. The most recently reported reactionswith their rate constants have been included. The model included in this studypredicted that concentrations of both MSA and H2SO4 wouldsignificantly increase due to heterogeneous chemistry, and this was wellsubstantiated with experimental data. To confirm the DMS effect on SOAformation in the ambient air, the effect of MSA on increasing the SOA mass and therelative contribution of SO2 and DMS to sulfate were evaluatedthrough ambient aerosol samples. Our results suggest that DMS is a significantsource of acidic aerosol (H2SO4 and MSA) in the coastalarea and in the land surrounded by fresh water wetland or salt marsh.
General Note: In the series University of Florida Digital Collections.
General Note: Includes vita.
Bibliography: Includes bibliographical references.
Source of Description: Description based on online resource; title from PDF title page.
Source of Description: This bibliographic record is available under the Creative Commons CC0 public domain dedication. The University of Florida Libraries, as creator of this bibliographic record, has waived all rights to it worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law.
Statement of Responsibility: by Tianyi Chen.
Thesis: Thesis (Ph.D.)--University of Florida, 2012.
Local: Adviser: Jang, Myoseon.

Record Information

Source Institution: UFRGP
Rights Management: Applicable rights reserved.
Classification: lcc - LD1780 2012
System ID: UFE0044543:00001


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1 STUDY OF THE AEROSOL FORMATION FROM THE MIXTURE OF ISOPRENE AND DIMETHYL SULFIDE IN THE PRESENCE OF NO X By TIANYI CHEN A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE R EQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY UNIVERSITY OF FLORIDA 2012

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2 2012 Tianyi Chen

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3 To my beloved parents

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4 ACKNOWLEDGMENTS This work was supported by grants from the National Science Foundation (ATM 0852747) and the Alumni Scholarship from the University of Florida I would like to first thank my advisor, Dr. Myoseon Jang, for providing me with such an excellent research topic, offering me countless help in research and writing. Besides, I would like to thank Dr. Kevin Powe rs, Rick Yost and Jean Claude Bonzongo for being my committee members and giving me valuable comments in the research. Next, I would like to thank all my current and past lab mates. PhD study is tough, but working with you made me always positive toward m y research and I enjoyed every moment we spent these years. Finally, I want to thank my dad who is in China, for spiritual support these years and also my mother, who is right now in the heaven, for encouraging me to challenge the Ph D degree in the United States.

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5 TABLE OF CONTENTS page ACKNOWLEDGMENTS ................................ ................................ ................................ .. 4 LIST OF TABLES ................................ ................................ ................................ ............ 8 LIST OF FIGURES ................................ ................................ ................................ ........ 10 LIST OF ABBREVIATIONS ................................ ................................ ........................... 13 ABSTRACT ................................ ................................ ................................ ................... 14 CHAPTER 1 INTRODUCTION ................................ ................................ ................................ .... 16 Atmospheric A erosol and Secondary Organic Aerosol (SOA) ................................ 16 SOA Yield and Acid Catalyzed Heterogeneous Reactions ................................ ..... 17 SOA Yield ................................ ................................ ................................ ......... 17 Acid Catalyzed Heterogeneous Reactions ................................ ....................... 18 Dimethyl S ulfide, A M issing A cidic S ource ................................ ....................... 19 DMS Chemistry ................................ ................................ ................................ ....... 20 DMS E ffect on SOA in A mbient A ir ................................ ................................ ......... 21 2 SECONDARY ORGANIC AEROSOL FORMATI ON FROM PHOTOOXIDATION OF A MIXTURE OF DIMETHYL SULFIDE AND ISOPRENE ................................ 23 Background ................................ ................................ ................................ ............. 23 Experimental Section ................................ ................................ .............................. 26 Teflon Film Indoor Chamber Experiments ................................ ........................ 26 Chemicals and instruments. ................................ ................................ ............. 26 Results and Discussion ................................ ................................ ........................... 27 PILS IC D ata to S tudy the I mpact of I soprene on DMS A erosol F ormation ...... 27 OC A nalysis to S tudy the I mpact of DMS on I soprene SOA Y ields .................. 29 Comparison of PILS IC and OC D ata ................................ ............................... 33 The I mpact of DMS on the I soprene S OA Y ield: NO x E ffects ........................... 33 The I mpact of DMS on I soprene SOA F ormation: RH E ffects .......................... 34 The I mpact of DMS on I soprene SOA F ormation: A erosol G rowth P attern ...... 35 Uncertainties ................................ ................................ ................................ ........... 36 Atmospheric I mplications ................................ ................................ ........................ 36 3 STUDY OF THE EFFECT OF METHANESULFONIC ACID ON ISOPRENE SECONDA RY ORGANIC AEROSOL FORMATION ................................ ............... 47 Background ................................ ................................ ................................ ............. 47 Experimental Section ................................ ................................ .............................. 49

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6 Cha mber Experiments to Study the Impact of MSA on Isoprene SOA mass ... 49 Chamber Experiment Procedure in Figure 3 1A ................................ ........ 49 Aerosol Water Conte nt ................................ ................................ ............... 50 Characterization of Isoprene SOA Products (Figure 3 1B and 3 1C) ............... 50 Generation and S ampling of I soprene SOA ................................ ............... 50 Analytical P rocedure for I soprene SOA P roduct C haracterization ............. 51 Results and Discussion ................................ ................................ ........................... 52 SOA Yield Increase in the Presence of MSA Aerosol ................................ ...... 52 Product A nalysis on the I soprene SOA with and without MSA U sing GC ITMS. ................................ ................................ ................................ ............ 54 Con clusion and Atmospheric Implication ................................ ................................ 56 4 CHAMBER SIMULATION OF PHOTOOXIDATION OF DIMETHYL SULFIDE AND ISOPRENE IN THE PRESENCE OF NO X ................................ ..................... 66 Background ................................ ................................ ................................ ............. 66 Experimental Section ................................ ................................ .............................. 68 Indoor Teflon film Chamber Experiments of DMS O and DMS P hotooxidation ................................ ................................ .............................. 68 Experiment P rocedures ................................ ................................ ............. 68 Instrumentation and Sample Analysis ................................ ........................ 69 Indoor Teflon film Chamber Ex periments of DMS photooxidation in the P resence of I soprene ................................ ................................ .................... 70 Results and Discussion ................................ ................................ ........................... 70 Kinetic Model ................................ ................................ ................................ .... 70 Reaction m echanisms of DMS ................................ ................................ ... 70 Formation of MSA and H 2 SO 4 through heterogeneous reactions of gaseous DMS oxidation products ................................ ........................... 71 Isoprene oxidation mechanism ................................ ................................ .. 72 DMS M odel S imulation ................................ ................................ ..................... 72 Chamber c haracterization ................................ ................................ .......... 72 DMSO photooxidation ................................ ................................ ................ 73 DMS photooxidation ................................ ................................ ................... 74 Impact of the C oexisting I soprene on DMS P hotooxidati on .............................. 75 Isoprene p hotooxidation ................................ ................................ ............. 75 DMS p hotooxidation with c oexisting i soprene ................................ ............ 76 Potential Application of the Kinetic Model in Ambient Simulation ..................... 78 Conclusion and Atmospheric Implication ................................ ................................ 78 5 DOES DIMETHYL S ULFIDE AFFECT SECONDARY ORGANIC AEROSOL PRODUCTION IN AMBIENT PM 2.5 ? ................................ ................................ ....... 88 Background ................................ ................................ ................................ ............. 88 Experimental section ................................ ................................ ............................... 88 Sampling S ites ................................ ................................ ................................ 88 Sampling and S ample P reparation ................................ ................................ ... 89 Analytical M ethods ................................ ................................ ........................... 90

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7 Organic C ompounds A nalyses ................................ ................................ ... 90 Organic C arbon A nalysis ................................ ................................ ........... 90 Inorganic I on A nalyses ................................ ................................ ............... 91 Results and Discussion ................................ ................................ ........................... 91 Correlation of the A cids (NO 3 nss SO 4 2 and MS ) and O rganics (2 methyltetrol and OC sec ) ................................ ................................ ................. 91 Winter ................................ ................................ ................................ ........ 91 Spring and summer ................................ ................................ .................... 92 Source of MSA ................................ ................................ ................................ 93 The C ontribution of nss SO 4 (DMS_SO 4 2 ) from DMS P hotooxidation to the T otal SO 4 2 (SO 4 2 T ) ................................ ................................ ...................... 94 Conclusions and Atmospheric Implications ................................ ............................. 97 6 CONCLUSIONS ................................ ................................ ................................ ... 106 7 FUTURE STUDIES ................................ ................................ ............................... 108 APPENDIX A SUPPLEME N TARY MATERIALS FOR CHAPTER 4 ................................ ........... 110 B SUPPLEME N TARY MATERIALS FOR CHAPTER 5 ................................ ........... 132 LIST OF REFERENCES ................................ ................................ ............................. 135 BIOGRAPHICAL SKETCH ................................ ................................ .......................... 148

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8 LIST OF TABLES Table page 1 1 DMS aerosol phase products measured using a PILS IC at two different RH levels (10% and 45%) ................................ ................................ ......................... 38 2 2 Isoprene SOA experiments with and without DMS in the presence of NO x at RH=12%, 42% and 80% ................................ ................................ .................... 39 2 3 SOA formation from DMS photooxidation using an indoor chamber at RH=12% ................................ ................................ ................................ ............ 40 3 1 Isoprene SOA yield due to sodium sulfate aerosol, MSA aerosol or sulfuric acid aerosol ................................ ................................ ................................ ....... 58 3 2 Initial chamber conditio ns of the experiments used for product analysis a. .......... 59 3 3 Relative intensities of CI and EI mass spectra for PFBHA derivatives of isoprene photooxidation products ................................ ................................ ....... 60 4 1 Chamber experiments of the photooxidation of DMS and DMSO in the presence of NO x ................................ ................................ ................................ 80 4 2 Chamber experimental conditions for isoprene photooxidation with and wit hout DMS ................................ ................................ ................................ ....... 81 4 3 Model simulation of the yields of MSA and H 2 SO 4 and the integrating reaction rate s (IRR) of the formation of MSA and H 2 SO 4 ................................ ... 82 5 1 The concentrations of the organic and inorganic compounds in the ambient aerosol sampled in different sites ................................ ................................ ...... 99 5 2 P values of the concentrations of NO 3 MS and nss SO 4 2 for the prediction of the concentrations of 2 methyltetrol and secondary organic carbon (OC sec ) 100 5 3 The summary for the MS /ss SO 4 2 ratio, the contribution of SO 2 to SO 4 2 T the contribution of DMS to SO 4 2 T and wind direction for each sample ............ 101 A 1 DMSO photooxidation mechanisms ................................ ................................ 112 A 2 DMS photooxidation mechanisms ................................ ................................ .... 112 A 3 SO 2 photooxidation mechanisms ................................ ................................ ...... 121 A 4 Comparison of the wall loss rates of different chemicals in this study and those in literature ................................ ................................ .............................. 123

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9 A 5 Integrating reaction rate (IRR) of the initial reactions of DMS decay in different conditions ................................ ................................ .......................... 124 B 1 Relative intensities of EI mass spectra for BSTFA derivatives of 2 methyltetrols (P 1 ) and PFBHA derivatives of several carbonyls (P 2 P 5 ) ........... 132 B 2 The ranges of the initial concentrations of DMS and NO (ppb) and MS /DMS_SO 4 2 ratios the in different sites both in the morning and afternoon ...... 133

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10 LIST OF FIGURES Figure page 2 1 Anion chromatogram of the aerosol sample of D 1 s howing MSA, MSIA and sulfate. ................................ ................................ ................................ ................ 41 2 2 Major acid (MSIA, MSA and sulfuric acid) mass fraction of the total acidic aerosol mass in M 1, M 2 and D 1 (assuming MSIA, MSA and sulfuric acid are the only acidic aerosol products) ................................ ................................ .. 42 2 3 x iso and Y DMS values associated with M 1 (IC data) compared to those with M 5 (OC/EC data).. ................................ ................................ ............................. 43 2 4 I soprene SOA yields at different concentration of NO x or isoprene with and without DMS ................................ ................................ ................................ ...... 44 2 5 Isoprene SOA yields at different RH with and without DMS .. ............................. 45 2 6 Time profiles of aerosol growth and precursor decay for several experiments ( Exp. I 4 M 4 and D 5 ) ................................ ................................ ....................... 46 3 1 Chamber experiment procedures to study the impact of MSA on is oprene SOA growth (Figure 3 1A for Exp A1~A6). ................................ ......................... 61 3 2 The time profile of aerosol volume concentration (before wall loss correction) measured by SMPS for Exp H1 .. ................................ ................................ ........ 62 3 3 Reconstructed m/z = 181 ion chromatogram in the EI mode for PFBHA carbonyl derivatives originated from isoprene oxidation (both gas and particle phase products in the presence and in the absence of acids). ........................... 63 3 4 GC ITMS Mass fragmentation spectra (relative intensity vs. m/z) in the EI mode for PFBHA (P1~P11) derivatives of carbonyl products and BSTFA (P12) derivatives of 2 methyltetrol originated from isoprene photooxidation in the presence of NO x .. ................................ ................................ ......................... 64 3 5 Aerosol phase product yields (A) and gas phase product yields (B) determined using GC ITMS analyses for isoprene/NO x isoprene/DMS/NO x isoprene/NO x +MSA and isoprene/NO x +H 2 SO 4 ................................ ................ 65 4 1 The time profiles of DMSO, DMSO 2 SO 2 NO x and O 3 for the photooxidation of DMSO in the presence of NO x .. ................................ ................................ ...... 83 4 2 Model simulation of MSA and sulfuric acid for the photooxidation of DMSO in the presence of NO x with (SH) and without (SN) including heterogeneous reactions. ................................ ................................ ................................ ............ 84

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11 4 3 The time profiles of DMS, DMSO 2 SO 2 MSA, sulfuric acid, NO x and O 3 f or the photooxidation of DMSO in the presence of NO x ................................ .......... 85 4 4 The time profiles of isoprene, DMS, MSA and sulfuric acid for the photooxidation of DMS and NOx in the presence of 560 ppb (Exp iso DMS 1), 1360 ppb (Exp iso DMS 2), and 2248 ppb (Exp iso DMS 3) of isoprene.. ......... 86 4 5 The time profiles of Exp iso DMS 4 (isoprene, DMS, NO x and O 3 from the photooxidation of 31 ppb of DMS and 40 ppb of NO x in the presence of 210 ppb of isoprene) and time profiles for Exp iso DMS 5 (NO x O 3 MSA and H 2 SO 4 from 20 ppb of DMS and 15 ppb of NO x in the presence of 40 ppb of isoprene). ................................ ................................ ................................ ........... 87 5 1 Geographical location of the sampling sites and distribution of different types of wetland near sampling si tes. ................................ ................................ ........ 102 5 2 The predicted concentrations of 2 methyltetrol ( OC sec ) vs. the measured concentrations. ................................ ................................ ................................ 103 5 3 Concentration of differen t organic compounds in the ambient PM 2.5 collected at three different locations in different days. ................................ ..................... 104 5 4 Model predictions of MS /DMS_SO 4 2 at 10:30 EST (A) and 15:00 EST (B) using the sunlight spectrum of a typical sunny day with different initial concentrations of DMS and NO in the early morning assuming a constant flux of DMS during the day. ................................ ................................ ..................... 105 A 1 Mass fragmentation spectra in the EI mode (with GC retention time) for d6 DMSO, DMSO and DMSO 2 ................................ ................................ ............. 125 A 2 The time profiles of DMSO, DMSO 2 SO 2 NO x and O 3 for the photooxidation of DMSO in the presence of NO x .. ................................ ................................ .... 126 A 3 Model simulation of MSA and sulfuric acid for the photooxidation of DMSO in the presence of NO x with (SH) and without (SN) including heterogeneous reactio ns.. ................................ ................................ ................................ ......... 127 A 4 The time profiles of DMS, DMSO 2 SO 2 MSA, sulfuric acid, NO x and O 3 for the photooxidation of DMSO in the presence of NO x ................................ ....... 128 A 5 Mass fragmentation spectra in the EI mode (with GC retention time) for PFBHA derivatives of major carbonyl products originated from isoprene photooxidation in the presence of NO x ................................ ............................ 129 A 6 The time profiles of isoprene, P1 P4, NO x and O 3 from the photooxidation of isoprene in the presence of NO x (Exp iso 1 and iso 1 in Table 2). denotes the experimentally observed concentrations of chemical species and or those simulated using the kinetic model. ................................ ............... 130

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12 A 7 The time profiles of gaseous products (P1 P4), NO x and O 3 from the photooxidation of DMS and NO x in the presence of 560 ppb of isoprene (Exp is o DMS 1), 1360 ppb of isoprene (Exp iso DMS 2) and 2248 ppb of isoprene (Exp iso DMS 3). ................................ ................................ ............... 131 B 1 Linear regression of concentrations of the primary organic carbon versus concentrations of element ary carbon. ................................ ............................... 134

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13 LIST OF ABBREVIATION S GC ITMS G as C hromatography I on T rap mass spectrometer (GC ITMS) is an instrument for organic separation and analysis. PILS IC Particle Into Liquid Sampler coupled with ion chromatogra ph (PILS IC) is an on line instrument for the analysis of the soluble composition of aerosol. PM Particle matter (PM) is the term for a mixture of solid particles and liquid droplets found in the air. SMPS Scanning Mobility Particle Sizer Spectrometer (SMP S) is a high resolution nanoparticle sizer used to monitor the size distribution of polydispersed aerosols SOA Secondary organic aerosol (SOA) is a type of organic aerosol that is formed through the condensation of semivolatile organic compounds in the gas

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14 Abstract of Dissertation Presented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy STUDY OF THE AEROSOL FORMATION FROM THE MIXTURE OF ISOPRENE AN D DIMETHYL SULFIDE IN THE PRESENCE OF NO X By Tianyi Chen August 2012 Chair: Myoseon Jang Major: Environmental Engineering Sciences Past and current research findings suggest that the acid catalyzed heterogeneous reaction theory narrows the gap between t he ambient s econdary organic aerosol (SOA) data and the predicted SOA data using the precursor flux multiplied by the SOA yield determined from chamber experiments. In this study, a reduced sulfur compound that is predominantly from oceanic sources, dimeth yl sulfide (DMS) was proposed to be an additional source of aerosol acidity SOA created from the photooxidation of a mixture of isoprene and DMS was studied using a Teflon film indoor chamber and for different NO x concentrations (40 to 220 ppb) and relat ive humidit y values of 12%, 42% and 80%. Results obtained from c hamber experiments showe d that the isoprene S OA yield is increased by 30% to 1 50 % in the presence of DMS The impact of MSA on the SOA formation produced from photooxidation of isoprene in the presence of NO x w as investigated in a 2 m 3 Teflon film indoor chamber. Our study showed that MSA aerosol can significantly increase the isoprene SOA In order to model the SOA formation in the presence of MSA and H 2 SO 4 a prediction model of DMS photooxid ation was developed T he most recently reported reactions with their rate constants have been included. The model included in this study predicted that concentrations of both MSA and H 2 SO 4

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15 would significantly increase due to heterogeneous chemistry, and th is was well substantiated with experimental data. To confirm the DMS effect on SOA formation in the ambient air, the effect of MSA on increasing the SOA mass and the relative contribution of SO 2 and DMS to sulfate were evaluated through ambient aerosol sam ples. O ur results suggest that DMS is a significant source of acidic aerosol (H 2 SO 4 and MSA) in the coastal area and in the land surrounded by fresh water wetland or salt marsh.

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16 CHAPTER 1 INTRODUCTION Atmospheric A erosol and Secondary Organic Aerosol (SO A) Atmospheric aerosols (with a diameter larger than 3 nm), also known as liquid or solid particles suspended in air, have drawn great attention to researchers due to the climate effect (Kanakidou et al., 2005; Hans en and Sato, 2001) and health effect (Jang et al., 2006b; Baltensperger et al., 2008; Mokdad et al., 2004) One of the most difficult issue s to handle is the understanding of the aerosol composition. Generally speaking, atmospheric aerosol can be divided into two categories: primary aerosol and secondary aerosol. Primary particles are directly emitted from sources such as biomass burning, sea salt, dust and etc. Elemental carbon and most inorganic species in the aerosol are usually the components of primary particles. In contrast, secondary particles are formed through gas to particle conversion such as nucleation condensation and heterogeneous reactions. For example, NH 4 + is formed in the aerosol through t he ammonia t itration with acidic aerosols. Among all the secondary aerosol compositions, secondary organic aerosol (SOA) is of the greatest uncertainty in term of its chemical makeup and properties. It is estimated that 10 000 to 100 000 different organic compounds have been measured in the atmosphere (Goldstein and Galbally, 2009) SOA is also a major component of the total aerosol. In 37 field campaign, Zhang et al. (2007) found that of S OA is ubiquitous in various atmospheric environments, on average accounting for 64%, 83% and 95% of the total organic aerosol in urban, urban downwind and rural/remote sites, respectively.

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17 SOA Y ield and A cid C atalyzed H eterogeneous R eactions SOA Y ield Through atmospheric oxidation processes, many atmospheric gaseous pollutants or volatile organic compounds (VOCs, with vapor pressure larger than 10 2 Torr) such as isoprene, pinene, limonene c an form semi volatile compounds (with vapor pressure in the range of 10 6 to 10 2 Torr), which eventually condense to form aerosol. In air pollution, the amount of aerosol is simply quantified by mass regardless of the chemical composition and so is the S OA. In order to compare the ability of different precursors to produce SOA, precursor SOA yield ( Y ) is defined as follows (Odum et al., 1996) ( 1 1 ) where O M is the mass concentration of organic m atter (OM) formed and ROG is the mass concentration of the reactive organic precursor gas consumed. I soprene has relatively low SOA yields The isoprene SOA yield for photooxidation in th e presence of NO x were reported to be as low as 0.2% by Edney et al. (2005) and as high as 3% by Kroll et al. (2005, 2006) Considering the isoprene flux in the range between 250 and 750 TgC yr 1 (Lathiere et al., 2005) (it accounts for half of the total non methane VOC flux), the isoprene SOA flux should fall in the range of 0.5~22.5 TgCyr 1 As a matter of fact, based on the chamber experiment data coupled with biogenic volatile organic compound flux, b ottom up estimates give biogenic secon dary organic carbon (BSOC) fluxes of 9 ~ 50 TgCyr 1 In contrast, the top down estimate based on ambient data shows a much higher value: 140 910 TgCyr 1 (Goldstein and Galbally, 2007)

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18 The difference between the top down estimate and bottom up estimate indicates that there are possibly either unknown SOA precursors or a dditional reaction mechanisms. Acid Catalyzed Heterogeneous Reactions The acid catalyzed hetero geneous reaction theory proposed by Jang et al. (2002) cast some light to nar rowing the gap between the measured ambient SOA mass and predicted ambient SOA mass derived from the precursor flux and the SOA yield determined from chamber experiments. It was suggest ed that acidic sulfates significantly impact SOA formation via aerosol phase heterogeneous chemistry and formation of nonvolatile organics, called humic like substance (HULIS). L ater, Limbeck et al. (2003) also reported that colored polymeric products were formed through heterogeneous reactions from dienes in the presence of sul furic acid. One apparent influence of the acidic sulfates on the isoprene photochemical irradiation is the increase in SOA yields. For example, Edney et al. (2005) reported nearly a 1000% increase of isoprene SOA yield in the presence of SO 2 compared to SOA yield without SO 2 Czoschke et al. (2003) reported that the SOA yield produced from ozonolysis of isoprene increases by almost 200% because of preexisting sulfuric acid aerosol. Another markedly finding in isoprene SOA is the catalytic formation of 2 methyltetrols in t he presence of acid in ambient as isoprene marker compound s (Claeys et al., 2004) Later Paulot et al. (2009) have reported the existence of epoxide in the gas phase of the p hoto oxidation process of isoprene and have regarded epoxide as a link between gas and aerosol phase products from the atmospheric oxidation of isoprene. In recent NMR studies, Minerath et al. (2008; 2009) have co nfirmed the possibility of the formation of organosulfates and 2 methyltetrols from isoprene derived

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19 epoxides such as i soprene e poxydiols (IEPOX). 1 ,4 dihydroxy 2,3 epox ybutane (BEPOX), a structurally related surrogate of IEPOX, was found to be rapidly ab sorbed by acidified sulfate seed aerosols in chamber study (Surratt et al., 2010) M ore recently, IEPOX was synthesized and experimentally proved to be the precursor of several structures found in isoprene SOA, in cluding 2 methyltetrols and the conversion from IEPOX to isoprene SOA was strongly dependent on the aerosol acidity (Lin et al., 2011) Dimethyl S ulfide, A M issing A cidic S ource Although quite a few studies have been con ducted on the SOA of different precursors in the presence of sulfuric acid or ammonia bisulfate (Surratt et al., 2007b; Surratt et al., 2007a; Northcross and Jang, 2007; Kleindienst et al., 2007; Jang et al., 2006a; Iinuma et al., 2004; Gao et al., 2004; Czoschke et al., 2003) up to date, the current SOA model still much underestimates the ambient SOA mass. Acid source is more than anthropogenic ones. In nature, there is one group of compounds that can also produ ce s ulfuric acid: reduced sulfur. Of all the reduced sulfur (with a flux of 24 Tg y 1 ) (Pham et al., 1995 ) dimethyl s ulfide (DMS) flux accounts for 90%. DMS is originated mainly from ocean and is important for the understanding of climate change (Bates et al., 1987;Charlson et al., 1987) and atmospheric chemical proc esses (Andreae et al., 1995; Aranami et al., 2002) DMS released to the atmosphere is converted to sulfuric acid and m ethanesulfonic acid (MSA), both of which contribute to the formation of cloud condensation nuclei (CCN) and the change of the global radiation budget thus altering the climate (Charlson et al., 1987) Recently, Froyd et al. (2010) discovered that marine dimethyl sulfide emissions help generate secondary biogenic aerosol mass from isoprene oxidation products t hroughout the troposphere However, Froy d et al. attributed the heterogeneous

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20 reaction only to the formation of sulfuric acid from DMS and failed to explore the function of MSA as a major product of DMS. Similar to sulfuric acid, MSA ( pK a = 2) is a strong acid and ubiquitous in the ambient. For example, the gaseous MSA concentration in the eastern Mediterranean was reported to be in the range of 0.002~0.02 pptv and the particulate MSA concentration was 19.6 ~ 75.5 ng m 3 (Mihalopoulos et al., 2007) The data from the Palmer Station on Anvers Island in the Antarctic during February showed an average of 0.039 pptv of MSA in gas form and 181. 5 ng m 3 MSA in aerosol form (Jeffers on et al., 1998) From ambient samples in Riverside, CA, Gaston et al. (2010) found that up to 67% of the sub micrometer aerosol contained MSA Lukas et al. has detected 31.5 ng m 3 MSA in the ambient air in Kp uszta, Hungry (Lukacs et al., 2009) It is highly probable that by producing sulfuric acid and MSA, DMS can increase SOA mass through enhanced heterogeneous reactions of semivolatile organics. In seaside area, the effect of the enhanced heterogeneous reactions can be potentially high since DMS is marine borne. DMS C hemistry The major aerosol phase products of DMS are methanesulfonic acid (MSA) and sulfuric acid (Bardouki et al., 2003; Barone et al., 1995; Gaston et al., 2010; Lukacs et al., 2009) both of which are postulated to have significant effects on the earth radiation budget (Charlson et al., 1987) The Intergovernmental Panel on Climate Change (IPCC) has classified the aerosol originated from DMS as one of the important components to be well understood in the planetary climate system (IPCC, 1995) DMS photooxidation mechanism is an important part to understand the role DMS plays in the earth sulfur cycle and climate system. Since 1990, many detailed reviews of the comprehensive DMS oxidati on chemistry have been given (Yin et al., 1990b;

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21 Turnipseed, 1993; Urbanski and Wine, 1999; Barnes et al., 2006) However, large deviation of DMS products still exists between the ambient measurement and the simul ation results, e.g., dimethyl sulfoxide (DMSO) (Chen et al., 2000) H 2 SO 4 and MSA (Lucas and Prinn, 2002b) The deviation was generally attributed to the uncertainty of th e gas phase reaction rate constants and the lack of MSA and sulfuric acid formation mechanisms through heterogeneous reactions of DMS oxidation products (e.g., DMSO) on the surface of aerosol. To reduce these uncertainties, a modified DMS explicit model t hat can simultaneously predict the DMS aerosol formation is needed. Using a new DMS photoxidation model coupled with the isoprene photooxidation model extracted from Master s Chemical Mechanism (MCM) v3.2 ( http://mcm.leeds.ac.uk/MCM/ ), it is possible to un derstand the reasons for the lower MSA production in the presence of higher isoprene. In this study, a modified explicit model for DMS photooxdiation was given. To test the model, DMS photooxidation in the presence of NO x was studied using a 2 m 3 indoor c hamber. The DMS decay, ozone formation and the major DMS products, DMSO, dimethyl sulfoxide (DMSO 2 ), MSA and sulfuric acid were measured and compared with the simulation results. To study the influence of atmospheric VOCs on the DMS aerosol formation, t he MSA and sulfuric acid formed from DMS photooxidation in the presence of isoprene were simulated and compared with the measurement. Isoprene was chosen as a VOC representative due to its abundance in nature with its flux similar to that of methane (Guenther et al., 2006) D MS E ffect on SOA in A mbient A ir SO 2 has been known as the major source of sulfuric acid for long (Takahashi et al., 1975) Due to the large anthropogenic emission, SO 2 flux is roughly 83% of the total

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22 sulfur flux on earth (Pham et al., 1995) As a comparison, the largest marine borne sulfur compound, dimethyl sulfide (DMS) only accounts for 15. 5% of the total sulfur flux. Hence, it seems reasonable to use sulfuric acid to represent the total sulfur compounds in the air in the study of acid effect on SOA. However, since both SO 2 and DMS are extremely unevenly distributed on earth and 1.6% of DM S flux is from terrestrial vegetation and microorganism (Pham et al., 1995) in certain areas, the acidic products [e.g., sulfuric acid and methanesulfonic acid (MSA)] through DMS photochemical reactions may be more important than the acids converted from SO 2 That is to say, the sulfate formation from DMS photooxidation should not be neglected in some regions. This is supported by Berresheim et al. (1993) who estimated 15% 50% of contribution of reduced sulfur to the total non seasalt sulfate in the coastal and wetland areas in Georgia and Louisiana DMS has been known to be produced from two sources: 1) the algal derived compound dimethylsulfoniopropionate in surface ocean waters and salt marshes (Dacey et al., 1987) and 2) thiols in anaerobic sediments (Finster et al., 1990) and in a variety of oxic freshwater wetland s (Drotar et al., 1987) Therefore, air from representative areas containing DMS from both of the two sources needs to be investigated.

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23 CHAPTER 2 SECONDARY ORGANIC AEROSOL FORMATION FROM PHOTOOXIDATION OF A MIXTURE OF DIMETHYL SULFIDE AND ISOPRENE Background Dimethyl sulfide (DMS) is an important marine borne reduced sulfur compound with an estimated flux of 1 5.4~28.0 Tg S y r 1 (Aumont et al., 2002; Bopp et al., 2003 ; Kloster et al., 2006) A large amount of ambient monitoring data suggests that DMS photooxidation produces fine particles which consist primarily of sulfuric acid and methanesulfonic acid (MSA) (Gaston et al., 2 010; Lukacs et al., 2009; Bardouki et al., 2003; Barone et al., 1995) These fine particles have the potential effect on the over the oceans, leading to increases in plane tary albedo (Charlson et al., 1987) Thus, studies of DMS oxidation have been investigated by many researchers to understand DMS products and their impact on cloud chemistry. Despite many studies th r ough controlled chamber experiments and field observations, many details about DMS photooxidation mechanisms, the aerosol formation, and the kinetic model remain controversial. For example, most chamber studies of DMS oxidation products have been operated solel y for the reactions of DMS with OH radicals under both NO x free and NO x containing conditions (Arsene et al., 1999; Barnes et al., 1996 ; Librando et al., 2004; Yin et al., 1990a; Yin et al., 1990b) but no impact of coexisting volatile organic compounds ( VOCs ) has been considered. The atmospheric VOCs coexisting with DMS can modify gas phase chemistry of DMS, such as RO 2 radical chemist ry, the production of OH radicals,

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24 and the ozone formation associated with the production of O( 1 D). These modified gas phase reactions due to VOCs can also influence chemical distributions of DMS oxidation products that are directly related to DMS aerosol formation. In addition to the complexity of DMS oxidation due to the coexisting VOCs, the aerosol phase heterogeneous reactions of DMS products with atmospheric organic compounds have not been elucidated yet. For example, Jang et al. (2002) have proposed that atmospheric organics, which are partitioned to aerosols, can be further transformed via heterogeneous reactions, particularly in the presence of submicron sulfuric acid aerosols. The direct outcome of heterogeneous acid catalyzed reactions is the formation of o ligomeric matter in aerosol and an increase in SOA mass. Besides sulfuric acid, DMS produces MSA which, being a strong acid ( pKa = 2) may also enhance the heterogeneous reactions of atmospheric organic compounds increasing SOA production Up to date, the simulation of DMS photooxidation against field data has been co nducted using an explicit gas phase mechanism coupled with a few simple aerosol phase reactions (Karl et al., 2007; Lucas and Prinn, 2002b, 2005) or the semiempirical gas and particle kinetic models based on the fi tting parameters to field data (Chen et al., 2000; Davis et al., 1999; Mari et al., 1999) However, these simplified DMS oxidation mechanisms are not satisfactory in prediction of DMS oxidation products such as di methyl sulfoxide (DMSO) (Chen et al., 2000) H 2 SO 4 and MSA (Lucas and Prinn, 2002b) Th is deviation is caused by the uncertainty of the gas phase reaction rate constants f or both DMS and DMS products and the lack

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25 of MSA formation mechanisms through heterogeneous reactions of DMS oxidation products on the surface of aerosol In addition, none of previous models included the aerosol phase heterogeneous reactions of DMS produ cts with atmospheric semivolatile oxygenated compounds, which are mainly originated from secondary organic aerosol (SOA) due to the photooxidation of VOCs. In this study, in an attempt to understand the interaction between the oxidations of DMS and SOA pre cursors, the photooxidation of a mixture of isoprene and DMS was explored using an indoor Teflon film chamber under various NO x concentrations and relative humidities (RH). Isoprene was chosen as a representative of biogenic SOA precursor s not only becaus e it has a large emission (440 660 TgC yr 1 about same as the global methane flux) (Guenther et al., 2006) but also because its SOA yields are high ly sensiti ve to aerosol acidity For example, Czoschke et al. (2003) reported that th e SOA yield produced from the ozonolysis of isoprene increases by almost 200% when there is preexisting sulfuric acid aerosol. Edney et al. (2005) showed a 1000% increase in the isoprene SOA yield in the presence of SO 2 T o investigate the impact of isoprene on the DMS aerosol, t he DMS aerosol products (with and without isoprene) were quantified using a Particle Into Liquid Sampler coupled with Ion Chromatograph (PILS IC). To evaluate the DMS impact on the isoprene SOA formation, the isoprene SOA yield s in the DMS/isoprene/NO x system w ere also calculated u si ng a new approach implementing an O rganic C arbon ( OC ) analyzer, and compared with those in the absence of DMS

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26 Experimental Section Teflon Film Indoor Chamber Experiments All SOA experiments were conducted in a 2 m 3 indoor Teflon f ilm chamber equipped with UV Visible lamps (Solarc Systems Inc., FS40T12/UVB) covering all wavelengths ranging between 280 900 nm. Prior to each experiment, the chamber was flushed using air from clean air generators (Aadco Model 737, Rockville, MD; Whatm an Model 75 52, Haverhill, MA). Precursor organics were added to the chamber by passing clean air through a T union where the chemicals were injected using a syringe while NO x gas was introduced using a syringe through a certificate NO tank (99.5% nitric oxide, Linde Gas). SOA experimental conditions and resulting SOA data at different relative humidity (RH=12%, 42% and 80%) are summarized in Tables 2 1 2 2 and 2 3 Chemicals and I nstruments. All the organic chemicals ( purity levels 98% ) were purchased from Aldrich (Milwaukee, WI). The ozone concentration was measured by a photometric ozone analyzer (Teledyne model 400E) while the NO x concentration was measured using a chemiluminescence NO/NO x analyzer (Teledyne Model 200E) A fl uorescence analyzer ( Teledyne Model 1 0 2 E) was used to measure SO 2 and Total Reduced Sulfur (TRS, gas phase) concentration The particle size distribution was monitored with a Scanning Mobility Particle Sizer (SMPS, TSI, Model 3080, MN) combined with a con densation nuclei counter (CNC, TSI, Model 3025A). The SMPS data was corrected for the aerosol loss due to the chamber wall with a first order decay

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27 (Mcmurry and Grosjean, 1985) The gas phase concentration of the precursor s w as measured using an HP 5890 Gas Chromatogra phy Flame Ion ization Detector (GC FID). A PILS IC (Metrohm, 761 Compact) was used to measure the major aerosol products produced from DMS photooxidation The PILS IC sample was collected at the end of each chamber experiment ( Exp M 1, M 2 and D 1 ). The d etection limit of PILS IC is 2 g m 3 and the associated error is 6% The aerosol sampling flow rate was 13 L min 1 and the liquid flow rate in the anion column was 0.7 mL min 1 A basic denuder, coated with 1% glycerol and 2% K 2 CO 3 in ethanol water (1:1), was placed upstream of the PILS to remove gaseous acids. For measuring OC data the aerosol was analyzed at the end of each experiment with a semi continuous OC/EC carbon aerosol analyzer (Sunset Laboratory Model 4) using the NIOSH 5040 method The detection limit of OC analysis is 0.3 g m 3 (for 120 minutes sampling) a nd the associated error is 10% The sampling flow rate for OC analyse s was 8 L min 1 The sampling time varied between 40 and 120 minutes, depending on the mass concentration of aerosols in the chamber. Results and D iscussion PILS IC D ata to S tudy the I mpact of I soprene on DMS A erosol F ormation T he products of DMS / NO x photooxidation with isoprene were characterized using a PILS IC and compared to those without isoprene Figure 2 1 show s a typical ion chromatogram for DMS photooxidation products, which mainly include s methanesulf i nic acid (MSIA), MSA and sulfuric acid. F or the analysis of MSIA and MSA no interference due to gaseous carboxylic acids (e.g., formic acid and acetic

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28 acid) appears when a denuder coated wit h a mixture of 1% glycerol and 2% K 2 CO 3 in ethanol water upstream the PILS removes these carboxylic acids which are produced from photooxidation of isoprene Table 2 1 summarizes aerosol phase DMS product distribution in both the presence (M 1 and M 2) a nd the absence (D 1) of isoprene. MSA accounts for the highest aerosol mass fraction (70% on average, see Figure 2 2) among the three major DMS aerosol products. Unlike the DMS/NO x system mainly comprising MSA, MSIA and sulfuric acid the aerosol produced from the DMS/isoprene/NO x system may also contain irreversible organosulfates ( nonelectrolyte s) that are formed through the reaction of isoprene products and the acids originated from DMS photooxidation. T he PILS IC method may underestimate the sulfur co mpounds in the DMS aerosol in the presence of isoprene. However, the DMS yields using the PILS IC data agree well with those obtained from the OC Comparison of PILS IC and OC ). Such a tendency sugges ts that the organosulfates pro duced if any, are reversible during the PILS IC analysis where hot water steam is used for the aerosol extraction. The t otal sulfur molar yields in M 1 and M 2 were calculated (Table 2 1) without the wall loss correction for the total reduced sulfur (TRS ). The total identified sulfur molar yield without isoprene (D 1) reach es almost 8 9 % and that with isoprene (M 1 and M 2), on average 78% (Table 2 1) T he wall loss of polar products (e.g MSA and MSIA) and the heterogeneous reaction of DMS products wit h isoprene products

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29 on the chamber wall would contribute to the unidentified sulfur molar yield s (11% for D 1 and 22% for M 1 and M 2) OC A nalysis to S tudy the I mpact of DMS on I soprene SOA Y ields The typical SOA yield for a single precursor is described as (Odum et al., 1996) ( 2 1 ) w here is the mass concentration ( g/m 3 ) of organic matter formed and is the mass concentration ( g/m 3 ) of the consumed reactive organic gas T o estimat e the SOA yield for each precursor in the mixture of DMS and isoprene the total aerosol mass, is separated into the OM associated with DMS ( ) and the OM associated with isoprene ( ). We define t he mass fraction of isoprene SOA in as x iso and the mass fraction of DMS aerosol in as x DMS ( 2 2 ) ( 2 3 ) Both x iso and x DMS range between 0 and 1 Then, the isoprene SOA yield ( Y iso ) in the presence of DMS c an be expressed as: ( 2 4 ) where is the consumed isoprene mass concentration In this study an OC analysis was used to estimate x iso and x DMS The organic carbon ( OC DMS iso ) in the aerosol produced from photooxidation of the

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30 isoprene / DMS /NO x system is the sum of OC contributed by isoprene ( ) and DMS ( ). ( 2 5 ) E ach side in E q. 2 5 is divided by ( 2 6 ) By a dding E q. 2 2 and 2 3 into E q. 2 6, the equation can be transformed into ( 2 7 ) We assume that / for the DMS/isoprene/ NO x system is not significantly different from / for the isoprene/ NO x system, where OC iso is the organic carbo n mass formed from the isoprene/NO x system (no DMS) at a given experimental condition and OM iso is the total aerosol mass in the same system. Similarly, we assume / / where OC DMS and OM DMS are for the aerosol from the DMS/NO x system (no isop r ene) respectively. Table 2 1 shows OC DMS /OM DMS values for M 1, M 2 and D 1 which are estimated using the chemical composition of DMS aerosol product s (MSA, MSIA and sulfuric a cid ) ( Figure 2 2 ) and the carbon fractions of each acid (0.125 for MSA, 0 for sulfuric acid and 0.15 for MSIA). The resulting OC DMS / OM DMS values of the aerosol from the DMS/NO x system were 0.10 and close to / ( 0 .11 ) of the DMS/isoprene/NO x aerosol, supporting the assumption / / ( within the 8.5 % statistical error see superscript h. in Table 2 1 ). Then, E q. 2 7 can be rewri tten as

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31 ( 2 8 ) The organic mass ( OM iso ) in the isoprene/NO x system can be estimated from the isoprene SOA density ( iso ) and isoprene SOA volume ( V iso ) using SMPS data. ( 2 9 ) The organic mass ( OM DMS ) in the DMS/NO x system and the organic mass ( OM DMS iso ) in the isoprene/ DMS/NO x system can be desc ribed in a similar way, ( 2 10 ) ( 2 11 ) where V DMS is the DMS aerosol volume and DMS is the DMS aer osol density V DMS iso and DMS iso correspond to the volume and the density of the aerosol of the isoprene and DMS mixture system, respectively. DMS iso is estimated approximately by the following equation. ( 2 12 ) Using E q. 2 9 ~ 2 12, E q. 2 8 can be rewritten as ( 2 13 ) E quation 2 1 3 is rearranged to solve for x iso ( 2 14 )

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32 where iso (1.1 g/cm 3 ) and DMS ( 1. 2 g/cm 3 ) are experimentally determined us ing SMPS data and the aerosol mass collected on the filter. OC iso OC DMS and OC DMS iso are determined by the OC/EC analyzer V iso V DMS and V DMS iso are analyzed by the SMPS. T he OC iso /V iso values of the isoprene/NO x system range from 0.56 to 0.59 at RH = 12% and those of the isoprene/DMS/NO x system, 0.31 0. 42 (Table 2 2 ). The OC DMS /V DMS value in this study is fixed at 0.1 3 for NO x reactions ( OC DMS /V DMS in Table 2 3 ). The resulting x iso values are listed in Table 2 2 The Y iso values reported in Tab le 2 2 are estimated using eq. 2 with OM iso OM iso DMS x iso and ROG iso W hen we take into consideration the esterification of DMS major products (MSA and sulfuric acid) with isoprene products, / can be slightl y larger than / because d ecreases with water evaporation a concurrent process associated with esterification. Considering esterification is th erefore needed to correct the / calculation When we assume that all the produced MSA and sulfuric acid are converted to esters ( maximum esterification), t he mass loss fraction of MSA due to esterification is 18/96 where 18 and 96 are the molecular weight o f water and MSA respectively ; the loss fraction of sulfuric acid is 36/98 where 36 is the molecular weight of 2 moles of water and 98 is that of 1 mole of sulfuric acid. Using the chemical composition information ( Figure 2 2 ) the estimated mass loss fra ction of due to esterification is 0.20 suggesting that / = 1.25 / ( no reaction ). x iso ( maximum esterification ) is only 7.2% smaller than x iso (no reaction), which is within the 11.4%

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33 error range (see x iso in Table 2 2). Thus, we will only report the data without water loss correction in the following discussion. Comparison of PILS IC and OC D ata T he OC/EC data are compare d to the PILS IC data t o evaluate the validity of the two methods For example, the PILS IC measurement in M 1 (Table 2 1) and the OC/EC analysis in M 5 (Table 2 2) were conducted in similar experimental conditions Figure 2 3 summarizes x is o and Y DMS from M 1 and M 5 Both m ethods show similar results in either x is o or Y DMS : e.g. x is o = 32.0% based on IC data and x is o = 37.8% from OC data; Y DMS = 39.6% based on IC data and Y DMS = 35.5% from OC data. Consistency between the two methods is also observed for the OC DMS / OM DMS d ata: 0.11 for D 1 using IC (Table 2 1) and 0.12 for D 4 using OC/EC (Table 2 3). Thus, we conclude that the OC/EC approach is an appropriate method to estimate the decoupled aerosol yield s ( Y iso and Y DMS ) in the binary mixture and that the PILS IC analysi s reasonably quantifies the major DMS aerosol phase products in the presence of isoprene The I mpact of DMS on the I soprene SOA Y ield : NO x E ffects T he impact of DMS on Y iso was analyzed by comparing Y iso with DMS to that without DMS at given NO x and isopre ne concentration s. Figure 2 4 A presents Y iso at a given isoprene concentration (850 ppb) and humidity (RH=12%) with varying NO x concentrations (40 ~ 220 ppb) with and without DMS. Figure 2 4 B shows Y iso at a given NO x concentration (40 ppb) and humidity (RH=12%) with varying isoprene concentrations (100~850 ppb) with and without DMS. T he percentage increase of

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34 Y iso due to DMS ( % Y iso ) is summarized in Table 2 2 T he resulting % Y iso values ( between 32 6 % and 9 8 9 % ) suggest that Y iso is significantly el evated by DMS in a wide range of NO x concentration s. The I mpact of DMS on I soprene SOA F ormation : RH E ffects I n Figure 2 5, t he Y iso both with DMS and without DMS at RH=12% were compared with th ose at higher RH s ( 42% and 80%), with two initial NO x concentr ations (40 ppb and 8 0 ppb) at a given isoprene concentration (850 ppb). Overall, % Y iso (Figure 2 5) wa s much higher at high RH compared to that at low RH. Humidity can influence b oth gas phase chemistry and aerosol phase reactions inside the chamber. In the presence of NO x higher OH radical s can be formed though the reaction of O( 1 D) with a water molecule. Under our experimental condition, isoprene is present over the entire chamber experiment. Thus, the additional OH radicals due to higher humidity are more likely consumed by isoprene instead of producing highly oxidized products. On the other hand, the higher humidity can reduce HO 2 radicals in the gas phase (Kanno et al., 2005) influencing the formation of ROOH. It is known that ROOH can further react with an aldehyde and produce high m olecular weight hemiacetal in the aerosol (Johnson et al., 2004) Hence, isoprene SOA yields decrease with increasing hum idity. The greater % Y iso at the high RH condition (Figure 2 5) is mainly due to the higher amount of acid formed from DMS photooxidation The formation of MSA on the aerosol surface is enhanced by higher RH due to the aqueous processing from MSIA The higher MSA accelerates aerosol phase heterogeneous reaction s of

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35 organic compounds increasing SOA formation Th is explanation is supported by the MSA mass yield and DMS aerosol mass fraction ( x DMS ) of the total aerosol mass listed in Table 2 1 For exampl e, the MSA mass yield is 25.8% at RH=10% ( M 1 in Table 2 1) compared with 33.4% at RH=45% ( M 2 in Table 2 1). In addition, the DMS aerosol fraction in the total aerosol ( x DMS ) is 68.0% ( M 1 ) at RH=10% and 56.0% (M 2) at RH=45%, indicating stronger heterogen eous reactions at higher RH that drive more volatile isoprene products onto the aerosol. The I mpact of DMS on I soprene SOA F ormation : A erosol G rowth P attern T he impact of DMS on Y iso was also investigated for the aerosol growth pattern between the isoprene only system and the mixture system. The time profiles of the SOA mass and isoprene concentrations with DMS ( M 4 ) and without DMS ( I 4 ) are shown in Figures 2 6A The time profile for DMS aerosol mass and DMS concentration (D 5) is shown in Figure 2 6B In Figure 2 6 A t he photoirradiation of the isoprene only system shows a 40 minute induction period (no significant SOA growth) the time to reach the saturation of the gas phase isoprene oxidation products. In contrast, rapid aerosol growth occurre d fro m the beginning of SOA experiment in the DMS photoirradiation system owing to the self nucleation of H 2 SO 4 The dynamics of aerosol growth patterns shown in Figure 2 6 indicate that the DMS aerosol forms before the condensation of isoprene oxidation produ cts when the mixture of isoprene and DMS are photoirradiated together. The pre form ed acidic products from DMS photooxidation can serve not only as catalysts that facilitate the formation of methyl tetrols and nonvolatile oligomers from reactive organic

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36 c ompounds (e.g., glyoxal and methyl glyoxal) but also as reactants that produce organosulfates (Iinuma et al., 2007; Liggio and Li, 2008; Minerath et al., 2008; Minerath et al., 2009; Paulot et al., 2009) Uncertainties The uncertainties associated with the use of the indoor chamber include the temperature increase ( ~6K ) due to UV p hotoirradiation lamps The temperature change can affect the gas particle partitioning of semivolatile products onto aerosols (Carlton et al., 2009) The artificial light sources producing wavelengths in the range of 280 and 900 nm different from the actual natural sunlight can lead to different product compositions (Warren et al., 2008) In addition, t he progression of heterogeneous chemistry on the chamber wall between organic and inorganic species could potentially reduc e the effects of heterogeneous reactions on the surface of the SOA To minimize the uncertaint ies a large outdoor chamber facility currently under construction at the University of Florida wil l be used for future studies. In addition, the detailed clarification of the mechanism s of the impact of DMS on isoprene SOA formation is needed based on the analytical stud ies of both the gas and aerosol phase product s Atmospheric I mplications Our st udy is beneficial for evaluating the potential impact of DMS as a reduced sulfur compound on SOA formation in the ambient air especially near seaside areas We have observed significant Y iso increase s due to DMS at an atmospheric relevant RH (42%) conditi ons using the given mixing ratio (Table 2 2). T he isoprene

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37 concentration in the coastal area is 200~800 pp t varying with season and location (Bottenheim and Shepherd, 1995; Holzinger et al., 2002; Yokouchi, 1994) and the coastal concentration of DMS is usually 50~200 ppt (Ramanathan et al., 2001) Thus, possible mixing ratios of isoprene to DMS can range from 1 to 16 in coastal areas T herefore the m ixing ratio of 7.5 used in our study falls into the actual ambient mixing ratio range Based on the tendency in Y iso as a function of NO x (Figure 2 4A), Y iso value of this study was not strongly dependent of NO x concentrations but was significantly affected by the presence of DMS. A lthough concentrations of isoprene DMS and NO x are higher in our study than those in ambient the similar impact of DMS on Y iso would occur in the ambient air. For example, Froyd et al. (2010) have recently discovered a significant loss of gaseous epoxide (characteristic product of isoprene photooxidation in ambient) to the acidi c aerosol during the maritime convective lofting of DMS Their observation suggests that heterogeneous reactions of isoprene SOA products on the surface of the acidic aerosol, which is produced from DMS oxidation, can increase isoprene SOA yields in the ambient air Further field studies are required in the future to find more evidence for the effect of DMS on isoprene SOA formation in the ambient atmosphere.

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38 Table 1 1 DMS aerosol phase products measured using a PILS IC at two different RH levels (1 0 % and 4 5 %) E xp. a NO x b ppb Isoprene b ppb DMS b ppb ( g/m 3 ) DMS ppb ( g/m 3 ) OM g/m 3 Yield100% c Y DMS 100% mass d Total S yield 100% molar f x DMS 100% (IC) g OC DMS / OM DMS (IC) h MSIA d MSA d H 2 SO 4 d SO 2 molar TRS molar e mass mass mass (molar) (molar) (mol ar) RH=10% M 1 185 800 140 70 103.8 4.4 25.8 9.4 29.7 19.2 39.6 76.3 68 0.10 ( 354 ) ( 177 ) (3.4) (16.7) (7.3) D 1 200 0 170 71 108.3 4.8 48 8.4 37.3 12.3 61.1 88.9 100 0.1 1 ( 431 ) ( 177 ) (3.7) (31) (4.6) RH=45% M 2 181 847 139 56 126.7 6.8 33.4 9.8 32.8 14.0 50.0 79.8 56 0.1 0 ( 352 ) ( 142 ) (5.3) (21.6) (6.2) a. M: the mixture of isoprene and DMS experiment ; D : the photooxidation of DMS only b. Initial concentration c. All the aerosol yield data were corrected f or the wall loss using the first order decay r ate The estimated uncertainty (1 0 %) is calculated from errors associated with SMPS (2%), PILS IC (6%), SOA density (5%) and ROG iso (6%). d. A erosol phase products only. e. TRS: T otal reduced sulfur i ncluding all the gas phase sulfur other than DMS. The TRS yield was not corrected for the wall loss. f. Total s ulfur yield = MSIA aerosol yield+ MSA aerosol yield+ H 2 SO 4 aerosol yield+ SO 2 yield+ TRS yield. MSIA, MSA and H 2 SO 4 aerosol yield have been corr ected for wall loss. g x DMS is defined by eq. 3. x DMS (IC) is determined using an PILS IC a ssum ing that MSA, MSIA and H 2 SO 4 are the only aerosol phase products of DMS. x DMS (IC) =(MSIA mass+ MSA mass+ H 2 SO 4 mass )/total aerosol mass ( OM ). The assumption here is valid because the calculated x DMS of D 1 (no isoprene) reaches the theoretical value, 100%. h OC DMS / OM DMS (IC) = (0.1 5 MSIA mass+0.125 MSA mass)/(MSA mass+ MSIA mass+ H 2 SO 4 mass) The MSIA and MSA carbon fraction s of the total molecular weig ht are 0.15 and 0.125, respectively The estimated uncertainty is 8.5 % based on the uncertainty of PILS IC (6%)

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39 T able 2 2 Isoprene SOA experiments with and without DMS in the presence of NO x at RH=12%, 42% and 80% a Exp. b NO x ppb DMS ppb Isopr ene ppb g/m 3 g/m 3 g/m 3 OC/V c x iso 100% d,h Y iso 100% e,h Y DMS 100% f,h iso g,h RH=(122)% M 3 48 119 850 241 26.6 6.8 0.38 56.7 (53.2) 1.6 (1.5 ) 11.1 5 1 % (4 2 %) (11.90) I 3 40 0 870 47 9 0 5.1 0.56 100 1. 1 n.a. M 4 86 103 872 784 33.9 19 0.37 54.3 (50.7) 1.3 (1.2 ) 25.6 3 5 % (2 7 %) (27.50) I 4 87 0 860 651 0 6.3 0.56 100 1.0 n.a. M 5 220 129 880 2355 203.5 116.3 0.31 37.8 (33.2) 1. 9 (1.6 ) 35.5 9 9 % (7 5 %) (37.90) I 5 21 0 0 920 2437 0 22.9 0.59 100 0.9 n.a. M 6 42 30 210 475 27.3 10.5 0.40 57.4 (54.2) 1. 3 (1.20) 16.4 3 3 % (26%) (17.50) I 6 55 0 210 541 0 5.2 0.59 100 1.0 n.a. M 7 44 15 100 257 n.a. 6.3 0.42 61.3 (58.5) 1.5 (1.4 ) n.a. 6 9 % (6 1 %) I 7 57 0 100 257 0 2.3 0.59 100 0. 9 n.a. RH=(422)% M 8 40 100 820 446 n.a. 9.2 0.36 55.9 (52.1) 1. 2 (1. 1 ) n.a. 7 9 % (65 %) I 8 40 0 810 445 0 2.9 0.53 100 0. 7 n.a. M 9 81 100 840 681 n.a. 18.6 0.31 46.1 (41.2) 1. 3 (1.1 ) n.a. 12 5 % (97 %) I 9 95 0 88 0 1051 0 5.96 0.50 100 0. 6 n.a. RH=(802)% M 10 30 120 851 865 n.a. 23.4 0.31 41.8 (37.0) 1.1 (1.0 ) n.a. 98% (75 %) I 10 40 0 1030 1635 0 9.4 0.54 100 0. 6 n.a. M 11 85 130 1050 1335 n.a. 30.6 0.33 47.2 (42.7) 1. 1 ( 1.0 ) n.a. 1 50 % (124 %) I 11 81 0 1040 1380 0 6.3 0.54 100 0. 5 n.a. a. Temperature was 21~24 C and the aerosol concentration s in the background air were 0. 1 ~0.2 g/m 3 Refer to the su per scripts in Table 2 1 b. I : isoprene experiment (no DMS). c. The ratio of the OC mass concentr ation to total volume concentration of aerosols. OC/V value s ( g cm 3 ) were determined using an OC/EC analyzer and SMP S d x iso is defined by eq. 2 Its uncertainty ( 11.4 % ) was estimated from errors associated with SMPS, OC/EC ( 10 %) and SOA density e The maximal isoprene SOA yield with and without DMS (see eq 4 ). The uncertainty was estimated from errors associated with SMPS, OC/EC, SOA density and ROG. The uncertainty for the single precursor SOA yield was 8% and that for SOA yields in the mixtu re was 13.8%. f The maximum DMS aerosol yield ( Y DMS ) in the presence of isoprene. Y DMS = OM (1 x iso )/ DMS The uncertainty associated with Y DMS is 13.8%. g Percentage of Y iso increase due to DMS % Y iso = ( iso Y iso )/ Y iso where iso is the isop rene SOA yield in the presence of DMS and Y iso is the yield in the absence of DMS. h. Data in brackets are corrected based on water loss due to the maximum esterification reactions. n.a.: not applicable.

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40 T able 2 3 SOA formation from DMS photooxidation using an indoor chamber at RH=12% a Exp. NO x ppb DMS ppb g/m 3 OM g/m 3 OC DMS /V DMS OC DMS /OM DMS b Y DMS 100% c D 2 280 136 255 192 0.13 0.11 75 D 3 310 127 2 10 15 7 n.a. n.a. 7 5 D 4 210 170 11 4 73 0.14 0.12 64 D 5 43 1 16 12 2 65 0.14 0.12 5 4 a. Refe r to the super scripts in Table 2. b. OC DMS / OM DMS = OC DMS / V DMS / 1.2. T he density of the DMS aerosol is 1.2 g cm 3 OC DMS / V DMS value s ( g cm 3 ) were determined using an OC/EC analyzer and SMP S c A erosol yield for DMS. Y DMS = OM / DM S. The uncertainty for the single precursor SOA yield was 8%

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41 F igure 2 1 Ani on chromatogram of the aerosol sample of D 1 show ing MSA, MSIA and sulfate.

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42 F igure 2 2 Major acid (MSIA, MSA and sulfuric acid ) mass fraction of the total acidic aerosol mass in M 1, M 2 and D 1 (assuming MSIA, MSA and sulfuric acid are the only acidic aerosol products)

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43 F igure 2 3 x iso and Y DMS values associated with M 1 (IC data) compared to those with M 5 (OC/EC data). Experimental conditions of M 1 and M 5 are similar. x iso and Y D MS associated with OC/EC data are found in Table 2 2 and Y DMS as sociated with IC data is in Table 2 1. x iso associated with IC data =1 x DMS (Table 2 1).

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44 F igure 2 4 Isoprene SOA yields at different concentration of NOx or isoprene with and without DMS (A) Isoprene SOA yields at different NO x concentration with and without DMS (isoprene concentration=850 ppb and RH=12%). (B) Isoprene SOA yields at different isoprene concentration with and without DMS (NO x concentration=40 ppb and RH=12%). The isoprene SOA yield was calculated using eq. 2 4

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45 Figure 2 5 Isoprene SOA yields at different RH with and without DMS (A) Isoprene SOA yields at different RH with and without DMS ( initial isoprene concentration=850 ppb and NO x = 40 ppb ). (B) Isoprene SOA yield s at different RH with and without DMS ( initial isoprene concentration=850 ppb and NO x = 80 ppb ). The isoprene SOA yield ( Y iso ) was calculated using eq. 4 and t he percentage increase of isoprene SOA yield ( % Y iso ) due to DMS was marked in the figure with an estimated uncertainty

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46 Figure 2 6 Time profiles of aerosol growth and precursor decay for several experiments ( Exp. I 4 M 4 and D 5 ) (A) Time profiles of aerosol growth and isoprene decay for t he isoprene / NO x photooxidation with and without DMS (E xp. I 4 and M 4). (B) Time profiles of aerosol growth and the DMS decay for the DMS / NO x photooxidation (E xp. D 5)

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47 CHAPTER 3 STUDY OF THE EFFECT OF METHANESULFONIC A CID ON ISOPRENE SECONDARY ORGANIC A EROSOL FORMATION Background U nlike sulfuric acid, MSA has no clear anthropogenic sources so it is a convenient tracer of the photooxidation of DMS in the study of the sulfur cycle (Read et al., 2008) Ambient mon itoring of MSA in both the gas and the particle phase s has been widely conducted both in coastal and inland areas. For example, the gaseous MSA concentration in the eastern Mediterranean was reported to be in the range of 0.002~0.02 pptv and the particula te MSA concentration was from 19.6 to 75.5 ng m 3 (Mihalopoulos et al., 2007) From ambient samples in Riverside, CA, Gaston et al. (2010) found that up to 67% of the sub micrometer aerosol contained MSA MSA has also been found in the inland areas. For example, Lukas et al. has detected 31.5 ng m 3 MSA in the ambient air in Kpuszta, Hungry (Lukacs et al., 2009) The considera ble amount of aerosol phase MSA in the atmosphere may influence the secondary organic aerosol (SOA) formation through reactions with the atmospheric organic gases. Sulfuric acid is one of the major DMS products and it has been known to increase secondary organic aerosol (SOA) production through the heterogeneous reactions of carbonyls, form ing oligomers (Czoschke et al., 2003; Edney et al., 2005; Jang et al., 2002) and through the formation of organosulfates of 2 m ethyltetrols (Claeys et al., 2004) from epoxides (Minerath et al., 2009; Paulot et al., 2009; Froyd et al., 2010) MSA is also a major product from DMS

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48 photooxidation. H owever, to date the impact of MSA on SOA formation is un e xplored MSA is a strong acid with pKa = 2, so it c ould play a role similar to sulfuric acid (pKa = 3) in the increase of SOA mass through either catalyzing heterogeneous reactions of carbonyl co mpounds or forming MSA esters (organosulfonates) with organics. Additionally, researches have confirmed the acid catalyzed aqueous reactions in the SOA formation in cloud (Loeffler et al., 2006) or wet aerosol (Liggio et al., 2005) while high concentrations of MSA have been measured in cloud aerosols (Froyd et al., 2009) and espec ially in CCN (Langley et al., 2010) Therefore, MSA can be an important acidic source that could p robab ly modify the hygroscopicity of the SOA followed by the CCN number change, and makes the SOA influence on cloud albedo more complicated. In this study, the effect of MSA aerosol on isoprene SOA product ion via heterogeneous reactions of the gas phase organics from isoprene photooxidation was studied. The SOA mass with MSA w as compared to that without MSA using a Teflon film indoor chamber. T he influence of MSA on isoprene products distribution was inve stigated through analyzing the gas and particle phase products of isoprene photooxidation both with and without MSA using a gas chromatograph ion trap mass spectromet er (GC ITMS). T he resulting SOA mass y ields and the yields of the detected products in th e presence of MSA were compared to those in the presence of sulfuric acid.

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49 Experimental Section Chamber Experiments to Study th e Impact of MSA on Isoprene SOA M ass To study the impact of MSA on isoprene SOA mass, isoprene SOA was formed through photooxid ation of isoprene in the presence of NO x followed by nebulization of MSA. The mass of SOA before and after MSA nebulization was compared. Na 2 SO 4 seed aerosol was nebulized into the chamber before the formation of SOA to mimic the ambient condition where inorganic aerosol pre exists The detailed exp erimental conditions and resulting aerosol data are shown in Table 3 1 (Exp H 1 and L1 ). Chamber Exp eriment Procedure in Figure 3 1A The e xperiments were conducted using a 2 m 3 Teflon indoor chamber equipped with 16 UV lamps (Solarc Systems Inc., FS40T12/UVB) that cover the wavelengths between 280 900 nm Prior to each experiment, t he chamber was flushed using air from clean air generators (Aadco Model 737, Rockville, MD; Whatman Model 75 52, Haverhill, MA). To generate isoprene SOA, isoprene and NO x (99.5% nitric oxide, Linde Gas) were in troduc ed into the chamber using a syringe through the injection ports. A 16mM Na 2 SO 4 solution was nebulized into the chamber as preexisting neutral seed aerosols. Humidity was controlled at 70%, so Na 2 SO 4 (E fflorescence RH=56%) seed aerosol remained as the liquid phase. UV lamps were turned on when concentrations of the injected chemicals were stabilized (see Table 3 1 for initial concentrations of isoprene, NO x and seed a erosol) and turned off after 2 hour s

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50 10 minutes later when the photochemical reactions fully stopped, MSA aerosol was nebulized to the chamber to evaluate the MSA effect on isoprene SOA mass increase. A erosol Water Content In order to calculate the SOA mass, the measurement of the water content in the MSA aerosol is need ed. The resulting aerosol water content is applied to SMPS data to estimate the organic mass contributed solely by the isoprene SOA (se e section 3.2). To determine t he water content in MSA aerosol MSA aerosol was impacted on a silicon window followed by a Fourier transform infrared spectrometer (FTIR, Nicolet Magma 560, Nicolet) analysis The detail ed description for measuring the wate r content in aerosol using the FTIR technique can be found in the previous study by Jang et al. (2010) Characterization of Isoprene SOA Products (Figure 3 1B and 3 1C) Generation and S ampling of I soprene SOA To study the influence of MSA on the gas particle distribution of isoprene oxidation not only was isoprene SOA externally mixed with MSA aerosol (Figure 3 1B) but also isoprene SOA was produced in the presence of DMS (Figure 3 1C). Table 2 list s the conditions of the experiments for product analys e s in the presence and absence of MSA aerosol The indoor chamber experimental procedures are the similar to those mentioned in section 2.1 Chamber experiments for photochemical reactions of isoprene in the presence of NO x either with DMS (Figure 3 1C) or without DMS (Figure 3 1B) were operated for 1.5 hours under the low RH (25%) to

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51 reduce the wall loss of semivolatile gaseous product s At the end of the SOA experiment, UV Visible lamps were tuned off for the isoprene SOA produced without DMS (Figure 3 1B) and 10 minutes later, the diluted MSA aqueous solution was ato mized into the chamber. For the isoprene SOA produced with DMS (Figure 3 1C), UV Visible lamps were on over the course of the experiments. Analytical P rocedure for I soprene SOA P roduct C haracterization The gas and the particle samples were collected using a filter/filter/denuder (coated by XAD 4 resin) sampling train (Kamens et al., 1995) for 50 minutes. Immediately after sampling the chamber air using the filter/filter/denuder train bornyl acetate a s an internal standard w as added to the filter samples (aerosol) and denuder samples (gas) The filter samples were then extracted using acetonitrile (optima grade) in a microsoxhlet ( Fisher Scientific ) and the denuder samples were extracted using a mixtu re of acetonitrile and methylene chloride (optima grade). Further descriptions of sample extraction procedures and derivatization methods for carbonyls (O (2,3,4,5,6 Pentafluorobenzyl) hydroxylamine hydrochloride PFBHA ) and for alc o hols (N,O bis(trimethy lsilyl) trifluoroacetamide BSTFA) can be found elsewhere (Jang and Kamens, 1999) All the treated samples were analyzed by a gas chromatograph ion trap mass spectrome ter ( GC ITMS Varian model CP 3800 GC, Saturn model 2200 MS) with a 30m capillary column ( ID=0.25mm, Varian, Factor Four VF 5ms CP8944 ) using the temperature program as follows: 80 o C for 1 min; ramp to 100 at 5 o C min 1 ; hold for 3 min; ramp to 280 o C at 10 o C min 1 and hold for 8 min. F our levels of external

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52 standard solutions containing six different carbonyl co mpounds (trans 2 hexenal, acrolein, methacrolein trans 2 methyl 2 butenal glyoxal and methylglyoxal) and one alcohol compound (butane 1,2,3,4 tetrol) in acetonitrile were used for calibration The detailed calibration procedures can be found elsewhere (Im et al., 2011) Results and Discussion SOA Yield I ncrease in the Presence of MSA Aerosol To study the impact of MSA on isoprene SOA mass increase the isoprene SOA mass before MSA aerosol nebulization was compare d with that after MSA aerosol nebulization. Figure 5 2 shows the time profile of aerosol volume concentration before and after MSA nebulization. The isoprene SOA mass concentration right before the nebulization of MSA ( the point A in Figure 2), M SOA,A w as calculated using the following equation: ( 3 1 ) where V A is the total aerosol volume concentration ( cm 3 m 3 ) V seed,A is the seed aerosol volume concentration ( cm 3 m 3 ) estimated by the initi al seed mass and the aerosol wall loss (assuming that the first order decay rate constants are a function of particle size (Mcmurry and Grosjean, 1985) and A (1.95 g m 3 ) is the aerosol density measured before introducing MSA aerosol into the chamber. The isoprene SOA mass concentration after the nebulization of MSA, M SOA,B is calculated by subtracting the seed aerosol mass and the nebulized MSA mass (MSA+water) from the total aerosol mass. ( 3 2 )

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53 whe re V B (total aerosol volume concentration ), V seed,B (seed aerosol volume concentration ) and B (aerosol density, 1.90 g cm 3 ) are measured about 10 minutes after introducing acidic aerosol into the chamber (all corresponding to the point B in Figure 2 ). M acid is the mass of acid in the aerosol measured using PILS IC The water mass fraction ( w ) of the total acidic aerosol (water + acid) mass, was calculated to be 0.14 at RH=25% and 0.62 at RH=70% for MSA. The term express es the sum of the MSA and water mass in the MSA aerosol at a given RH. The isoprene SOA yield ( Y iso,1 ) without acid normalized by the mass ( M seed, 1 )of Na 2 SO 4 seed before acid nebulization is calculated as follows: ( 3 3 ) The isoprene SOA yield increase ( Y iso, 2 1 ) due to acid, normalized by the mass ( M seed,2 )of nebulized acid is calculated as follows: ( 3 4 ) Table 3 1 summarizes Y iso,1 / M seed,1 and Y iso,2 1 / M seed,2 values under two different levels of MSA aerosol mass (6.1 and 5 3 g m 3 ) Y iso,1 / M seed,1 was 13.9x10 5 with the higher MSA aerosol mass (5 3 g m 3 Exp H1 ) and 42.7x10 5 with the low er MSA aerosol mass ( 6.1 g m 3 Exp A1). A s control experiment s Na 2 SO 4 aerosol was used instead of MSA aerosol to test the effect of the neutral inorganic aerosols on the Y iso, 2 1 / M seed, 2 Y iso, 2 1 / M seed, 2 was 1.7x10 5 for the higher Na 2 SO 4 mass level (Exp H3 ) and 14.2x10 5 for the lower Na 2 SO 4 mass level (Exp L3 ) Our results showed that Y iso, 2 1 / M seed, 2 values with MSA aerosol are significantly higher than those with

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54 neutral Na 2 SO 4 aerosol, thus indicating that the MSA aerosol more likely promote s SOA growth through acid catalyzed heterogeneous reactions of the isoprene SOA products In comparison, Y iso, 2 1 / M seed, 2 was also measured for the two d ifferent levels of H 2 SO 4 aerosol mass (5.8 and 50.1 g m 3 ): 15.7 x10 5 for the higher sulfuric acid mass (Exp H2 ) and 102.4x10 5 for the lower sulfuric acid mass (Exp L2 ). Since the Y iso,1 / M seed,1 values for all the experiments in Table 3 1 are similar w ithin error range, the result of Exp H2 can be compared with that of Exp H1 and similarly the result of Exp L2 can be compared with that of Exp L1. Interestingly, Y iso,2 /M acid values for the nebulization of low concentration acid (Exp L1 and L2) are muc h higher than those for the nebulization of high concentration of acid (Exp H1 and H2). The reason is that when nebulizing the low concentration acid, the amount of aerosol growth due to the aerosol phase water chemistry (including absorbing gaseous organ ics and further reactions with acid) per unit acid mass is much larger than that when nebulizing the high concentration acid. That is to say, Exp H1 and H2 with the nebulization of high concentration of acids provide more reliable results than Exp L1 and L2. Therefore, judging from Exp H1, H2 and H3 which have similar conditions, MSA may have a roughly similar effect on isoprene SOA mass increase compared with H 2 SO 4 Product A nalysis on the I soprene SOA with and without MSA U sing GC ITMS. T o further inves tigate the mechanism of MSA impact on aerosol phase reactions the gas and the particle phase products of isoprene photo oxidation both

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55 in the presence and the absence of MSA were also analyzed using GC ITMS. Twelve oxidation products ( PFBHA derivatives: P1~P11, BSTFA derivative: P12 ) reported in the literature were identified in this study (Table 3 3 ). Seven of them were tentative ly identified. Figure 3 3 shows the r econstructed ion chromatogram of P1~P11 based on m/z = 181 peak. Figure 3 4 shows the m ass spectra of derivatives of P1~P12. The product y ield which is defined as the product concentration divided by the consumed isoprene concentration ( ROG in Table 3 2) was shown in Figure 3 5 for both gas and particle products. Product yields of the ph otooxidation of isoprene/NO x are compared to those from photooxidation of the isoprene /NO x +MSA system. F or the yield s of the detected gas phase carbonyl product s of isoprene photooxidation (Figure 3 5B) n o significant difference appeared between the two s ystems, suggesting that isoprene photooxidation in the gas phase is not significantly changed by the presence of acidic aerosols. In contrast, several aerosol phase carbonyl compounds (determined from filter sampling) were found to have much higher yield s (>500% increase) in the presence of acid ic aerosol: e.g. methacrolein (P1), methyl vinyl ketone (P2), glyoxal (P8) and methylglyoxal (P9). The higher aerosol phase yields of these carbonyl products in the presence of MSA ( isoprene/NO x +MSA system in Figu re 3 5 A suggest s that oligomerization in aerosol is accelerated by MSA as an acid cataly st These oligomers originated from carbonyls return to their parent compounds during the analytica l workup procedure and apparently increase their concentrations in G C ITMS analyses (Czoschke et al.,

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56 2003; Healy et al., 2008) Within statistical errors based on analytical data, other carbonyl compounds (P3~P7 and P10~P11) do not show a significant difference between aerosol ph ase product yields with MSA and those without MSA. The yield of 2 methyltetrol (P12) was also significantly increased by the presence of MSA. Gaseous e p oxydiols from isoprene photooxidation have been proposed to be the precursors of organosulfate of 2 m ethyltetrol which is enhanced by aerosol acidity (Paulot et al., 2009; Froyd et al., 2010) The organosulfate of 2 methyltetrol is converted to 2 methyltetrol through the reverse reaction during the analytical wo rkup process In our study the increased yield of methyltetrol was in the presence of MSA compared with in the absence of MSA suggest s that MSA may react with epoxydiol s forming methanesulfonate. The product yields in the isoprene/NO x +H 2 SO 4 system and the isoprene/DMS/NO x are also shown in Figure 3 5 A The s imilar trend in the product yield increase was observed for P1, P2, P8, P9 and P12 among the isoprene/NO x +MSA, isoprene/NO x +H 2 SO 4 and isoprene/DMS/NO x systems. The result from product analysis further confirms that aerosol phase heterogeneous reactions of the carbonyls and epoxides, which are accelerated by H 2 SO 4 may also be accelerated with MSA. Conclusion and Atmospheric Implication T he chamber data of this study suggest s th at MSA will increase isop rene SOA production through heterogeneous reactions of gaseous organic compounds in acidic aeroso l although t he aerosol composition of the chamber produced SOA can

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57 be different from the ambient isoprene SOA due to the differences in gas compositions, react ion time, light spectrum, and light intensity. Also in this study, the relative effect of MSA on SOA mass growth was found to be around 30% lower per unit mass as compared to H 2 SO 4 This value may be applied to estimating the relative contribution of MSA and H 2 SO 4 to the enhancement of SOA mass in the ambient. The estimation of the relative contribution of MSA and H 2 SO 4 to the increase of SOA mass in the ambient also requires the knowledge of mass ratio of the two acids in aerosol. The mass ratio in the ambient is much lower than the experiment value (3.86 calculated from acid mass of C3 and C4 in Table 3 2) due to the low NO x concentration in the ambient that reduces MSA formation (Barnes et al., 1988) and high contribution of H 2 SO 4 from anthropogenic SO 2 In the ambient data of this study, the highe st methanesulfonate/non seasalt sulfate value is 0.134. Thus, assuming that MSA is similarly efficient than H 2 SO 4 in increasing the SOA mass, the estimated contribution to SOA mass increase from MSA in this scenario could be 1 5.5 % of that from H 2 SO 4 In the long run, the global SO 2 emission is going to be und er control so the H 2 SO 4 production in ambient aerosol is expected to be reduced. Meanwhile, the MSA production will be probably unchanged due to its natural origin, so the MSA contribution to the increase of SOA mass production through enhancing the heter ogeneous chemistry is expected to play a more important role especially in seaside areas.

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58 Table 3 1 Isoprene SOA yield due to sodium sulfate aerosol, MSA aerosol or sulfuric acid aerosol a a. Temperature was 23~25 o C and RH was 69%~73%. The estimated uncertainty of each experiment is calculated from the errors associa ted with SMPS (2%), PILS IC ( 6 % for high aerosol mass injection and 15 % for low aerosol mass injection ), aerosol density (5%) and wall loss correction for seed aerosol (10%). b. The aqueous solu tion concentration for Exp L 1, L2 and L3 is 0.16 mM and that for Exp H1 H2 and H3 is 1.6 mM. All the reported data are the mass in the aerosol phase. c. See Eq. 3 1 and 3 2, Figure 3 2 and text in section 3.2 for the isoprene SOA mass before and after aci d nebulization d. See Eq. 3 3 and Eq. 3 4 in the text. e. The concentrations of the nebulized H 2 SO 4 and Na 2 SO 4 were calculated based on the sulfate ion mass which was determined by subtracting the sulfate mass in the seed aerosol (determined using initia l seed aerosol mass, wall loss rate and the time elapsed) from the total sulfate ions mass measured using PILS IC after H 2 SO 4 or Na 2 SO 4 nebulization. Exp M seed, 0 ( Initial) g m 3 Initial isoprene ppb Initial NO x ppb consumed isoprene g m 3 M seed,1 before acid nebulization) g m 3 M acid (nebulized) g m 3 b c M SOA,1 g m 3 M SOA,2 g m 3 Y iso,1 /M seed,1 x10 5 d iso,2 1 /M acid x10 5 d species concentration H1 245 4470 290 505 0 133.9 MSA 53 32.2 69.5 4.8 0.6 13.9 1.9 H2 22 7 4450 300 548 0 106.9 H 2 SO 4 50.1 e 27.5 70.6 4.7 0.6 15.7 2.4 H3 163 4760 292 617 0 71.1 Na 2 SO 4 72.2 e 24.6 32.4 5.6 0.7 1.7 0.3 L1 18 5 507 0 230 641 2 80.5 MSA 6. 1 24.7 41.4 4.8 0.6 42.7 6.4 L2 3 60 4580 285 6530 163.4 H 2 SO 4 5.8 e 54.2 93.0 5.1 0.6 102.4 24.9 L3 21 3 4480 290 6 600 118.1 Na 2 SO 4 8 e 39.8 47.3 5.1 0.6 14.23.5

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59 T able 3 2 Initial chamber conditions of the experi ments used for product analysis a. Exp System Initial isoprene ppb Initial DMS ppb Initial NO x ppb Acid mass b. g m 3 MSA H 2 SO 4 B1 Isoprene/NO x + H 2 SO 4 4840 0 350 0 1 9 .6 B2 Isoprene/NO x + MSA 5 191 0 2 88 50.0 0 C1 Isoprene/NO x 4716 0 360 0 0 C2 Isoprene/NO x 4800 0 353 0 0 C3 Isoprene/DMS/NO x 4182 1250 315 117.9 30.5 C4 Isoprene/DMS/NO x 4960 1200 362 125.3 32.5 a. Temperature was 24~27 o C and RH was 23%~26%. The estimated uncertainty of each experiment ( 8%) is calculated from the errors associated with SMPS (2%) aerosol density (5%) and ROG iso (6%) To obtain enough aerosol mass for analysis, aerosol sample from Exp C1 was combined with that from Exp C2, and same thing was done for Exp C3 and C4. b. The acid was introduced either through nebulization of MSA or H 2 SO 4 solution (Exp B1~B 2) or the photooxidation of DMS (Exp C3~C4).

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60 T able 3 3 Relative intensities of CI and E I mass spectra for PFB HA derivatives of isoprene photooxidation products Product ID Product Name a Retention time min MW b CI EI M+1 M 197 M M 1 181 M+181 M 181 M 197 M 225 P1 m ethacrolein 10.78, 10.85 265 100 1.4 13 5 100 8 2 1 P2 m ethyl vinyl ketone 10.99, 11.05 265 100 5 2 3 5 5 100 0.4 1.5 5 0.8 P3 3 methylbut 3 en al 11.95,11.98 279 100 1.3 13 100 45 1.5 1.2 P4 2 methylbut 3 enal 12.77, 12.85 279 100 6 14 100 0.3 3 0.3 1.5 P5 h ydroxyacetone 13.39 269 100 3 0. 7 100 0.2 0.4 10 0.4 P6 pent 4 en 2 one 13.72 279 100 30 1.5 10 100 5.5 1 1.6 P7 1 hydroxy 3 methylbut 3 en 2 one c 14.15, 14.57, 14.70,14.87 295 100 3 7.5 100 7.5 10 1 P8 Glyoxal 20. 01, 20.11 448 d 100 8 100 0.7 3.5 P9 m ethylglyoxal 20.18, 20.49 462 d 100 3 2 100 0.9 21 0.1 P10 2 oxopropanedial 20.85, 20.96, 21.20, 21.23 476 d 10 0 5.5 3 100 2.5 20 P11 2,3 dioxobutanal 23.03, 23.16, 23.45, 23.64 685 e 5 100 3 a. P1, P2, P5, P8 and P9 are named using common nomenclature and the rest of the products are named using the IUPAC nomenclature (recommendations 1993). P3, P4, P5, P6, P7, P10 and P11 are tentatively identified b. The molecular weight of a PFBHA derivative increases the molecular weight of an underivatized compound by 195 c. P7 includes several structural isomers due to the position of an OH functional group so the name given here is one of its possible structures. d. The compound is di derivatize d. e. The compound is tri derivatized (its M is outside the scanning range so its major CI fragments were not shown)

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61 F igure 3 1 Chamber e xperiment procedures to study the impact of MSA on isoprene SOA growth (Figure 3 1A for Exp A1~A6 ). Chamber exper imental procedures to characterize isoprene SOA products (Figure 3 1 B for Exp B1~B2 and Figure 3 1 C for Exp C1~C4). MSA in the figure may be switched to H 2 SO 4 or Na 2 SO 4 depending on a specific experiment. The F/F/D indicates the sampling system comprisin g filter/filter/denuder for the isoprene products analysis.

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62 Figure 3 2 The time profile of aerosol volume concentration (before wall loss correction) measu r ed by SMPS for Exp H1 The time profile was used to calculate M SOA ,1 and M SOA ,2 of the experim ents in Table 3 1.

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63 Figure 3 3 Reconstructed m/z = 181 ion chromatogram in the EI mode for PFBHA c arbonyl derivatives o riginated from isoprene oxidation (both gas and particle phase products in the presence and in the absence of acids). The C notes for c ontamination peaks determined by comparing isoprene oxidation data to background air data U nlabeled peaks are unknown peaks.

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64 Figure 3 4 GC ITMS m ass spectra (relative intensity vs. m/z) in the EI mode for PFBHA (P1~P11) derivatives of carbonyl pro ducts and BSTFA (P12) derivatives of 2 methyltetrol originated from isoprene photooxidation in the presence of NO x P1~P11 were found in both gas and particle phase both in the presence and in the absence of acids and P12 was detected only in the particle phase.

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65 Figure 3 5 Aerosol phase product yield s (A) and gas phase product yield s (B) determined using GC ITMS analys e s for isoprene/NO x isoprene/DMS/NO x isoprene/NO x +MSA and isoprene/NO x +H 2 SO 4 A erosol phase product yield s were corrected for wall l oss. Tentatively identified carbonyl products (P1~P11) are summarized in Table 3 P12 denotes 2 methyltetrol. The standard error ( SE s ) of the measured mass ( g) of each compound was obtained through three replica experiments for the PFBHA derivatization of hexanal in different concentration levels using the same analytical procedure used for aerosol product analysis SE s ( g) as a function of hexanal mass ( mas s s g) is expressed as The equation for SE s and the measured mass of each compound was applied to the estimation of standard errors of the concentration of the carbonyl compound.

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66 CHAPTER 4 CHAMBER SIMULATION OF PHOTOOXIDATION OF DIMETHYL SULFIDE AND ISOPRENE IN THE PRESENCE OF NO X Background The Intergovernmental Panel on Climate Change (IPCC) has classified the aerosol originat ing from DMS as one of the most important components that needs to be better understood in the planetary climate system (IPCC, 1995) The DMS photooxidation mechanism is an important factor for understand ing the role DMS plays in the earth sulfur cycle and climate system so it has been studied by many researchers (Barnes et al., 2006; Turnipseed, 1993; Urbanski and Wine, 1999; Yin et al., 1990b) Despite all the efforts exerted to understanding atmospheric DMS chemistry, a large discrepancy still exists between the ambient measurement s of DMS products and the simulation results for compounds such as DMSO (Chen et al., 2000) H2SO4 and MSA (Lucas and Prinn, 2002a) The poor predictability of the kinetic model for the formation of DMS pr oducts was caused by uncertainties in the rate constants of DMS reactions in the gas phase, the lack of aerosol phase reactions of the DMS products, and missing information regarding the impact of volatile organic compound s (VOC) on the DMS photooxidation through both the gas and the particle phases. I n the presence of UV light, DMS oxidation is initiated by OH radical reactions through both the hydrogen (H) abstraction reaction and the addition reaction (Atkinson et al., 1989) It is known that DMS also reacts with O( 3 P), NO 3 (Atkinson et al., 1989) and NO 2 (Balla and Heicklen, 1984) The updated mechanisms and rate constants of the DMS initial reactions and sequential reactions have been included in Table S1 3 of the supplementary materials. For example, the rate constant (s 1 molecules 1 cm3) for the OH radical abstraction reaction of DMS (No. 59) was suggested to be 1.13 x10 11 exp( 254/T) by Atkinson et al. (1997) ; the rate constant for the OH radical addition reaction to

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67 DMSO (No. 2) was updated to 6.1 x10 12 exp(800/T) (Sander, 2006) Two other initial reac tions of DMSO oxidation (No. 1 and 3) were newly added (Sander, 2006) The change of the reaction rate constants may influence both the prediction of the DMS decay and its pr oduct distribution. M issing aerosol phase reactions in the DMS mechanism is another reason why several important DMS products such as MSA and H 2 SO 4 h ave been underpredicted using the existing model. Recent field studies indicate that the heterogeneous re actions of DMS products significantly contribute to the formation of MSA in the aerosol. For example, in a field study in the equatorial P acifi c, Davis et al. (1999) indicated that the production of MSA through g as to particle partitioning accoun t f or only 1% of the observed aerosol phase MSA. Similarly, through an eastern Mediterranean campaign, Mihalopoulos et al. (2007) suggested that a t least 80% of the production of aerosol phase MSA may be due t o heterogeneous reactions of DMS photooxidation products (possibly DMSO). Bardouki et al. (2002) confirmed that the liquid phase reactions of DMSO and MSIA with OH radicals produce MSA with high yields. To better predict the atmospheric fate of DMS, the development of an advanced kinetic model is needed. The failure to consider the impact of VOC on the DMS photooxidation also affects for DMS oxidation pro ducts in ambient studies. In a recent indoor chamber study Chen and Jang (2012a) discovered that the MSA produc tion from DMS photo oxidation is affected by the presence of isoprene. However, kinetic studies of the impact of coexisting VOCs on DMS chemistry are inadequate. In this study, a new DMS kinetic model was developed by including not only the most recently reported reactions and their rate constants but also the heterogeneous reactions of DMS gaseous products on the surface of aerosol The model was first tested for the DMSO photooxidation in the presence of NOx using a 2 m 3 indoor chamber

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68 because the DMSO is one of the important product s of the DMS photooxidation. The decay of DMSO major gaseous products [e.g, dimethyl sulfone (DMSO 2 ), SO 2 NOx and O 3 ] and aerosol products (e.g., MSA and sulfuric acid ) were simulated using the new kinetic model integrate d with the Morpho chemical solver (Jeffries, 1998) The resulting DMSO mechanism s have been incorporated into the kinetic mechanisms for DMS photooxidation with a few adjustments on the rate constants of the DMS related reactions. To study the influence of atmospheric VOCs on DMS oxidation, t he new DMS photoxidation model, coupled with the isoprene photooxidation model usin g the Master Chemical Mechanism (MCM) v3.2 ( http://mcm.leeds.ac.uk/MCM/ ), was also simulated for the chamber data. Experimental Section Indoor Teflon film Chamber Experiments of DMS O and DMS P hotooxidation Experiment P rocedures Since the DMSO oxidation mec hanism is an important subset of the DMS oxidation mechanism, five DMSO/NO x experiments were conducted to validate the DMSO submodel. The e xperiments were operated using a 2 m 3 Teflon indoor chamber equipped with 16 UV lamps (Solarc Systems Inc., FS40T12/ UVB) cover ing the wavelengths between 280 and 900 nm The chamber was flushed using air from clean air generators (Aadco Model 737, Rockville, MD; Whatman Model 75 52, Haverhill, MA). DMSO was added to the chamber by passing clean air through a T union w here DMSO (99.6%, Sigma Aldrich) was injected using a syringe and gently heated using a heat gun. NO x (99.5% nitric oxide, Airg as) was injected into the chamber by inserting a syringe through the injection ports. When the initial concentration of NO x was stable, UV lamps were turned on.

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69 The procedures of the DMS/NO x experiments were same as those of the DMSO/NO x experiments except that DMS (99.7%, Aldrich) was injected in to the chamber using a syringe without heating. The detailed experimental conditions for DMSO and DMS photooxidation reactions are summarized in Table 4 1. Instrumentation and Sample Analysis The concentration s of DMS, SO 2 NO x and O 3 in the chamber w ere measured using an HP 5890 g as c hromatography f lame i on ization d etector (GC FID) a fl uorescence TRS analyzer ( Teledyne Model 1 0 2 E) a chemiluminescence NO/NO x analyzer (Teledyne Model 200E) and a photometric ozone analyzer (Teledyne model 400E) Particle concentrations were measured using a s canning m obility p article s izer (SMPS, TSI, Mod el 3080, MN) combined with a condensation nuclei counter (CNC, TSI, Model 3025A). A particle into liquid sampler (Applikon, ADI 2081) coupled with an ion chromatography ( Metrohm, 761 Compact IC ) (PILS IC) w as used to measure the major aerosol products (MS A and H 2 SO 4 ) produced from DMS photooxidation. The detection limit of PILS IC is 0.1 g m 3 and the associated error is 10 %. DMSO and DMSO 2 were collected using a liquid N 2 ( ~ 195 o C) trap for 8 10 minutes at a flow rate of 3 L min 1 3 mL of Acetonitrile (optima grade) with deuterated DMSO ( d 6 DMSO, used as an internal standard) were the n added to the trap which was subsequently capped and immersed into hot water (~60 o C) for 10 minutes. The liquid in the trap was then transferred to a small via l for chromatograph y ion trap mass spectrometer (GC ITMS Varian model CP 3800 GC, Saturn mod el 2200 MS) analysis. The analysis of DMSO and DMSO 2 in solution using GC ITMS has been presented by Takeuchi et al (2010) The GC temperature profile in our study is 70 o C for 1 min; ramp to 90 o C at 5 o C min 1 ; ramp to 280 o C at 20 o C min 1 and hold for 8 min. Figure A 1 in

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70 Appendix A summarizes the retention time and mass spectra of DMSO, DMSO 2 and d 6 DMSO. Indoor Teflon film Chamber Experiments of DMS photooxidation in the P resence of I soprene Isoprene was i njected into the chamber together with DMS to study its impact on DMS aerosol formation. In addition to the chemicals monitored in the DMS/NO x experiments, major isoprene photooxidation products were sampled every 30 min ( 1 0 minutes sampling) for 2.5 hour s ( 5 samples in total ) with a flow rate of 1.0 L min 1 using an impinger that contained 12 mL of acetonitrile with Bornyl Acetate (internal standard) Prior to each photoirradiation experiment, the chamber background air was analyzed for potential contami nation. Further descriptions of derivatization methods for carbonyls (O (2,3,4,5,6 Pentafluorobenzyl) hydroxylamine hydrochloride PFBHA ) can be found elsewhere (Im et al., 2011) All the impinge r samples were ana lyzed by the GC ITMS with the temperature program as follows: 80 o C for 1 min; ramp to 100 at 5 o C min 1 ; hold for 3 min; ramp to 280 o C at 10 o C min 1 and hold for 8 min. Information for p roduct quantification can be found elsewhere (Im et al., 2011) Results and Discussion Kinetic Model Reaction m echanisms of DMS DMS photooxidation in the presence of NO x in the indoor chamber was simulated using explicit kinetic mechanisms integrated with the Morpho kinetic solver Table A 1 ~ A 3 (in Appendix A ) summarize the kinetic mechanisms related to DMS oxidation along with their reaction rate constants, which were collected from the recent literature The reaction rate constants of the oxidation for the non sulfur compounds (e.g., formaldehyde, methanol, and methane, etc) are obtained from the MCM mechanism s

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71 Formation of MSA and H 2 SO 4 through heterogeneous reactions of gaseous DMS oxidation products One of the major limitations of the existing explicit model for DMS photoox idation is the missing heterogeneous chemistry for DMS oxidation products in aerosol phase In the model of this study we assumed that DMSO produces methanesulf i nic acid (MSIA), which consequently forms MSA in the aerosol phase (Bardouki et al., 2002) and DMSO 2 produces H 2 SO 4 through heterogeneous reactions (Koga and Tanaka, 1993) In order to in clude h eterogeneous reactions of gaseous DMS oxidation products, the r ates of sorption ( k ad cm 3 molecules 1 s 1 ) and desorption ( k des s 1 ) of the gaseous organic compounds (Kamens et al., 1999) have been added to the new model The k ad / k des value is equal to the equilibrium constant, K p for the gas particle equilibrium of a given partitioning compound. ( 4 1 ) The n ucleation of gaseous MSA and sulfuric acid originating from DMS photooxidation produce s an aerosol mass suitable for partitioning of organic compounds. The mass of MSA and sulfuric acid are expressed as Aerosol in th is mechanism. The DMSO present in the gas phase is denoted as [ CH 3 S(O)CH 3 (g) ] In the same way t h e g as phase MSIA is denoted as [ CH 3 S(O)OH (g) ] and the gas phase DMSO 2 is denoted as [ CH 3 (O)S(O)CH 3 (g) ] The particle phase, DMSO MSIA and DMSO 2 are described as [ CH 3 S(O)CH 3 (p) ], [ CH 3 S(O)OH (p) ] and [ CH 3 (O)S(O)CH 3 (p) ], respectivel y The parti ti onin g process es of DMSO, MSIA and DMSO 2 are desc ribed as follows. CH 3 S( O)CH 3 (g) + Aerosol CH 3 S(O)CH 3 (p) + Aerosol @ ( k ad ) CH 3 S(O)CH 3 (p) CH 3 S(O)CH 3 (g) @ 1.7 ( k des ) CH 3 S(O)OH (g) + Aerosol CH 3 S(O)OH (p) + Aerosol @ ( k ad ) CH 3 S(O)OH (p) CH 3 S(O)OH (g) @ ( k des )

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72 CH 3 (O)S(O)CH 3 (g) + Aerosol CH 3 (O)S(O)CH 3 (p) + Aerosol @ ( k ad ) CH 3 (O)S(O)CH 3 (p) CH 3 (O)S(O)CH 3 (g) @ ( k des ) The reaction of heterogeneous oxidation of DMSO MSIA and DMSO 2 in aerosol are described as follows. CH 3 S(O)C H 3 (p) CH 3 S(O)OH (p) @ ( k r ) CH 3 S(O)OH (p) CH 3 SO 3 H @ ( k r ) CH 3 (O)S(O)CH 3 (p) H 2 SO 4 @ ( k r ) w here k r (s 1 ) is th e rate cons tant for each aerosol phase reaction. Isoprene ox idation mechanism The kinetic mechanisms of isoprene oxidation have been described using t he MCM v3.2 and compared to the data from two experiments (Exp iso 1 and 2 in Table 4 2) with different NO x concentrations. DMS M odel S imulation Chamber c haracterizat ion The photolysis rates of inorganic species and organic compounds were calculated using the chemical solver integrated with the wavelength dependent absorption cross sectional areas, quantum yields, and the chamber light intensity. The light spectrum in side the chamber was measured using a spectroradiometer (PAR NIR & UV PAR, Apogee). For the calibration of the light intensity inside the chamber, an NO 2 photolysis experiment was separately conducted under the nitrogen gas (99.95%) environment The deta iled description of the light characterization procedure can be found in the previous study (Cao, 2008) The chamber wall loss of oxidant gases such as O 3 and H 2 O 2 were determined t hrough several dark chamber experiments Their wall loss rate s are estimated using a

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73 first order rate constant (s 1 ): 2.5 10 5 for O 3 and 6.7 10 4 for H 2 O 2 T he wall loss rates of DMS ( s 1 ), SO 2 ( s 1 ), DMSO ( s 1 ) and DMSO 2 ( s 1 ) were also experimentally determined assuming the first order rate and applied to reaction mechanism s ( Table A 1 ~A 3) to compare the simulated results to the ex perimental data Table A4 compares the wall loss rates of different chemicals in this study and those in literature (Ballesteros et al., 2002; Qi et al., 2007; Yin et al., 1990a) For MSA and H 2 SO 4 pre dominantly present in aerosol, their wall loss was calculated using the aerosol data assuming the first order d e cay as a function of the aerosol size (Mcmurry and Grosjean, 1985) The background gases in the chamber, such as methane (1.8 ppm), formaldehyde (8 ppb) and acetaldeh yde (2 ppb), were included in the model simulation. The methane is ubiquitous with a constant concentration The concentrations of formaldehyde and acetaldehyde in the chamber were determined using GC IT MS integrated with PFBHA derivatization. DMSO photoo xidation Since the DMSO photooxidation mechanism is an important part of DMS photooxidation mechanism s before the evaluation of the DMS photooxidation model, the DMSO submodel was evaluated. Five DMSO photooxidation experiments (Exp DMSO 1 DMSO 5 in Tabl e 4 1) were conducted to confirm the DMSO submodel. The model simulation of DMSO decay, the profiles of DMSO 2 SO 2 NO x and O 3 agreed with observations (Exp DMSO 1 and 2 in Figure 4 1). Without including the heterogeneous reactions (Eq. R .4 1 ~ R .4 9), MSA concentration s are significantly underestimated. As an example, the simulation s versus observation (Exp DMSO 1 and 2) before and after including the heterogeneous reactions are shown in Figure 4 2. Figure s A 2 and A 3

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74 summarize the corresponding informa tion for Exp DMSO 3 5 in Table 4 1. T he profiles of NO x O 3 and SO 2 were not influenced by the heterogeneous reactions. DMS photooxidation The DMSO submodel that contains heter ogeneous reactions of DMS products is included in the DMS oxidation mechanism. T he new DMS model was simulated against f ive DMS photooxidation experiments. In the model of this study the reaction of DMS with the CH 3 S radical, the decomposition of the CH 3 SO 3 radical, and the reaction of the CH 3 (O)S(O) radical with NO 2 were also i ncluded. These reactions h ave b e en either missed or assigned with improper estimate s of reaction rate constants in the existin g models The prediction of DMS decay and DMS product formation are improved after modification of the reactions. Barnes et al. (1988) proposed the DMS + CH 3 S reaction in order to explain the fast decay of DMS in the presence of NO x It was found that without this reaction, the model simulation of DMS decay is systematically slower than observa tion. T he DMS + CH 3 S reaction (Reaction No. 103 in Table A4 2) was thus added to the model with an estimated rate constant so that the decay of DMS and the profiles of NO x and O 3 of the simulation result could be best fitted to that of observation in our study The reaction rate constant of decomposition of the CH 3 SO 3 radical (reaction No. 46 in Table S1) was previously estimated to be 0.16 s 1 without experimental confirmation (Yin et al., 1990b) In this study, it was found that the change of this rate constant does not significantly influence the DMS decay or the NO x profile ; rather, it impacts the distribution of H 2 SO 4 and MSA. A value of 0.04 s 1 was found in this study to best fit the measured concentrations of aerosol phase H 2 SO 4 and MSA. The rate constant of the reaction between the CH 3 (O)S(O) radical and NO 2 (reaction N o. 24 in Table A4 1) was reported to be (2.2 1.1) x10 12 cm 3 molecule 1 s 1

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75 (Ray et al., 1996) with one standard deviation of error. In this study, a value of 5x10 13 ( within two standard deviation of error of Ray s data) was found to best fit the S O 2 and acid formation profile. The major ga seous products of DMS oxidation were simulated and are shown in Figure 4 3 A (for Exp DMS 3 5) and Figure A4 A (for Exp DMS 1 and 2). In general, SO 2 and DMSO 2 were reasonably predicted. The measured DMSO concent rations in the experiments containing DMS were not reported in this study (see The artifacts of DMSO measurement in the presence of DMS section in the supplementary materials). For aerosol phase products t he model underestimated the concentrations of MS A and H 2 SO 4 by up to a factor of three during the first 60 minutes of ch a mber experiments but simulate d close r to the measurement s during the rest of the experiments (Figure 4 3C and Figure A 4 C) In the model, heterogeneous reactions associated with DMS O, MSIA, and DMSO 2 are controlled by partitioning process es that are governed mainly by the aerosol mass. However, in the early stage of the experiment, aerosols are small because they are formed via nucleation so their surface area would be much more im portant than their mass in the partitioning processes s limit the accommodation of DMSO, MSIA, and DMSO 2 due to the mass based partitioning processes in the model Consequently, the production of MSA and sulfuric acid in the early stage of the chamber experiment s wa s underpredicted in the model of this study. Impact of the C oexisting I soprene on DMS P hotooxidation Isoprene p hotooxidation The MCM v3.2 includes comprehensive isoprene photooxidation mechanisms including some very rece ntly proposed mechanisms such as ep o xide formatio n (Paulot et al., 2009) The i soprene model was simulated ag a inst Exp iso 1 and 2 The major products [e.g., methacrolein (P1), methyl vinyl ketone (P2), glyoxal (P3), and

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76 methylglyoxal (P4) ] originat ing from is o pr e ne were also simulated and compared to the experimentally measured con c entrations The mass spectra data for isoprene major gaseous products are summarized in Figure A 5 and the simulation results are illustrated against observation in Figure A 6. Overall, the MCM mechanism predicts the isoprene decay, the formation of s everal isoprene products, and the profiles of NO x and O 3 well. DMS P hotooxidation with Coexisting Isoprene Exp eriments iso DMS 1, iso DMS 2 and iso DMS 3 were carried out under similar initial concentration s of DMS and NO x The simulation profiles of DMS, isoprene, MSA and H 2 SO 4 are shown in Figure 4 4 in comparison with the measurement s The concentrations of NO x O 3 and the gas phase products (P1 P4) originating from isoprene oxid ation are well predicted using the kinetic model ( Figure A 7). To understa nd the impact of isoprene on the production of MSA and H 2 SO 4 molar yields (defined as the amount of a produced product divided by the amount of the consumed DMS) of MSA and H 2 SO 4 were compared between experiments with different initial isoprene concentrat ion s with similar amount s of DMS consumption The yields of MSA and H 2 SO 4 (in Table 4 3) were found to increase as the initial isoprene increases for both the model simulation and experimental data (after correction for wall loss and chamber dilution). To understand the impact of isoprene on yields of MSA and H 2 SO 4 the contribution of gas phase reactions and aerosol phase hetero geneous chem istry of DMS photooxidation to the formation of MSA and H 2 SO 4 were analyzed using the integrat ed reaction rate (IRR ) as shown in Table 4 3. The integrated reaction rate, expressed as an accumulated flux of chemical formation or consumption at a given reaction and an initial concentration, is estimated using the Morpho chemical solver. Overall the IRR values of

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77 the f ormation of both MSA and H 2 SO 4 increase with the increasing initial isoprene concentration. The IRR analysis suggest s that higher initial isoprene concentration s enhance the formation of SO 2 consequently increasing the production of sulfuric acid. The IR R ( Table A4 5 ) of DMS with O( 3 P) was found to be the major variant among the experi m ent s with different levels of isopr e ne conce n tration. T he coexisting isoprene efficiently increases NO x cycles during DMS photooxidation and also increases the reaction of DMS with O( 3 P) ( Reaction No. 61 in Table A4 2), producing a CH 3 SO radical with a unity yield. The resul t ing CH 3 SO is efficiently oxidized into a CH 3 (O)S(O) radical that is known to be a critical intermediate for the formation of SO 2 and MSA (Yin et al., 1990b) The effect of isoprene on MSA production is complicated because is oprene influences both gas phase reactions and heterogeneous reactions. Similarly to H 2 SO 4 MSA form a tion in the gas phase is increased with higher isoprene conc en trations due to the higher production of the CH 3 (O)S(O) radical The MSA and H 2 SO 4 produce d in the gas phase reaction s y n ergetically increase the pathway to the MSA formation in the aerosol th r ough heterog e neous reactions of DMS oxidation pr oduc t s. Although the new ly built DMS kinetic model of this study successfully predicts the trend (Table 4 3) in the yields of MSA and H 2 SO 4 under different initial isoprene concentration s s predictions somewhat deviate from experimental data when the isoprene concentration is high. Similarly, for Exp iso DMS 1 3 i n F igure 4 4 the model underpre dicts MSA concentrations. T he gap between measurement and prediction increases as the initial isoprene concentration increases. It is expected that the secondary organic aerosol (SOA) formed from isoprene photooxidation would influence the formation of M SA, possibly because the SOA might increase the solubility

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78 of DMS products such as DMSO. The heterogeneous chemistry on SOA is not included in this study and this may possibly lead to experimental data. Potent ial A pplication of the K inetic M odel in A mbient S imulation To evaluate the model performance for lower concentrations of isoprene and DMS, Exp iso DMS 4 and 5 were conducted T he simulation accords well with the measurements (Figure 4 5) for both gas pha se and aerosol phase products suggesting that the new ly constructed DMS kinetic model could potentially be suitable for ambient simulation. Conclusion and Atmospheric Implication In this study, the modeling of DMS oxidation mechanism s has been advanced by including both the most recent reaction rate constants and heterogeneous reactions of gas phase DMS oxidation products in the aerosol The newly constructed kinetic model closely matches the experimental data for the DMS decay and time profiles of NO x O 3 SO 2 and DMSO 2 The prediction of H 2 SO 4 and MSA concentrations has been significantly improved by the model of this study as compared with model s that neglect heterogeneous reactions of gaseous DMS oxidation products. The MSA production appeared to be increase d as the initial isoprene concentration increase d The IRR analysis in the model suggests that the presence of isoprene increases NO x cycles during the DMS photooxidation Subsequently, the reaction of DMS with O( 3 P) is enhanced, eventually caus ing higher yields of MSA and H 2 SO 4 through gas phase reactions. With greater production of MSA and H 2 SO 4 in the presence of high concentration s of isoprene, the heterogeneous reactions of DMSO and MSIA were also enhanced in turn produc ing more MSA. T he formation of isoprene SOA

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79 may also increase the yields of MSA and H 2 SO 4 through some unknown mechanism s via heterogeneous reactions of DMS oxidation products To apply the model to the reaction in ambient air further investigation is needed not only to u nderstand the detailed mechanism s of aerosol formation from DMS oxidation in the presence of SOA but also to improve the model for SOA production in the presence of DMS In addition, Zhu et al (2006) indicated t hat the OH radical reaction with MSA consumes almost 20% of MSA and produces about 8% of H 2 SO 4 within 3 days under typical marine atmospheric conditions. In this study, due to the short duration (~3 hours), the MSA decay might be in significant. However this should be considered when the model is applied to the reactions in the ambient air Similar to the MSA production th r ough heterogeneous reactions of DMSO, SO 2 can be oxidized on the surface of aerosol but will not be significant because of its low reactivity with oxidants (e.g., OH radical). However, in the ambient air the heterogeneous production of H 2 SO 4 through SO 2 reactions on aerosol should be conside rable especially in the presence of atmospheric catalysts such as iron ions (Freiberg, 1974)

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80 Table 4 1 Chamber experiments of the ph otooxidation of DMS and DMSO in the presence of NO x Exp Temp RH % In i tial sulfur conc., ppb In i tial NO x conc., ppb DMSO 1 22 24 291 49.1 DMSO 2 22 26 306 199.1 DMSO 3 21 23 99 33.0 DMSO 4 24 24 170 85.1 DMSO 5 26 27 7 6 33.0 DMS 1 24 28 714 103.7 DMS 2 26 28 210 203.3 DMS 3 25 2 8 146 26. 4 DMS 4 27 4 0 134 21.7 DMS 5 25 60 161 81.0

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81 T able 4 2 Chamber e xperiment al conditions for isoprene photooxidation with and without DMS Exp Temp o C RH % Initial DMS conc., ppb Initial isoprene conc., ppb Initial NO x conc., ppb iso 1 24.5 30 0 644 76.9 iso 2 25.0 32 0 600 26.7 iso DMS 1 23.5 28 243 560 84.8 iso DMS 2 23.2 30 265 1360 84.5 iso DMS 3 23.0 30 276 22 50 65.9 iso DMS 4 22.0 10 31 210 40.3 iso DMS 5 2 3 1 3 0 20 40 15.6 Initial DMS and isoprene concentration s in iso DMS 5 were estimated based on the amount of injected chemicals due to the instrumental detection limit

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82 Table 4 3 Model simulation of the yields of MSA and H 2 S O 4 and the integrating reaction rate s (IRR) of the formation of MSA and H 2 SO 4 in the presence of d ifferent amount of isoprene. a. Exp isoprene conc., ppb Simulation time b min DMS, ppb Molar yield c. IRR normalized by DMS d. MSA formation H 2 SO 4 formation MSA H 2 SO 4 gas pathway e. aerosol pathway f. gas pathway e. aerosol pathway iso DMS 1 560 44 6.4 9.7% (8. 1 %) 0. 9 % (1.9 %) 0.092 0.001 0.008 0 iso DMS 2 1360 50 5. 9 11.0% (9.8 %) 1.0% (2.0 %) 0.108 0.002 0.010 0 iso DMS 3 2248 163 6 .0 11. 4 % (20. 8 %) 1.5% (2.3 %) 0.11 0 0.015 0.015 0 a. All the reported results (except those in brackets) in this table were based on the model simulation. The experimental yield data are in the brackets. The MSA yields in this table were calculated using the data from Figure 4 4 with corrections for DMS wall loss and chamber dilution. Note that DMS decay in Figure 4 4 contains the decay due to photooxidation, wall loss and chamber di lution. b. The simulation time was set so that the consumed DMS was fixed at around 6 ppb for fair comparison among different systems. c. Molar yield is defined as the amount of MSA (or H 2 SO 4 ) formed divided by the amount (around 6 ppb) of DMS consumed. d. Refer to 3.3.1 for the description of IRR. e. The IRR for Reaction No. 48 and 54 in Table S1 and Reaction No.132 in Table S2 were added up for MSA formation while the IRR for Reaction No. 170 and 171 in Table 3 were added up for H 2 SO 4 formation. f. The IRR for MSA formation was based on Reaction (9) in section 3.1.2 and that for H 2 SO 4 formation was from Reaction (10) in the same section.

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83 Figure 4 1 The time profiles of DMSO, DMSO 2 SO 2 NO x and O 3 for the photooxidation of DMSO in the presenc e of NO x (Exp DMSO 1 and DMSO 2 in Table 4 1). chemical s pecies and model.

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84 F igure 4 2 Model simulation of MSA and sulfuric acid for the photooxidation of DMSO in the presence of NO x (Exp DMSO 1 and DMSO 2 in Table 4 1) with (SH) and without (SN) including heterogeneous reactions. The experimentally observed concentrations (E) of MSA and H 2 SO 4 are shown as comparison.

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85 Figure 4 3 The time profiles of DMS, DMSO 2 SO 2 MSA, sulfuric acid, NO x and O 3 f or the photooxidation of DMSO in the presence of NO x (Exp DMS 3 5 in Table 4 1). chemical s model.

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86 F igure 4 4 The time profiles of isoprene, DMS, MSA and sulfuric acid for the photooxidation of DMS and NOx in the presence of 560 ppb (Exp iso DMS 1), 1360 ppb (Exp iso DMS 2), and 2248 ppb (Exp iso DMS denotes the experimentally observ ed concentrations of chemical species and The decay of DMS and isoprene w ere not co rr ected for wall loss and chamber dilution while the production of MSA and sulfuric acid was co rr ected for both the wall lo ss and chamber dilution.

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87 Figure 4 5 The time profiles of Exp iso DMS 4 (isoprene, DMS, NO x and O 3 from the photooxidation of 31 ppb of DMS and 40 ppb of NO x in the presence of 210 ppb of isoprene) and time profiles for Exp iso DMS 5 (NO x O 3 MSA and H 2 SO 4 from 20 ppb of DMS and 15 ppb of NO x in the presence of 40 ppb of isoprene). chemical s model

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88 CHAPTER 5 DOES DIMETHYL SULFIDE AFFECT SECONDA RY ORGANIC AEROSOL PRODUCTION IN AMBIENT PM 2.5 ? Background In this study, it is hypothesized that DMS can significantly increase the SOA production in ambient PM 2.5 through producing acids such as sulfuric acid and MSA, and this process may be important i n some areas. To test this hypothesis, two things were evaluated: 1) the correlations of mass of 2 methyltetrol, a marker compound of isoprene SOA (Claeys et al., 2004) as well as the mass of secondary organic car bon in ambient PM 2.5 with methanesulfonate (MS) and non seasalt sulfate (nss SO 4 2 ) in the aerosol. 2) the contributions of DMS photooxidation toward the total nss SO 4 2 which were estimated in different areas as indications of the relative importance of DMS in producing acids compared to the anthropogenic SO 2 DMS has been known to be produced from two sources: 1) the algal derived compound dimethylsulfoniopropionate in surface ocean waters and salt marshes (Dacey et al., 1987) and 2) thiols in anaerobic sediments (Finster et al., 1990) and in a variety of oxic freshwater wetland s (Drotar et al., 1987) Therefore, Cedar Key, FL, was chosen as a site representing ocean and salt marsh areas; Paynes Prairie in Micanopy, FL, was ch osen as a site representing freshwater wetland areas; and Gainesville, FL, was chosen as a site representing areas with human activities. Experimental section Sampling S ites The three sampling sites are marked in Figure 5 1. The Gainesville site ( 29.64177 82.347996 ) is on the backside of Black Hall at University of Florida.

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89 The Paynes Prairie site ( 29.541418 82.290764 ) is located beside the EPA sampling site in Paynes Prairie State Park ( AIRS ID # B001 3011 ). The Cedar Key site ( 29.151444 83.049217 ) is located at a private dock near the sea. Sampling and S ample P reparation Aerosol samples were mainly taken in summer 2011 and spring 2012 in the abovementioned three sites in Florida. For each sampling day, aerosol samples (PM 2.5 ) were taken for 3 hours both in the morning (9:30 am to 12:30 pm) and in the afternoon (13:00~16:00). The air was samp led at a height of around 2 meters above ground under ambient conditions at a flow rate of ~1.2 m 3 min 1 The aerosol samples were collected on pre baked quartz microfiber filters (20.3 25.4 cm, Whatman, England). Each filter was kept in a pre cleaned la rge glass jar and the glass jars were kept inside a cooler filled with ice. The sample restoration time was shorter than 6 hours. After sampling, each quartz filter was cut into two equal pieces. O ne piece was dissolved in ~30 m L of acetonitrile (optima grade, Fisher Scientific) with Bornyl Acetate as internal standard. After three 30 minute sonification, the solution was filtered using Acrodisc 13 mm Syringe Filter with 0.45 m nylon membrane (PALL). 8 m L of the filtered solution was transferred to a t ube together with 150 L of O (2,3,4,5,6 Pentafluorobenzyl) hydroxylamine hydrochloride ( PFBHA ) derivatization reagent The remaining solu tion was concentrated to ~1.5 m L using a Rotary Evaporator (Heidolph Laboratory 4001) and transferred to a small via l with 50 l of N,O bis(trimethylsilyl) trifluoroacetamide (BSTFA) derivatization reagent Further

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90 descriptions of sample extraction procedures and derivatization methods for carbonyls ( PFBHA ) and for alc o hols ( BSTFA) can be found elsewhere (Jang and Kamens, 1999) Another piece of the quartz filter was punched using two punchers: a 0.625 inch puncher for organic carbon (OC) analysis and a 1.25 inch puncher for inorganic ion analyses. Analytical M ethods Organic C ompounds A nalyses All the treated samples were analyzed by a ga s chromatograph ion trap mass spectrome ter ( GC ITMS Varian model CP 3800 GC, Saturn model 2200 MS) with a 30m capillary column ( ID=0.25mm, Varian, Factor Four VF 5ms CP8944 ) using the temperature program as follows: 80 o C for 1 min; ramp to 100 at 5 o C min 1 ; hold for 3 min; ramp to 280 o C at 10 o C min 1 and hold for 8 min. F our levels of external standard solutions containing six different carbonyl compounds (trans 2 hexenal, acrolein, methacrolein trans 2 methyl 2 butenal glyoxal and methylglyoxal) and o ne alcohol compound (butane 1,2,3,4 tetrol) in acetonitrile were used for calibration The detailed calibration procedures can be found in the previous study (Im et al., 2011) The mass spectra of the target comp ounds are summarized in Table B 1. The average errors associated with concentrations of organics are 20%. Organic C arbon A nalysis The quartz filter ( 0.625 inch in diameter) punched from the large quartz was placed into an organic carbon/ elemental carbon a nalyzer (OC/EC, Sunset Laboratory Model 4) and the analysis was run using the NIOSH 5040 method.

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91 Secondary organic carbon (OC sec ) concentration was calcu lated using the measured elementary carbon (EC) concentration multiplied by the p rimary organic carbon (O C pri )/ EC ratio (shown in Figure B 1 ) with an estimated error of 1 4 % The OC sec calculation technique has been described in the previous study (Cabada et al., 2004) I norganic I on A nalyses A n ion chromatograph (Metrohm, 761 Compact IC) was used to measure the major aerosol components The el u ent flow rate was 0.7 mL min 1 in the anion column and 0.9 mL min 1 in the cation column. The cation eluent was 2.0 mM HNO 3 a nd the anion eluent was 9.57 mM Na 2 CO 3 + 2.4 mM NaHCO 3 The IC column used for cations and anions were Metrosep C 4 100 and IonPac AS9 HC, respectively The detection limit of PILS IC is 0. 01 g m 3 and the associated error is 10%. Seasalt sulfate (ss SO 4 2 ) concentration was calculated using the measured Na + concentration with the generally accepted ss SO 4 /Na + molar ratio (0.06) (Lide, 1999) T he concentration of non seasalt sulfate (nss SO 4 2 ) was calculated by subtracting the total sulfate ( SO 4 2 T ) c oncentration by the ss SO 4 2 concentration Results and Discussion Correlation of the A cids (NO 3 nss SO 4 2 and MS ) a nd O rganics (2 methyltetrol and OC sec ) Winter In winter the flux of both DMS and isoprene are low (Korhonen et al., 2008; Wang and Shallcross, 2000) To confirm the low MSA and isoprene SOA in winter time, two s amples were collected in Gainesville on 12/2/2012 (Table 5 1). The resulting data shows that 2 methyltetrol (P 1 ) OC sec MS and SO 4 2 are low.

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92 Interestingly, carbonyls such as methacrolein (P 2 ), methyl vinyl ketone (P 3 ), glyoxal (P 4 ) and methylglyoxal (P 5 ) are relatively high in concentration. Possible explanations for that are 1) the stronger condensation in lower temperature and 2) the slower gas phase decay under weaker sunlight. The major source of SO 4 2 in aerosol may be from anthropogenic SO 2 so th e DMS effect on SOA formation is unclear. Hence, winter is not within the interest of this study. S pring and summer 2 methyltetrol is an important fingerprint of the SOA formed from isoprene (2004) and has been found to have higher concentration during sp ring a nd summer compared with winter (Xia and Hopke, 2006) In this study, to better show the acidity effect of H 2 SO 4 and MSA on ambi ent SOA, ambient PM 2.5 were collected mainly during spring and summer. Figure 5 2 A shows a strong correlation (R 2 =0.85) between 2 methyltetrol ( ) and acids [methanesulfonate ( ) and non seasalt sulfate ( )] in ambient PM 2.5 ( 5 1 ) Table 2 summarizes all the P values for NO 3 nss SO 4 2 and MS in three sampling sites Due to its high P value ( > 0.17) in all sites, nitrate s are not included i n Eq. 5 1 The P value s of nss SO 4 2 and MS are very low in Paynes Prairie and Gainesville, which indicates strong acid catalyzed heterogeneous reactions of epoxides on the surface of acidic aerosol as proposed by other researchers (Surratt et al., 2010; Lin et al., 2012) Interestingly, the P value of neither nss SO 4 2 nor MS in Cedar Key is low. A possible reason is the low concentration of 2 methyltetrol

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93 detected in the coastal area suc h as Cedar Key as supported by the other study (Xia and Hopke, 2006) Another possible reason is that 2 methyltetrol in coastal air may be stro ngly influenced by isoprene flux from the ocean phytoplankton activities while 2 methyltetrol in terrestrial air is from isoprene emitted by trees in a relatively stable flux. OC sec is a more direct representative of SOA and thus it is also used to correla te with the acids in ambient aerosol. P values for NO 3 are still high in all the sites (Table 2) so again NO 3 is not included in the regression. The P values for nss SO 4 2 and MS are generally low. Figure 5 2 B shows a strong correlation (R 2 =0.85) bet ween OC sec and acids ( and ). ( 5 2 ) Given the fact that 2 methyltetrol contributes only a small mass fraction of OC sec the strong correlation between OC sec and acids suggest s that there are considerable amounts of other compounds (e.g., carbonyls) in the aerosol that are sensitive to the acidity. The concentrations of several carbonyl compounds (P 2 P 5 ) are illustrated in Figure 5 3 together with those of 2 methyltetrol. The carbonyls generally show a similar tendency with 2 methyltetrol suggesting the good correlations of these carbonyls with the aerosol acidity comp osed of MS and SO 4 2 Source of MSA MSA has been shown to be important for SOA mass increase in this study. Generally speaking, MSA is thought to be the product of DMS which is emitted from ocean. However, both Gainesville and Paynes Prairie areas show stronger effect of

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94 MSA on the SOA mass production than Cedar Key. To understand the reason behind it, the fi rst question to answer is whether MSA concentrations in aerosol increase in terrestrial areas compared with those in coastal areas. The MS / ss S O 4 2 values were used as an indication of MSA formation in the aerosol due to the photooxidation of DMS in terr estrial areas since ss S O 4 concentration is only subject to the physical processes. Table 5 3 lists the MS / ss S O 4 2 values for all the samples. On average, Cedar Key has the smallest MS / ss S O 4 2 value (0.16); Gainesville has the medium value (0.45); an d Paynes Prairie has the highest value (0.67). Although Cedar Key may have sufficient DMS from ocean, due to the trivial traffic, anthropogenic NO x is small so the MSA formation is reduced (Barnes et al., 1988) The reason why Paynes Prairie area has a considerable amount of MSA formation is probably due to the additional DMS flux from the oxic freshwater wetl and microorganisms plus a reasonable amount of NO x from the adjacent traffic on US 441 It is beyond the scope of this study to discuss the mechanism of DMS production from different types of wetland, but it is clear that oxic freshwater wetland tend to p roduce more DMS in north central Florida. As shown in Figure 5 1, wetlands are ubiquitous in Florida, thus providing a huge source for MSA in this area. The C ontribution of n ss S O 4 ( DMS S O 4 2 ) from DMS P hotooxidation to the T otal S O 4 2 (SO 4 2 T ) MSA is almost exclusively from DMS photooxidation (Watts et al., 1987; Legrand and Saigne, 1988) so DMS effect on SOA production through the formation of MSA is clear. However, there are two sources of n ss S O 4 2 : 1) DM S photooxidation ( DMS S O 4 2 ) and 2) anthropogenic SO 2 photooxidation ( SO 2 n ss

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95 S O 4 2 ) In order to understand the impact of DMS on SOA mass increase, the contribution of sulfate in aerosol by DMS photooxidation in different sites need to be estimated. An i soprene/NO x /DMS photochemical reaction mechanism has been proposed by Chen and Jang (2012b) T he model can predict the MSA and H 2 SO 4 formation fro m DMS photooxidation. Simulations have been done using the real sun light spectrum of a typical sunny day and the mechanism developed in the chamber work to predict the MS /DMS S O 4 2 ratio in the morning (around 10:30) and afternoon (around 15:00). The emission rate constant of isoprene ( molecules cm 3 s 1 ) and DMS ( molecules cm 3 s 1 ) were obtained from the estimation by Williams et al. (2001) in their ambient modeling study. The concent ration of NO was assumed to be introduced to the system in the early morning (5:00) with no further NO flux during the day. A system dilution factor was predetermined to balance the incoming DMS flux. It was found through model simulation that the MS /DM S S O 4 2 ratio is not sensitive to the initial concentration of either isoprene or DMS within at least one order of magnitude. Figure 5 4 shows the relation of MS /DMS S O 4 2 ratio with two critical factors: initial DMS concentration and initial NO conc entration. The ranges of the initial concentrations of DMS and NO in different sites both in the morning and afternoon are given in Table A 2 together with the ranges of the corresponding MS /DMS_ S O 4 2 ratio. The DMS_ S O 4 2 values were calculated using the measured MSA concentration and the MS /DMS S O 4 2 ratio. Table 5 3 summarizes the contribution

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96 of DMS S O 4 2 to S O 4 2 T in different sites. All of the sites show large deviation of contribution of DMS S O 4 2 to S O 4 2 T In Cedar Key, no apparent rel ation was found between the wind direction and the contribution of DMS_ S O 4 2 over SO 2 S O 4 2 to S O 4 2 T This can possibly be explained by the different ocean plankton activities that emit DMS. Paynes Prairie is influenced more by the an thropogenic SO 2 bu t due to the high DMS flux from the freshwater wetland, DMS_ S O 4 2 is still a major fraction of S O 4 2 T. Table 5 3 shows that when the dominating wind direction is north, DMS S O 4 2 / S O 4 2 T ratio is significantly high than when the dominating wind directi on is south (the p value for the null hypothesis that DMS S O 4 2 / S O 4 2 T ratio is same for north wind and south wind is 0.1 6 ). This suggests that the anthropogenic NO x from Gainesville increases the decay of DMS forming more sulfates. Similarly, Table 5 3 also shows that in Gainesville, when the dominating wind direction is north, DMS S O 4 2 / S O 4 2 T ratio is significantly lower than when the dominating wind direction is south (the p value for the null hypothesis that DMS S O 4 2 / S O 4 2 T ratio is same for north wind and south wind is 0. 08 ). Deerhaven Generating Station with coal power plant, one of the major coal power plants in Florida is in the north of Gainesville. Therefore, the high DMS S O 4 2 / S O 4 2 T ratios with north wind suggest that an impo rtant source of anthropogenic SO 2 S O 4 2 may be from the Deerhaven Generating Station In general, DMS_ SO 4 2 should not be ignored in all the sites of our study.

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97 Conclusions and Atmospheric Implications Air pollution issues should be addressed both in regi onal scales and global scales. Although globally SO 2 flux is much higher than DMS, this might not be t he case in regional scales For example, both the high DMS_ S O 4 2 DMS / S O 4 2 T ratios and the MS / ss S O 4 2 ratios in Paynes Prairie suggest possible DMS s ource from the prairie area. Thus, DMS photooxidation in coastal areas and wetland areas can be an important source of acid that increases SOA formation in ambient PM 2.5 Florida has potential source of DMS since it is surrounded by ocean and filled with numerous wetlands. Meanwhile, isoprene flux in Florida can be high due to the abundance of oak trees. With relatively little industrial emission but abundant flux of isoprene and DMS, the DMS impact on SOA mass should be considered in regional air qualit y modeling of this area Besides Florida, Amazon rain forest may also be an interesting spot to study the contribution of DMS on isoprene SOA owing to the high emission of different types of volatile organic compounds including isoprene (Guenther et al., 1995; Kesselmeier et al., 2000) and DMS (Andreae and Andreae, 1988; Andreae et al., 1990) 2 methyltetrols were first detected in the aerosol sampled from Amazon rain fore st by Clayes et al. (2004) as isoprene SOA marker compounds and the formation of 2 methyltetrols was later confirmed to be highly dependent on the aerosol acidity (Edney et al., 2005; Jaoui et al., 2008; Surratt et al., 2007b) However, the source of the acidic aerosol in the Amazon rain forest has not yet been studied and it is probably from the photooxidation of DMS. Therefore, contrary to the widespread assumption that SO 2 is the predominant global source of

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98 acid, our study suggest the importance of DMS in producing acidic aerosol that can enhance the SOA formation in certain regional areas.

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99 Table 5 1 The concentrations of the organic and inorganic compounds in the a mbient aerosol sampled in different sites a Location Date Time No. Major organics Major inorganics SOC P 0 P 1 P 2 P 3 10 P 4 10 MS SO 4 NO 3 Cl Na + NH 4 + Gainesville 6/14/2011 morning 1 7.27 0.12 0.22 0.29 0.08 0.46 0.19 6.70 1.17 1.06 6.43 0.4 5 afternoon 2 7.49 0.12 0.25 0.32 0.10 0.82 0.17 6.30 0.67 0.54 4.89 0.32 9/8/2011 morning 3 3.43 0.08 0.13 0.16 0.02 0.16 0.15 1.80 0.58 1.79 2.22 0.55 afternoon 4 3.23 0.06 0.05 0.07 0.01 0.07 0.12 1.31 0.28 1.23 1.73 0.47 9/14/2011 morning 5 8.22 0.14 0.10 0.13 0.03 0.11 0.17 6.10 0.26 1.28 2.12 0.57 afternoon 6 8.58 0.09 0.16 0.20 0.03 0.14 0.07 6.89 0.27 0.29 1.75 0.64 4/17/2012 morning 7 3.09 0.01 0.08 0.08 0.01 0.23 0.0 3 1.51 0.12 0.18 0.70 0.12 afternoon 8 3.99 0.15 0.10 0.12 0.07 0.53 0.28 1.68 0.32 0.13 0.81 0.11 4/25/2012 morning 9 4.75 0.07 0.04 0.08 0.05 0.23 0.14 2.22 0.52 0.89 1.11 0.92 afternoon 10 5.37 0.14 0.10 0.18 0. 06 0.47 0.20 3.24 0.72 0.68 1.22 0.67 12/2/2012 morning 11 1.95 0.00 0.33 0.26 0.31 0.62 0.01 1.15 0.09 0.39 0.28 0.44 afternoon 12 2.11 0.01 0.30 0.17 0.24 0.56 0.01 1.16 0.27 0.55 0.35 0.59 Cedar Key 6/22/2011 mornin g 13 2.92 0.02 0.10 0.13 0.01 0.27 0.08 1.89 3.02 2.11 2.67 1.07 afternoon 14 3.05 0.03 0.12 0.15 0.04 0.44 0.10 2.00 2.20 1.78 2.56 1.34 3/14/2012 morning 15 2.96 0.01 0.09 0.09 0.01 0.09 0.02 1.32 0.51 0.63 0.45 1. 07 afternoon 16 3.12 0.02 0.03 0.03 0.01 0.05 0.03 1.72 0.40 0.58 0.59 0.86 4/4/2012 morning 17 2.10 0.00 0.01 0.02 0.01 0.10 0.02 0.57 0.21 0.39 0.59 0.36 afternoon 18 2.59 0.00 0.01 0.02 0.00 0.04 0.03 0.88 0.31 0.22 0.80 0.22 Paynes Prairie 9/30/2011 morning 19 5.89 0.09 0.23 0.29 0.20 1.03 0.18 2.05 0.56 0.51 1.12 0.65 afternoon 20 4.92 0.05 0.27 0.35 0.10 0.71 0.14 1.56 0.86 0.10 0.32 0.80 3/21/2012 morning 21 2.86 0.02 0.07 0.08 0.01 0.09 0.06 1.08 0.56 1.03 0.68 0.62 afternoon 22 2.74 0.03 0.09 0.09 0.02 0.17 0.10 1.26 0.63 0.69 0.55 0.66 3/28/2012 morning 23 3.34 0.03 0.04 0.05 0.02 0.14 0.04 1.89 0.21 0.08 0.52 0.43 afternoon 24 2.9 0 0.04 0.05 0.07 0.03 0.21 0.03 2.10 0.37 0.07 0.57 0.31 a. See section 2.3.1, 2.3.2 and 2.3.3 for the associated errors

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100 Table 5 2 P values of the concentrations of NO 3 MS and nss SO 4 2 for the prediction of the concentrations of 2 methylt etrol and secondary organic carbon (OC sec ) using a multiple linear regression. Location 2 methyltetrol OC sec NO 3 MS nss SO 4 2 NO 3 MS n ss SO 4 2 Gainesville 0.30 0.00 0.00 0.35 0.01 0.00 Cedar Key 0.74 0.21 0.24 0.74 0.42 0.05 Paynes Pra irie 0.17 0.02 0.05 0.35 0.04 0.05

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101 Table 5 3 The summary for the MS /ss SO 4 2 ratio, the c ontribution of SO 2 to SO 4 2 T the c ontribution of DMS to SO 4 2 T and wind direction for each sample a. The wind direction was obtained from http://weather.org/weatherorg_records_and_averages.htm Location Date Time MS / ss S O 4 2 Contribution of SO 2 to SO 4 2 T Contribution of DMS to SO 4 2 T wind direction a Gainesville 6/14 morning 0.12 62% 14% NW afternoon 0.14 57% 24% NW 9/8 morning 0.27 29% 40% W afternoon 0.27 9% 57% W 9/14 morning 0.32 78% 14% NE afternoon 0.16 85% 9% NE 4/ 17 morning 0.31 83% 10% E afternoon 1.79 10% 83% SE 4/25 morning 0.50 57% 30% W afternoon 0.65 38% 53% SW Cedar Key 6/22 morning 0.12 19% 45% Weak afternoon 0.15 14% 54% SW 3/14 morning 0.21 76% 16% Weak afternoon 0.21 59% 32% Irr egular 4/4 morning 0.11 44% 30% SW afternoon 0.13 24% 54% W Paynes Prairie 9/30 morning 0.64 18% 68% NW afternoon 1.78 5% 90% NW 3/21 morning 0.32 45% 39% SE afternoon 0.70 18% 71% SE 3/28 morning 0.31 76% 17% SE afternoon 0.24 71% 22% SE

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102 Figure 5 1 Geographical location of the sampling sites and distribution of different types of wetland near sampling sites.

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103 Figure 5 2 The predicted concentrations of 2 methyltetrol ( OCsec ) vs. the measured concentrations ( A) 2 methyltetrol ( B) secondary organic carbon (OC sec )

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104 Figure 5 3 C oncentration of different organic compounds in the ambient PM 2.5 collected at three different locations in different days. The sample identification number (ID) is shown in Table 5 1. The average errors associated with concentrations of organics are 20%.

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105 Figure 5 4 Model predictions of MS / DMS_ SO 4 2 at 10:30 EST (A) and 15:00 EST (B) using the sunlight spectrum of a typical sunny day with different initial concentrations of DMS and NO in the early morning assuming a constant flux of DMS during the day.

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106 CHAPTER 6 CONCLUSIONS A detailed knowledge of the atmospheric interaction of DMS and isoprene through photochemical reactions is necessary to accurately model the SOA formation in ambient air. The aims of this work were therefore to : 1) investigate and confirm the effect of DMS on the increase of isoprene SOA yield; 2) demons trate the acid catalyst function of MSA on the isoprene SOA formation; 3) p redict the acidic aerosol formation through DMS photooxidation using a kinetic model; and 4) f ind evidences of DMS impact s on SOA mass increase in ambient air. I ndoor chamber expe riments in combination with o rganic c arbon analy tical techniques were used to estimate the isoprene SOA yield ( Y iso ) in the DMS/isoprene/NO x system We found that, under our specific experimental conditions, t he Y iso is increased by 30% to 1 50 % due to th e presence of DMS Our study suggests that the heterogeneous reactions of isoprene oxidation products with the highly acidic products (e.g., MSA and sulfuric acid ) from DMS photooxidation can considerably contribute to the Y iso increase. By comparing the Y iso after nebulization of H 2 SO 4 and MSA, o ur study showed that MSA aerosol can significantly increase the isoprene SOA yield similarly to H 2 SO 4 The yields of 2 methyltetrol and several c arbonyl products in isoprene SOA also appeared to be statistically h igher with MSA aerosol compared to those without MSA The results from the product analysis from the chamber study suggest MSA accelerates the aerosol phase heterogeneous reactions of epoxides and carbonyl products increasing SOA yields.

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107 The prediction mo del of DMS photooxidation included in this study predicted that concentrations of both MSA and H 2 SO 4 would significantly increase due to heterogeneous chemistry, and this was well substantiated with experimental data. The model used in this study also pre dict ed the decay of DMS, the formation of other gaseous products such as SO 2 dimethyl sulfone (DMSO 2 ), and the ozone formation linked to NO x cycle Th e strong correlation between organics and two acids (H 2 SO 4 and MSA) in ambient PM 2.5 co ll ected at three di fferent sampling sites suggest s that MSA significantly influences on ambient SOA formation through aerosol phase reactions of the organic compounds. The s ignificant contribution s (9%~90%) of the sulfate from DMS to the total sulfate were observed in all t he sampling sites This study suggests that DMS is a significant source of acidic aerosol (H 2 SO 4 and MSA) that increases SOA production in the coastal area and in the land surrounded by fresh water wetland or salt marsh.

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108 CHAPTER 7 FUTURE STUDIES The curr ent research bridges the study of DMS chemistry and the study of SOA formation, suggesting the potentially interesting atmospheric chemistry in the aerosol formation in the areas where both isoprene flux and DMS flux are high. In the future, there are sev eral directions for further study of the DMS effect on SOA formation. 1. The relative effect of MSA on SOA mass production compared to H 2 SO 4 More extensive studies are needed for understanding the MSA effect on different types of SOA formation (e.g., pinene, limonene) as compared to H 2 SO 4 effect. This will benefit the modeling of ambient SOA in the presence of MSA and H 2 SO 4 2. Marker compounds of heterogeneous reactions of MSA and isoprene products No marker compounds (presumably organosulfonates) of heterogeneous reactions of MSA and isoprene products have been detected either in chamber study or in ambient aerosol. LC/MS/MS analysis is necessary in the future to prove the existence of the marker compounds. 3. More ambient samples in wetland areas and rain forest areas. Due to the limitation of the current study, only a few samples were obtained in three sampling sites. In the future, if possible, more ambient samples should be collected and analyzed especially in wetland areas and rain forest areas to see how important DMS (or probably some other reduced sulfur like H 2 S) is in increasing the regional SOA production by nature.

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109 4. Better SOA sub model for air quality model As a further step of this research, the prediction of SOA from chamber study of the D MS/isoprene/NO x system needs to be achieved. In addition to the SOA model that considers acid catalyzed heterogeneous reactions of organics, a DMS photooxidation model that includes the SOA effect on the formation of MSA and H 2 SO 4 on aerosol surface shoul d be developed. In the long run, a ir quality model in the future should consider including the suggested chemistry in this study to better predict the ambient SOA mass.

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110 APPENDIX A SUPPLEME N TARY MATERIALS FOR CHAPTER 4 The artifacts of DMSO measurement in the presence of DMS The prediction of DMSO (not shown in the figures) is systematically much lower than the measured DMSO. However, as explained by Sorensen et al (1996) the fast reaction b etween DMSO and OH sh ould lead to the scavenging of the DMSO formed so the detected DMSO should be little It is thus possible that the measurement of DMSO rather than the model prediction is problematic. It has been reported by Gershenzon (2001) that DMS and O 3 can rapidly react in the water with a reaction rate constant of ~10 9 M 1 s 1 at room temperature, forming DMSO with a nearly unity yield. In contrast, the liquid phase reaction between DMSO and O 3 was found to be ~10 8 times slower than that between DMS and O 3 so once DMSO is formed as a product of D MS and O 3 reaction, it will not be rapidly consumed by O 3 It is thus reasonable to assume that the high concentration of DMSO measured in the presence of DMS was an artifact due to the liquid phase reaction of DMS and O 3 collected in the liquid N 2 trap ( ~ 195 o C while the melting point of DMS is 98 o C and that of O 3 is 192 o C). Rapid liquid phase reaction of DMS and O 3 is most likely to occur when the cold trap is heated. In order to prove this hypothesis, 600 ppb DMS and 200 ppb O 3 were injected into the chamber, then the chamber air was sampled using the liquid N 2 trap. Since the rate of the reaction of DMS with O 3 in gas phase is known to be in the order of 10 20 cm 3 molecules 1 s 1 there should be theoretically no or little DMSO detected. Nevert heless, with 10 ppb of DMS decay, 180 ppb of DMSO

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111 was detected, which demonstrated that the DMSO sampling method causes a significant amount of artifacts. As a result, measured DMSO concentrations in the experiments containing DMS were not used in this st udy.

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112 Table A 1 DMSO photooxidation mechanisms DMSO Reactions Rate constant Note Initial reactions 1 CH 3 S(O)CH 3 + O 3 2 + CH 3 + CH 3 2.0E 12exp(440/T) (Sander, 200 6) 2 CH 3 S(O)CH 3 + OH 3 S(OH)(O)CH 3 6.1E 12exp(800/T) (Sander, 2006) 3 CH 3 S(O)CH 3 + NO 3 2 + CH 3 (O)S(O)CH 3 2.90E 13 (Sander, 2006) 4 CH 3 S(O)CH 3 + NO 2 CH 3 (O) S(O)CH 3 + NO 0 Primary products a. CH 3 r eactions (see CH 4 reactions) b. CH 3 S(OH)(O)CH 3 reactions 5 CH 3 S(OH)(O)CH 3 3 S(O)OH+ CH 3 1.50E+07 (Veltwisch et al., 1980) 6 CH 3 S(OH)(O)CH 3 + O 2 3 (O)S(O)CH 3 + HO 2 1.20E 12 c. CH 3 (O)S(O)CH 3 and its further reactions 7 CH 3 (O)S(O)CH 3 3 (O)S(O)CH 2 .+ H 2 O 1 .00E 14 (Yin et al., 1990b) 8 CH 3 (O)S(O)CH 2 + O 2 3 (O)S(O)CH 2 OO 7.30E 13 (Yin et al., 1990b) Secondary Products b. CH 3 (O)S(O)CH 2 OO reactions 9 CH 3 (O)S(O)CH 2 OO 3 (O)S(O)CH 2 O + NO 2 5.00E 12 (Yin et al., 1990 b) 1 0 CH 3 (O)S(O)CH 2 OO + CH 3 S 3 (O)S(O)CH 2 O + CH 3 SO 5.00E 11 (Kukui et al., 2003) 11 CH 3 (O)S(O)CH 2 OO + CH 3 SO 3 (O)S(O)CH 2 O + CH 3 (O)S(O) 4.00E 12 (Yin et al., 1990b) 12 CH 3 (O)S(O)CH 2 OO + CH 3 (O)S(O) 3 (O)S(O)CH 2 O + CH 3 SO 3 2 .50E 13 (Yin et al., 1990b) 13 CH 3 (O)S(O)CH 2 OO + HO 2 3 (O)S(O)CH 2 OOH+ O 2 1.50E 12 (Yin et al., 1990b) 14 CH 3 (O)S(O)CH 2 OO + CH 3 O 2 3 (O)S(O)CH 2 O + O 2 + CH 3 O. 1.80E 13 (Yin et al., 1990b) 15 CH 3 (O)S(O)CH 2 OO + CH 3 (O)S(O)CH 2 OO 2CH 3 (O)S(O)CH 2 O + O 2 8.60E 14 (Yin et al., 1990b)

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113 Table A 1 Continued DMSO Reactions Rate constant Note Tertiary and further products a. CH 3 S(O)OH reactions 16 CH 3 3 (O)S(O) + H 2 O 1. 16 E 1 0 (Kukui et al., 2003) 17 CH 3 S(O)OH + CH 3 SO 3 3 (O)S(O) + CH 3 SO 3 H 2.00E 13 (Yin et al., 1990b) 18 CH 3 S(O)OH + CH 3 3 (O)S(O) + CH 3 OH 1.00E 13 (Yin et al., 1990b) 19 CH 3 S(O)OH + O 3 3 (O)S(O) + OH 1. 00E 13 (Yin et al., 1990b) 20 CH 3 S(O)OH + NO 3 3 (O)S(O) + HNO 3 1.00E 13 (Yin et al., 1990b) 21 CH 3 S(O)OH + HO 2 3 (O)S(O) + H 2 O 2 1.00E 15 (Yin et al., 1990b) 22 CH 3 S(O)OH + CH 3 O 2 3 (O)S(O) + CH 3 OOH 1.0 0E 15 (Yin et al., 1990b) b. CH 3 (O)S(O)CH 2 O reactions 23 CH 3 (O)S(O)CH 2 O 3 (O)S(O) + H CO H 1.00E+01 (Yin et al., 1990b) c. CH 3 (O)S(O). reactions 24 CH 3 (O)S(O) + NO 2 3 SO 3 + NO 5.00E 13 Estimate 25 CH 3 (O)S(O) + O 3 3 SO 3 + O 2 5.00E 15 (Yin et al., 1990b) 26 CH 3 (O)S(O) + HO 2 3 SO 3 + OH 2.50E 13 (Yin et al., 1990b) 27 CH 3 (O)S(O) 3 + SO 2 1.00E+01 (Mellouki et al., 1988) 28 CH 3 (O)S(O) + O 2 3 (O)S(O)OO 2.60E 18 (Yin et al., 1990b) 29 CH 3 ( O)S(O)OO 3 (O)S(O) + O 2 3.30 (Yin et al., 1990b) 30 CH 3 (O)S(O) + NO 3 3 SO + NO 2 1.00E 14 (Yin et al., 1990b) 31 CH 3 (O)S(O) + CH 3 O 2 3 SO 3 + CH 3 O 2.50E 13 (Yin et al., 1990b) 32 CH 3 (O)S(O) + CH 3 S 3 (O)S(O)S CH 3 4.20E 11 (Yin et al., 1990b) 33 CH 3 (O)S(O) + CH 3 (O)S(O) 3 SO + CH 3 SO 3 7.50E 12 (Yin et al., 1990b) 34 CH 3 (O)S(O) + CH 3 S NO 3 (O)S(O)CH 3 + N O 6.80E 13 (Yin et al., 1990b) 35 CH 3 (O)S(O) + OH 3 SO 3 H 5.00E 11 (Yin et al., 1990b) d. CH 3 (O)S(O)OO reactions 36 CH 3 (O)S(O)OO 3 SO 3 + NO 2 1.00E 11 (Yin et al., 1990b)

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114 Table A 1 Continued DMSO Reacti ons Rate constant Note 37 CH 3 (O)S(O)OO + NO 2 3 (O)S(O)OONO 2 1.00E 12 (Yin et al., 1990b) 38 CH 3 (O)S(O)OONO 2 3 (O)S(O)OO + NO 2 4.20E 03 (Yin et al., 1990b) 39 CH 3 (O)S(O)OO + CH 3 S 3 SO 3 + CH 3 SO 6.00E 11 (Yin et al., 1990b) 40 CH 3 (O)S(O)OO + CH 3 SO 3 SO 3 + CH 3 (O)S(O) 8.00E 12 (Yin et al., 1990b) 41 CH 3 (O)S(O)OO + CH 3 (O)S(O) 3 SO 3 3.00E 13 (Yin et al., 1990b) 42 CH 3 (O)S(O)OO + HO 2 3 (O)S(O)OOH + O 2 2.00E 12 (Yin et al., 1990b) 43 CH 3 (O)S(O)OO + CH 3 O 2 3 SO 3 .+ CH 3 O + O 2 5.50E 12 (Yin et al., 1990b) 44 CH 3 (O)S(O)OO +CH 3 (O)S(O)OO + CH 3 SO 3 SO 3 + O 2 6.00E 12 (Yin et al., 1990b) 45 CH 3 (O)S(O)OO + CH 3 S 3 (O)S(O)OOH + CH 3 SO. 4.00E 13 (Yin et al., 1990b) e. CH 3 SO 3 reactions 46 CH 3 SO 3 3 + CH 3 4.00E 02 Estimate 47 CH 3 SO 3 + H CO 3 SO 3 H + HO 2 + CO 1.60E 15 (Yin et al., 1990b) 48 CH 3 SO 3 + HO 2 3 SO 3 H + O 2 5.00E 11 (Yin et al., 1990b) 49 CH 3 SO 3 3 SO 3 H + NO 2 6.60E 16 (Yin et al., 1990b) 50 CH 3 SO 3 + H 2 O 2 3 SO 3 H + HO 2 3.00E 16 (Yin et al., 1990b) 51 CH 3 SO 3 + CH 3 3 SO 3 H + CH 3 O 2 3.00E 16 (Yin et al., 1990b) 52 CH 3 SO 3 + CH 3 3 SO 3 H + H CO H + HO 2 1.00E 16 (Yin et al., 1990b) 53 CH 3 SO 3 + NO 2 3 (O)S(O)ONO 2 3.00E 15 (Yin et al., 1990b) 54 CH 3 (O)S(O)ONO 2 + H 2 3 SO 3 H + HNO 3 1.00E 15 (Yin et al., 1990b) 55 CH 3 SO 3 3 (O)S(O)ONO 3.00E 15 (Yin et al., 1990b) 56 CH 3 (O)S(O)ONO + H 2 3 SO 3 H + HONO 1.00E 15 (Yin et al., 1990b) Wall loss 57 CH 3 S(O)CH 3 6.00E 05 Experiment 58 CH 3 (O)S(O)CH 3 7.00E 05 Experiment The unit for first order reactions is s 1 and the unit for second order reactions is s 1 molecules 1 cm 3

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115 Table A 2 DMS photooxidation mechanisms DMS Reaction Rate constant Note Initial reactions 59 CH 3 S CH 3 + OH 3 S CH 2 + H 2 O 1.13E 11exp( 254/T) (Atkinson et al., 1997) 60 CH 3 S CH 3 + OH 3 S(OH)CH 3 + M 1.70E 12 (Atkinson et al., 1989) 61 CH 3 S CH 3 + O 3 3 SO + CH 3 5E 11exp(0.0409/T) (Atkinson et al., 1989; Cvetanovic et al., 1981; Nip et al., 1981) 62 CH 3 S CH 3 + NO 3 3 S(ONO 2 )CH 3 1.4E 13exp(500/T) (Atkinson et al., 1989;Nip et al., 1981) 63 CH 3 S CH 3 + NO 2 3 S(O)CH 3 + NO 9.00E 21 (Balla and Heicklen, 1984) Primary products 64 CH 3 S(OH)CH 3 + O 2 3 S(O)CH 3 + HO 2 1.30E 12 (Barone et al., 1996) 65 CH 3 S(OH)CH 3 3 S OH + CH 3 5.00E+05 (Yin et al., 1990b) 66 CH 3 S(OH)CH 3 + O 2 3 S(OH)(OO)CH 3 1.00E 12 (Yin et al., 1990b) 67 CH 3 S CH 2 + O 2 3 S CH 2 OO 7.30E 13 (Schafer et al., 1978) 68 CH 3 S CH 2 + NO 3 3 S CH 2 OO + NO 3.00E 10 (Sander, 2006) 69 CH 3 S(ONO 2 )CH 3 3 S CH 2 + HNO 3 1.00E+02 (Yin et al., 1990) Secondary products a. DMSO b. Methylthiomethylperoxyl radical CH 3 SCH 2 O 2 70 CH 3 S CH 2 OO 3 S CH 2 O + NO 2 1.90E 11 (Nielsen et al., 1995) 71 CH 3 S CH 2 OO + CH 3 S CH 2 OO 3 S CH 2 O + O 2 8.60E 14 (Wallington et al., 1993) 72 CH 3 S CH 2 OO + HO 2 3 S CH 2 OOH 5.00E 12 (Nielsen et al., 1995) 73 CH 3 S CH 2 OO + CH 3 S 3 S CH 2 O + CH 3 SO 6.10E 11 (Yin et al., 1990b) 74 CH 3 S CH 2 OO + CH 3 SO 3 S CH 2 O + CH 3 (O)S(O) 4.00E 12 (Yin et al., 1990b) 75 CH 3 S CH 2 OO + CH 3 (O)S(O) 3 S CH 2 O + CH 3 SO 3 2.50E 13 (Yin et al., 1990b) 76 CH 3 S CH 2 OO + CH 3 O 2 3 S CH 2 O + CH 3 O + O 2 1.80E 13 (Yin et al., 1990b)

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116 Table A 2 Continued DMS Reaction Rate constant Note 77 CH 3 S CH 2 OO + NO 2 3 S CH 2 OONO 2 + M 9.20E 12 (Nielsen et al., 1995) c. CH 3 S(OH)(OO ) CH 3 78 CH 3 S(OH)(OO )CH 3 3 S(O)CH 3 + HO 2 1.00E+01 (Yin et al., 1990b) 7 9 CH 3 S(OH)(OO )CH 3 3 S(OH)(O)CH 3 + NO 2 5.00E 12 (Yin et al., 1990b) d. CH 3 S OH 80 CH 3 S 3 SO + H 2 O 1.10E 10 (Yin et al., 1990b) 81 CH 3 S OH + CH 3 SO 3 3 SO + CH 3 SO 3 H 3.40E 12 (Yin et al., 1990b) 82 CH 3 S OH + CH 3 O 3 SO + CH 3 OH 3.40E 12 (Yin et al., 1990b) 83 CH 3 S OH + O 3 3 SO + OH 3.40E 12 (Yin et al., 1990b) 84 CH 3 S OH + NO 3 3 SO + HNO 3 3.40E 12 (Yin et al., 1990b) 85 CH 3 S OH + HO 2 3 SO + H 2 O 2 8.50E 13 (Yin et al., 1990b) 86 CH 3 S OH + CH 3 O 2 3 SO + CH 3 OOH 8.50E 13 (Yin et al., 1990b) 87 CH 3 S OH+CH 3 S 3 S S(O)CH 3 + H 2 O 3.60E 18 (Yin et al., 1990b) Tertiary products a. CH 3 S(O)OH ( DMSO reactions) b. CH 3 S CH 2 O 88 CH 3 S CH 2 O 3 S + H CO H 2.00E+01 (Yin et al., 1990b) c. CH 3 S(OH)(O)CH 3 (DMSO reactions) d. CH 3 (O)S(O)CH 3 and its further reactions (DMSO reactions) Further products a. CH 3 S reactions 89 CH 3 S + O 2 3 SOO 5.80E 17 (Sander, 2006) 90 CH 3 SOO 3 S + O 2 6.00E+02 (Yin et al., 1990b)

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117 91 CH 3 S + O 3 3 SO + O 2 5.70E 12 (Domine et al., 1992)

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118 Table A 2 Continued DMS Reaction Rate constant Note 92 CH 3 S + NO 2 3 S NO 2 6.10E 13 (Yin et al., 1990b) 93 CH 3 S + NO 2 3 SO + NO 6.10E 11 (Yin et al., 1990b) 94 CH 3 S + 3 S NO 2.87E 11 (Balla et al., 1986) 95 CH 3 S + NO 3 3 SO + NO 2 6.40E 11 (Yin et al., 1990b) 96 CH 3 S + HO 2 3 SO + OH 3.00E 11 (Yin et al., 1990b) 97 CH 3 S + CH 3 O 2 3 SO + CH 3 O 6.10E 11 (Yin et al., 1990b) 98 CH 3 S + CH 3 S 3 S S CH 3 4.15E 11 (Graham et al., 1964) 99 CH 3 S + CH 3 S NO 3 S S CH 3 + NO 1.40E 12 (Yin et al., 1990b) 100 CH 3 S + OH 3 S OH 5.00E 11 (Yin et al., 1990b) 101 CH 3 S NO + h 3 S + NO 0.5*j[NO 2 _to_O 3 P] (Yin et al., 1990b) 102 CH 3 S.+ O 3 2 + CH 3 O 5.70E 12 (Domine et al., 1992) 103 CH 3 S.+ CH 3 S CH 3 +(O 2 3 .+CH 3 S(O)CH 3 + SO 8.00E 12 (Barnes et al., 1988) b. CH 3 SOO reactions 104 CH 3 SOO 3 SO + NO 2 1.10E 11 (Turnipseed et al., 1992) 105 CH 3 SOO + CH 3 S 3 SO 8.00E 11 (Yin et al., 1990b) 106 CH 3 SOO + CH 3 SO CH 3 SO + CH 3 (O)S(O) 9.00E 12 (Yin et al., 1990b) 107 CH 3 SOO + CH 3 (O)S(O) 3 SO +CH 3 SO 3 3.00E 13 (Yin et al., 1990b) 108 CH 3 SOO + HO 2 3 SOOH + O 2 4.00E 1 2 (Yin et al., 1990b) 109 CH 3 SOO + CH 3 O 2 3 SO + CH 3 O + O 2 5.50E 12 (Yin et al., 1990b) 110 CH 3 SOO + CH 3 SOO 3 SO +O 2 6.00E 12 (Yin et al., 1990b) c. CH 3 SO reactions 111 CH 3 SO + O 2 3 S(O)O O 7.70E 18 (Yin et al., 1990b) 112 CH 3 S(O)OO 3 SO + O 2 1.70E+02 (Yin et al., 1990b) 113 CH 3 SO + NO 2 3 (O)S(O) + NO 3.00E 12 MCM v3.2 114 CH 3 SO + NO 2 3 + NO + SO 2 3.00E 12 MCM v3.2

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119 Table A 2 Continued DMS Reaction Rate constant No te 115 CH 3 SO + CH 3 2.66E32*EXP( 25200/T) (Yin et al., 1990b) 116 CH 3 SO + NO 3 3 (O)S(O) + NO 2 8.00E 12 (Yin et al., 1990b) 117 CH 3 SO + O 3 3 (O)S(O) + O 2 1.00E 12 (Tyndall and Ravishankara, 1989) 118 CH 3 SO + HO 2 3 (O)S(O) + OH 1.50E 12 (Yin et al., 1990b) 119 CH 3 SO + CH 3 3 S +CH 3 (O)S(O) 7.50E 12 (Yin et al., 1990b) 120 CH 3 SO + CH 3 O 2 3 (O)S(O) + CH 3 O 3 .00E 12 (Yin et al., 1990b) 121 CH 3 SO + CH 3 S NO 3 S S(O)CH 3 + NO 6.80E 13 (Yin et al., 1990b) 122 CH 3 SO 3 S(O)OH 5.00E 11 (Yin et al., 1990b) 123 CH 3 SO + O 3 2 + CH 3 O 2 3.20E 13 (Borissenko et al., 2003) d. CH 3 (O)S(O) reactions (DMSO reactions) e. CH 3 S(O)OO reactions 124 CH 3 S(O)OO 3 (O)S(O) + NO 2 8.00E 12 (Yin et al., 1990b) 125 CH 3 S(O)OO + CH 3 S 3 (O)S(O) + CH 3 SO 7.00E 11 (Yin et al., 1990b) 126 CH 3 S(O)OO + CH 3 SO 3 (O)S(O) 8.10E 12 (Yin et al., 1990b) 127 CH 3 S(O)OO + CH 3 (O)S(O) 3 (O)S(O).+ CH 3 SO 3 3.00E 13 (Yin et al., 1990b) 128 CH 3 S(O)OO + CH 3 O 2 3 (O)S(O) + CH 3 O +O 2 5.50E 12 (Yin et al., 1990b) 129 CH 3 S(O)OO +CH 3 S(O)OO 3 (O)S(O) + O 2 6.00E 12 (Yin et al., 1990b) 130 CH 3 S(O)OO + NO 2 3 S(O)OONO 2 1 .00E 12 (Yin et al., 1990b) 131 CH 3 S(O)OONO 2 3 S(O)OO + NO 2 4.20E 03 (Yin et al., 1990b) f. CH 3 (O)S(O)OO reactions g. CH 3 SO 3 reactions 132 CH 3 SO 3 + CH 3 S CH 3 3 SO 3 H + CH 3 S CH 2 6.80E 13 (Yin et al., 1990b) h.CH 3 SONO 2 reactions 133 CH 3 S(O)NO 2 3 SO + NO 2 1.00 (Yin et al., 1990b) i.CH 3 reactions ( DMSO reactions)

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120 Table A 2 Continued DMS Reaction Rate constant Note j.CH 3 S(O)CH 2 and its fu r ther reactions 134 CH 3 S(O)CH 2 H 3 S + H CO H 1.00E+03 (Yin et al., 1990b) 135 CH 3 S(O)CH 2 + O 2 3 S(O)CH 2 OO 1.00E 12 (Yin et al., 1990b) 136 CH 3 S(O)CH 2 OO 3 S(O)CH 2 O + NO 2 6.00E 12 (Yin et al., 1990b) 137 CH 3 S(O)CH 2 OO + CH 3 S 3 SO + CH 3 S(O)CH 2 O 5.00E 11 (Yin et al., 1990b) 138 CH 3 S(O)CH 2 OO + CH 3 SO 3 (O)S(O) + CH 3 S(O)CH 2 O 4.00E 12 (Yin et al., 1990b) 139 CH 3 S(O)CH 2 OO + CH 3 (O)S(O) 3 SO 3 + CH 3 S(O)CH 2 O 2.50E 13 (Yin et al., 1990b) 140 CH 3 S(O)CH 2 OO + HO 2 2 + CH 3 S(O)CH 2 OOH 1.50E 12 (Yin et al., 1990b) 141 CH 3 S(O)CH 2 OO + CH 3 O 2 2 + CH 3 O + CH 3 S(O)CH 2 O 1.80E 13 (Yin et al., 1990b) 142 CH 3 S(O)CH 2 OO + CH 3 S(O)CH 2 OO 2 + 2CH 3 S(O)CH 2 O 8.60E 14 (Yin et al., 1990b) 143 CH 3 S(O)CH 2 O 3 SO + H CO H 1.00E+ 02 (Yin et al., 1990b) l.CH 3 SOH and CH 3 SO 2 H reactions (DMSO reactions) m.CH 3 S S CH 3 reactions 144 CH 3 S S CH 3 + OH 3 S OH + CH 3 S 5.59E 11exp(380/T) (Atkinson et al., 1989) 145 CH 3 S S CH 3 + O 3 3 SO + CH 3 S 5.62E 11exp(250/T) (Atkinson et al., 1989;Cvetanovic et al., 1981;Nip et al., 1981) 146 CH 3 S S CH 3 + NO 3 3 S(ONO 2 )S CH 3 7.00E 13 (Yin et al., 1990b) 147 CH 3 S(ONO 2 )S CH 3 3 S(O)NO 2 + CH 3 S 1.00E +02 (Yin et al., 1990b) 148 CH 3 S S CH 3 + h 3 S 5.0E 3*j[NO 2 _to_O 3 P] (Yin et al., 1990b) wall loss 149 CH 3 S CH 3 9.00E 06 Experiment 150 CH 3 S S CH 3 9.00E 06 Estimated The unit for first order reactions is s 1 and the unit for seco nd order reactions is s 1 molecules 1 cm 3

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121 Table A 3 SO 2 photooxidation mechanisms SO 2 Reactions Rate constant Note SO reactions 151 O 2 + SO 2 + O 3 P 1.39E 13exp( 2280/T) (Atkinson et al., 1989) 152 NO 2 + SO 2 + NO 1.40E 11 (Atkinso n et al., 1989) 153 O 3 + SO 2 + O 2 4.51E 12exp( 1170/T) (Atkinson et al., 1989) 154 O 3 P + SO 2 2.20E 11 (Graedel, 1977) 155 OH + SO 2 + HO 2 1.10E 10 (Graedel, 1977) 156 SO 3 + SO 2 2.00E 15 (Graedel, 1977) SO 2 reactions 157 O 3 P+ SO 2 3 9.75E 13exp( 1000/T) (Baulch et al., 1984; Kerr, 1984) 158 HO 2 + SO 2 3 + OH 1. 00E 18 (Atkinson et al., 1989; Atkinson and Lloyd, 1984) 159 CH 3 O 2 + SO 2 3 + CH 3 O 5.00E 17 (Atkinson et al., 1989;Atkinson and Lloyd, 1984) 160 CH 3 O + SO 2 3 O SO 2 5.50E 13 (Calvert, 1984) 161 C H 3 + SO 2 3 (O)S(O). 2.90E 13 (Graedel, 1977) 162 SO 2 + h 2 2*j[NO 2 _to_O 3 P] (Graedel, 1977) 163 OH + SO 2 2 9.07E 13exp (231/T) (Atkinson et al., 1989;Kerr, 1984) 164 NO 2 + SO 2 3 2.00E 26 (Sander, 2006) 165 NO 3 + SO 2 3 + NO 2 7.00E 21 (Sander, 2006) SO 2 reactions 166 SO 2 2 3.70E+06 (Graedel, 1977) 167 SO 2 *+ SO 2 3 6.30E 13 (Graedel, 1977) 168 SO 2 2 1 .10E 14 (Graedel, 1977) 169 HOSO 2 + O 2 2 + SO 3 4.00E 13 (Atkinson et al., 1989;Kerr, 1984) 170 HOSO 2 + OH 2 SO 4 + M 1.00E 11 (Graedel, 1979)

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122 Table A 3. Continued SO 2 Reactions Rate constant Note SO 3 reactions 171 SO 3 + H 2 2 SO 4 + M 9.10E 13 (Atkinson and Lloyd, 1984;Kerr, 1984) 172 SO 3 + O( 3 2 + O 2 7.00E 13 (Calvert et al., 1978) wall loss 173 SO 2 7.00E 06 Experiment The unit for first order reactions is s 1 and the unit for second order reactions is s 1 molecules 1 cm 3

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123 Table A 4 Comparison of the wall loss rates of different chemicals in this study and those in literature chemical wall loss rate in this study in literature DMS 9.010 6 1.510 6 (Yin et al., 1990a) SO 2 2.010 5 2.210 6 (Yin et al., 1990a) O 3 2.510 5 4.510 6 (Yin et al., 1990a) DMSO 6.010 5 3.310 5 (Ballesteros et al., 2002) DMSO 2 7.010 5 4.410 5 (Ballesteros et al., 2002) H 2 O 2 6.710 4 2.410 4 (Qi et al., 2007)

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124 Table A 5 I ntegrating r eaction rate (IRR) of the initial reactions of DMS decay in different conditions a No. b. Reaction iso DMS 1 iso DMS 2 iso DMS 3 59 CH 3 S CH 3 + OH 1.75 1.35 1.71 60 CH 3 S CH 3 + OH 0.61 0.48 0.6 61 CH 3 S CH 3 + O( 3 P) 1.18 1.62 2.37 62 CH 3 S CH 3 + NO 3 0.77 1.13 0.93 63 CH 3 S CH 3 + NO 2 0.01 0.01 0.01 103 CH 3 S.+ CH 3 S CH 3 0.96 0.96 1.26 132 CH 3 S CH 3 + CH 3 SO 3 0.51 0.49 0.47 a. Refer to Table 3 3 for the experimental conditions. b. Refer to Table S2 for the reaction number

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125 Figure A 1 Mass fragme ntation spectra in the EI mode (with GC retention time) for d6 DMSO, DMSO and DMSO 2

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126 Figure A 2 The time profiles of DMSO, DMSO 2 SO 2 NO x and O 3 for the photooxidation of DMSO in the presence of NO x (Exp DMSO 3 5 in Table 4 1). lly observed concentrations of chemical s model.

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127 Figure A 3 Model simulation of MSA and sulfuric acid for the photooxidation of DMSO in the presence of NO x (Exp DMSO 3 5 in Table 4 1) with (SH) and wit hout (SN) including heterogeneous reactions. experimentally observed concentrations of chemical s those simulated using the kinetic model.

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128 Figure A 4 The time profiles of DMS, DMSO 2 SO 2 MSA, sulfuric acid, NO x an d O 3 f or the photooxidation of DMSO in the presence of NO x (Exp DMS 1 2 in Table 4 1). chemical s model.

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129 Figure A 5 Mass fragmentation spectra in the EI mode (with GC retention time) for PFBHA derivatives of major carbonyl products originated from isoprene photooxidation in the presence of NO x P1: methacrolein (mono derivatives), P2: methyl vinyl ketone (mono derivatives), P3: glyoxal (di deriv atives), P4: methylglyoxal (di derivatives)

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130 Figure A 6 The time profiles of isoprene, P1 P4, NO x and O 3 from the photooxidation of isoprene in the presence of NO x (Exp iso 1 and iso 1 in Table 2). denotes the experimentally observed concentratio ns of chemical s pecies model.

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131 Figure A 7 The time profiles of gaseous products (P1 P4), NO x and O 3 from the photooxidation of DMS and NO x in the presence of 560 ppb of isoprene (Exp iso DMS 1), 1360 ppb of isoprene (Exp iso DMS 2) and 2248 ppb of isoprene (Exp iso DMS 3). concentrations of chemical s kinetic model.

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132 APPENDIX B SUPPLEME N TARY MATERIALS FOR CHAPTER 5 Table B 1 Relative intensities of EI mass spectra for BSTFA derivatives of 2 methyltetrols (P 1 ) and PFBHA derivatives of several carbonyls (P 2 P 5 ) Product ID Product Name a Retention time MW b PFBHA EI BSTFA EI M+181 M 181 M 197 M 225 73 117 129 147 219 277 4 09 P 1 2 methyltetrol 15.836, 16.096 424 c. n.a. n.a. n.a. n.a. 38.1 13.2 15 18.1 100 18.9 0.1 P 2 methacrolein 10.800, 10.864 265 8 2 1 n.a. n.a. n.a. n.a. n.a. n.a. n.a. P 3 methyl vinyl ketone 10.99, 11.05 265 0.4 1.5 5 0.8 n.a. n.a. n.a. n.a. n.a. n. a. n.a. P 4 glyoxal 20.010, 20.127 448 d 0.7 3.5 n.a. n.a. n.a. n.a. n.a. n.a. n.a. P 5 methylglyoxal 20.182, 20.498 462 d 0.9 21 0.1 n.a. n.a. n.a. n.a. n.a. n.a. n.a. a. P 1 ~ P 5 are named using common nomenclature b. The molecular weight of a PFBHA derivative increases the molecular weight of an underivatized compound by 195 c. The compound is di derivatized. d. The compound is di derivatized

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133 Table B 2 The ranges of the initial concentrations of DMS and NO (ppb) and MS / DMS_SO 4 2 ratios the in diff erent sites both in the morning and afternoon Gainesville Paynes Prairie Cedar Key from to from to from to Initial DMS 0.5 0.1 0.5 0.1 0.2 0.1 Initial NO 100 20 10 20 1 10 MS /SO 4 2 DMS in the morning 0.33 0.15 0.12 0.15 0.08 0.11 MS /SO 4 2 DMS in the afternoon 0.19 0.09 0.07 0.09 0.05 0.07

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134 Figure B 1. Linear regression of concentrations of the primary organic carbon versus concentrations of elementary carbon. The resulting slope and intercept were applied to decoupling of the OC into the primary and secondary OC. The slope and intercept are within 10% difference from those reported by Cabada et al. (2004)

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148 BIOGRAPHICAL SKETCH Tianyi Chen was born in Shanghai, China in 1986. Tianyi spent his first 22 years in Shanghai. Since high school, Tianyi was very active i n student activities related to environmental protection, wh ich made him decide to be dedicated to the environmental career. After earning the bachelor degree in environmental science, Tianyi came to US for air pollution research in the Department of Envi ronmental Engineering Sciences at the University of Florida. He received his Ph.D. from the University of Florida in the summer of 2012.