Georgia Tech Sponsored Research

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1 Georgia Tech Sponsored Research Project G Project director Wine Paul Research unit Title EAS Laboratory Studies of Tropospheric Sulfur Chemistry Project date 3/31/1999

2 Georgia Tech RESEARCH INSTITUTE May 16, 1995 Electro-Optics, Environment, and Materials Laboratory Georgia Tech Research Institute GeorgiaInstitute of Technology Atlanta, Georgia USA Dr. Sherry Farwell National Science Foundation Atmospheric Chemistry Program Division of Atmospheric Sciences Directorate for Astronomical, Atmospheric, Earth, and Ocean Sciences 4201 Wilson Blvd. Arlington, VA Dear Dr. Fnrwoll: Enclosed is the annual report for NSF grant ATM entitled "Laboratory Studies of Tropospheric Sulfur Chemistry.'' Two reprints of each of three journal articles and one book chapter published during the past year are enclosed. The requested budget of $142,000 for the period 9/1/95-8/31/96 is the amount approved in the original award letter. If there are any questions, I can be reached at (404) Best regards, Paul H. Wine Professor, School of Chem. & Biochem. Professor, School of Earth & Atmos. Sci. Principal Research Scientist, GTRI PHW:kb Enclosure Georgia Institute of Technology- is a unit of the University System of Georgia and an equal education/employment opportunity employer

3 ANNUAL NSF GRANT PROGRESS REPORT NSF Program: Atmospheric Chemistry NSF Award Number: ATM PI Name: Paul H. Wine Period Covarad By Thla Raport: 9/94-5/95 PMnatitution: Georgia Tech Data: May 19, 1995 PI Address: School of Chemistry and Biochemistry, Georgia Institute of Technology. Atlanta, GA Q Check if Continued Funding is Requested Please include the following information: 1 Brief summary of progress to date and work to be performed during the succeeding period; 2. Statement of funds estimated to remain unobligated -if more than 20%- at the end of the period for which NSF currently is providing support (not required for participants in the Federal Demonstration Project); 3 Proposed budget for the ensuing year in the NSF format, only if the original award letter did not indicate specific incremental amounts or if adjustments to a planned increment exceeding the greater of 10% or $10,000 are being requested, 4 Current information about other research support of senior personnel, if changed from the previous submission; 5. Any other significant information pertinent to the type of project supported by NSF or as specified by the terms and conditions of the grant, 6 A statement describing any contribution of the project to the area of education and human-resource development, if changed from any previous submission, and 7. Updated information on animal care and use, Institutional Biohazard Committee and Human Subject Certification, if changed substantially from those originally proposed and approved. 1. See attachments 2. All funds allocated for the period 9/94-8/95 will be spent by 8/31/ The requested budget for the period 9/95-8/96 is $142,000, the amount specified in the original award latter. 4. See attachments 5. Not applicable 6. See attachments 7. Not applicable I certify that to the best of my knowledge (1) the statements herein (excluding scientific hypotheses and scientific opinions) are true and complete, and (2) the text and graphics in this report as well as any accompanying publications or other documents, unless otherwise indicated, are the original work of the signatories or individuals working under their supervision. I understand that the willful provision of false information or concealing a material fact in this report or any other communication submitted to NSF is a criminal offense (U.S. Code, Title 18, Section 1001.) P.I. Signature: NSF Form 1328(1/94)

4 Progress During the Past Year During the past year, we have continued to make progress on detailed studies of the elementary steps in the atmospheric oxidation of dimethyl sulfide (DMS). In particular, we have investigated the kinetics and mechanisms for production of formaldehyde (H 2 CO) from CH 3 radicals in the presence of 0 2 and in both the presence and absence of NO; also, we have demonstrated that addition followed by rapid elimination of methyl radicals (CH 3 ) is not an important pathway for X + DMS reactions (X = OH or CI). We find that in the presence of NO, formaldehyde is produced with unit yield via the following reaction sequence: CH M -> CH M (1) CH NO -> CH N0 2 (2) CH M -» CH 3 S + H 2 CO + M (3) When 0 2 levels are sufficiently high, the rate-limiting step in H 2 CO production is found to be reaction (2) over the entire range of experimental conditions investigated. Our results clearly demonstrate that the lifetime of CH 3 0 toward dissociation to H 2 CO is no more than 30us at P = 10 Torr and T = 260K. Also, we obtain the following Arrhenius expression describing the temperature dependence of the rate coefficient for reaction (2): k 2 (T) = 4.9 x 10' 12 exp (260/T) cm 3 molecule's" 1 ; our room temperature rate coefficient of 1.2 x 10' 11 cm 3 molecule's" 1 is 50% lower than the only published value [Wallington et al., J. Phys. Chem. 97, 8442 (1993)]. In the absence of NO, we find that formaldehyde is produced with near unit yield via the CH self reaction, i.e., reaction (4a) followed by reaction (3): 2 CH > 2 CH > CH 3 OH + CH 3 SCHO » CH 3 OOCH 2 SCH (4a) (4b) (4c)

5 Experiments aimed at quantitatively measuring the rate coefficient k 4 (= k 4a + k 4b + k^) are still in progress; it appears that k 4 is significantly faster than the value 7.9 x 10" 12 cm'moleculev 1 reported by Wallington et al. [J. Phys. Chem. 97, 8442 (1993)]. In addition to the studies of DMS oxidation described above, we have studied CO production from 248 nm photodissociation of OCS. Unlike previous reports [Sidhu et al, J. Am. Chem. Soc. 88, 2412 (1966); Rudolph and Inn, J. Geophys. Res. 86> 9891 (1981)], we find that the quantum yield for CO production (which equals the quantum yield for OCS destruction) is unity. This result has important implications for evaluating the role of OCS as a precursor to the lower stratospheric sulfate aerosol layer. The third research track we have pursued during the past year has been construction of an apparatus which couples laser flash photolysis (LFP) with time-resolved detection of reactants and products by photoionization mass spectrometry (PIMS). The main chamber and pumping system have been assembled, and a majority of the machining work has now been completed. We hope to have the LFP-PIMS apparatus fully operational by the end of Publications Acknowledging NSF Support, 6/94-present 1. Temperature-dependent kinetics studies of the reactions Br( 2 P 3/2 ) + CH 3 SCH 3 <-» CH 3 + HBr. Heat of formation of the CH 3 radical, A. Jefferson, J. M. Nicovich, and P. H. Wine, J. Phys. Chem. 98, 7128 (1994). 2. Quantum yield for carbon monoxide production in the 248 nm photodissociation of carbonyl sulfide (OCS), Z. Zhao, R. E. Stickel, and P. H. Wine, Geophys. Res. Lett. 22, 615 (1995). 3. Kinetics of the reactions of atomic chlorine with H 2 S, D 2 S, CH 3 SH, and CD 3 SD, J. M. Nicovich, S. Wang, and P. H. Wine, Int. J. Chem. Kinet. 27, 359 (1995).

6 4. Sulfur in the atmosphere, H. Berresheim, P. H. Wine, and D. D. Davis, in Composition, Chemistry, and Climate of the Atmosphere, ed. By H. B. Singh, Van Nostrand Reinhold, pp (1995). Two reprints of each of the above publications are enclosed. Plans for the Upcoming Year During the upcoming year we plan to pursue the following lines of research: (1) We plan to employ the LFP-TDLAS (tunable diode laser absorption spectroscopy) technique to investigate CH 3 production in X + DMSO reactions (X = OH, CI, and N0 3 ), and to investigate the kinetics and thermochemistry of the reactions of CH 3 radicals with S0 2 and S0 3. The rationale for these studies was discussed in our original proposal. (2) We plan to employ the LFP-PLIF (pulsed laser induced fluorescence) technique to measure the yield of SO from the CS 2 OH reaction, and to study the atmospheric chemistry of thioformaldehyde (H 2 CS). A recent smog chamber study by Barnes el al [Geophys. Res. Lett. 2J_, 2389 (1994)] suggests that H 2 CS may be an important intermediate in DMS oxidation. We will investigate the slow CH 3 S reaction as a possible source of H 2 CS, as well as the mechanism for conversion of H 2 CS to the more stable species OCS and (possibly) S0 2. (3) We will complete construction of the LFP-PLMS apparatus, and will initiate studies of the chemistry of CH and CH 3 SO x radicals employing the LFP-PIMS technique. The rationale for these studies was discussed in our original proposal. Contribution to Education and Human Resource Development Two graduate students, Zhizhong Zhao and Shawn Urbanski, have been supported on this project. Mr. Zhao defended his dissertation in March, 1995 and will officially receive his Ph.D. degree at Georgia Tech's June commencement; the title of his dissertation is "Laboratory Studies

7 of the Atmospheric Oxidation of Dimethyl Sulfide Using Laser Flash Photolysis Coupled with Tunable Diode Laser Absorption Spectroscopy". Mr. Urbanski, a second year student in the School of Earth and Atmospheric Sciences, is building on Zhao's efforts and also getting involved in the LFP-PLIF studies. Charles Piety, a second year graduate student in the School of Chemistry and Biochemistry, has become involved in construction of the LFP-PIMS apparatus; he plans to make LFP-PIMS studies of atmospheric sulfur chemistry his dissertation topic. Mr. Piety will be supported on this project beginning in October, Research Support of Senior Personnel See attached copies of NSF form 1239

8 CURRENT AND PENDING SUPPORT TtwtotowtngInformationthouWtoprovidedtor efttivrtg«iofandothernrfcfperenat.f«mur*toprovm*w»information OtheraganeiMOndudhgNSF)towhichIN*prepceafha*tow** toaubm Investigator; Support Curent PaulH.Wine 0Pending SubmisionPlaned none innearfuture TransferofSupport Project/Proposal. itle: LaboratoryStudiesofTropospheric SulfurChemistry SourceofSupport:NSF-AtmosphericChemistryProgram AwardAmount LocationofResearch:MainGeorgiaTechCampus Support Curent (orannualrate): Pending $60, SubmisionPlaned 0 PeriodCovered:9/1/94 innearfuture TransferofSuppo -8/31/98 Project/Proposal Person-Monthsor Title: %ofefortcommutedtotheproject Cat Acad: Summ: i.00 MOS Laboratory InvestigationsofStratosphericHalogenChemistry SourceOfSupport:NASA-UperAtmosphereResearchProgram AwardAmount LocationOfResearch:MainGeorgiaTechCampus (orannualrate): $461,000 PeriodCovered:1/1/93-12/31/95 Project/Proposal Support Curent Person-Monthsor Title: Pending SubmisionPlaned innearfuture TransferofSuppo ComparativeStudyoftheAtmospheric %ofeftortcommitedtotheproject.ceil: SulfurBudget in DiferentNaturalEnvironm Acad: Summ: 1-25m SourceOfSupport:NSF-AtmosphericChemistryProgram AwardAmount (orannualrate): $ 19, 0 PeriodCovered:10/15/93-3/31/96 LocationOfResearch: Person-Monthsor %ofefortcommitedtotheproject.cat: MainGeorgiaTechCampus Support Curent Pending SubmisionPlaned innearfuture Acad: TransferofSuppo Summ:0.50 Project/Proposal Title: LaboratoryStudiesofPhotochemicalOzoneProduction inthetroposphere SourceOfSupport:EPA-0fice ofexploratoryresearch LocationOfResearch: AwardAmount (orannualrate): M $443,453 PeriodCovered:10/1/95-9/30/98 3 * 1 GeorgiaTechCampus Person-Monthsor Support Curent %ofefortcommitedtotheprojectcal: Pending SubmisionPlaned innearfuture Acad:1.00mo TransferofSuppo Project/Proposal Title:.Summ: Experimentaland SinksofNitrousOxide TheoreticalStudies of PotentialNewAtmosphericSourcesand SourceOfSupport:NSF-AtmosphericChemistryProgram AwardAmount LocationOfResearch: (orannualrate): MainGeorgiaTechCampus $15*,684 (G.T.share)PeriodCovered:10/1/95-9/30/97 M Person-Monthsor tfeprotecthaspreviouslybenfundedbyanotheragency,please %ofefortcommitedtotheproject.cal: listandfurnishinformationtorimmediatelyprec Acad: Summ:0.50m NSFForm1239 (8/92) USEADDITIONALSHETSASNEC

9 Tr»tes»wlrigHorrn*tionahouW* Investigator: Robert E. Stickel Current and Pending Support to P*"** ** Wormatton may delay eonekton^ cl tat proposal. O0W agenda* (Indudinfl NSF)towhich trat prepoml has beervwa ba submitted. none -Support Current Pending Submission Planned in Near Future Transfer of Support Project/Proposal Title: Laboratory Studies of Tropospheric Sulfur Chemistry Source Of Support NSF-Atmospheric Chemistry Program Award Amount (or Annual Rate): $ 600,000 Period Covered: 9/1/94-8/31/98 Location of Research: Main Georgia Tech Campus Person-Months or % of Effort Committed to the Project Cal: 2 S mosacad: Summ: Support Current Pending Submission Planned in Near Future Transfer of Support Project/Proposal Title: Laboratory Investigations of Stratospheric Halogen Chemistry Source Of Support: NASA-Upper Atmosphere Research Program Award Amount (or Annual Rate): $ 461,000 Period Covered: 1/1/93-12/31/95 Location of Research: Person-Months or % of Effort Committed to the Project. Cal:2.0 mos. Acad: Summ: Support Current m Pending Submission Planned In Near Future Transfer of Support Project/Proposal Title: Laboratory Studies of Photochemical Ozone Production in the Troposphere Source Of Support: EPA-Office of Exploratory Research Award Amount (or Annual Rate): $ 443,453 Period Covered: 10/1/95-9/30/98 Location Of Research: Main Georgia Tech Campus Person-Months or % of Effort Committed to the Project. Cal;2.0 mos Acad: Summ: Support: Current Pending Submission Planned In Near Future Transfer of Support Project/Proposal Title: Experimental and Theoretical Studies of Potential New Atmospheric Sources and Sinks of Nitrous Oxide Source Of Support: NSF-Atmospheric Chemistry Program Award Amount (or Annual Rate): $ 154,684 (G.T. share) Period Covered: 10/1/95-9/30/97 Location Of Research: Main Georgia Tech Campus Person-Months or % of Effort Committed to the Project. Cal:3.0 mos. Acad: Summ: Support Current O Pending Submission Planned in Near Future Transfer of Support Project/Proposal Title: Source of Support: Award Amount (or Annual Rate): $ Period Covered: Location of Research: Person-Months or % of Effort Committed to the Project. Cal: Acad: Summ: *tl this project has previously been funded by another agency, please list and furnish Information lor Immediately preceding funding period. NSF Form 1238(6782) USE ADDITIONAL SHEETS AS NECESSARY

10 Current and Pending Support Thefollowing information should be providedforeachinvestigator othar Mnfor parsonnal. Failureto provide tn* Information may delay consideration ofthis proposal. Othar agendas (Including NSF)to whichthis proposal hat beetvwm Da submitted. Investigator: J. Michael Nicovich none Support: Current Pending Submission Planned in Near Future 'Transfer of Support Project/Proposal Title: Laboratory Studies of Tropospheric Sulfur Chemistry Source Of Support: NSF-Atmospheric Chemistry Program Award Amount (or Annual Rate): $ 600,000 Period Covered: 9/1/94-8/31/98 Location of Research: Main Georgia Tech Campus Person-Months or % of Effort Committed to the Project. Cal: 2.5 Acad: Summ: Support: Current Pending Submission Planned in Near Future 'Transfer of Support Project/Proposal Title: Laboratory Investigations of Stratospheric Halogen Chemistry Source Of Support: NASA-Upper Atmosphere Research Program Award Amount (or Annual Rate): $ 461,000 Period Covered: 1/1/93-12/31/95 Location of Research: Main Georgia Tech Campus Person-Months or % of Effort Committed to the Project. Cal: 3.0 Acad: Summ: Support: Current Pending Submission Planned in Near Future 'Transfer of Support Project/Proposal Title: Laboratory Studies of Photochemical Ozone Production in the Troposphere Source Of Support: EPA-Office of Exploratory Research Award Amount (or Annual Rate): $443,453 Period Covered: 10/1/95-9/30/98 Location of Research: M a i n G e o r g i a T e c h Campus Person-Months or % of Effort Committed to the Project. Cal: 3.0 Acad: Summ: Support: Current Pending Submission Planned in Near Future* 'Transfer of Support Project/Proposal Title: Source of Support: Award Amount (or Annual Rate): $ Location of Research: Period Covered: Person-Months or % of Effort Committed to the Project. Cal: Acad: Summ: Support: Current Pending Submission Planned in Near Future 'Transfer of Support Project/Proposal Title: Source of Support: Award Amount (or Annual Rate): $ Location of Research: Period Covered: Person-Months or % of Effort Committed to the Project. Cal: Acad: Summ: *H this project has previously been funded by another agency, pleaselist and furnish Information tor Immediately preceding funding period. NSF Form 1239 (8/92) USE ADDITIONAL SHEETS AS NECESSARY

11 ANNUAL NSF GRANT PROGRESS REPORT NSF Program: Atmospheric Chemistry NSF Award Number: ATM PI Name: Paul H. Wine Period Covered By This Report: 6/95-5/96 PI Organization: Georgia Tech Date: May 20, 1996 PI Address: School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, Georgia jd Checkif Continued Fundingis Requested Please include the following information: 1. Brief summary of progress, including results obtained to date, and their relationship to the general goals of the grant; 2. A brief summary' of work to be performed during the next year of support if changedfrom the original proposal; an indication of any current problems or favorable or unusual developments; and any other significant information pertinent to the type of project supported by NSF or as specified by the terms and conditions of the grant; 3. Statement of funds estimated to remain unobligated if more than 20% at the end of the period for which NSF currentlyis providing support; 4. Proposed budget for the ensuing year in the NSF format, only if the original award letter did not indicate specific incremental amounts or if adjustments to a planned increment exceeding the greater of 10% or $10,000 are being requested; 5. Information about other current and pending research support of senior personnel, if changedfrom the previous submission. 5. A statement describing any contribution of the project to the area of education and human-resource development, if changedfromany previous submission; and 7. Updated information on animal care and use, Institutional Biohazard Committee and Human Subject Certification, if changed substantiallyfrom those originally proposed and approved. 1. See attachments. 2. All funds allocated for the period 9/95-8/96 will be spent by 8/31/ The requested budget for the period 9/96-8/97 is $142,000, the amount specified in the original award letter. 4. See attachments 5. Not applicable 6. See attachemnts 7. Not applicable I certify that to the best of my knowledge (1) the statements herein (excluding scientific hypotheses and scientific opinions) are true and complete, and (2) the text and graphics in this report as well as any accompanying publications or other documents, unless otherwise indicated, are the original work of the signatories or individuals working under their supervision. I understand that the willful provision of false information or concealing a materialfact in this report or any other communication submitted to NSFis a criminal offense (U.S. Code, Title 18, Section 1001.) PI Signature: /2M 0.. NSF Form 1328 (7/95)

12 Progress During the Past Year During the past year, we have continued to make progress on detailed studies of the elementary steps in the atmospheric oxidation of dimethyl sulfide (DMS). In particular, we have completed our studies of H 2 CO production from CH 3 radicals in the presence of 0 2, but in the absence of NO (studies carried out with NO present were discussed in our last annual report). In addition, we have carried out a detailed investigation aimed at assessing some aspects of the atmospheric chemistry of CH 3 S0 2 radicals. In our studies of H 2 CO production, CH radicals were generated as follows: Cl 2 CO + hv(248 nm) CI + CH 3 SCH 3 CH CI + CO CH 3 + HC1 (CH 3 ) 2 SCI CH ) (2a) (2b) (3) In the absence of NO, the predominant fate of CH is self-reaction: 2 CH,SCH,0 2w 2 2 H 2 CO + 2 CH 3 S (4a) CH 3 SCHO + CH 3 OH (4b) CH 3 OOCH 2 SCH (4c) We find that H 2 CO is produced in near unit yield, thus demonstrating that k^/l^ ~ 1. In addition, we find that the rate coefficient k 4 is quite fast, i.e., k 4 (298K) = 1.3 x 10" 11 cn^molecule^s" 1 ; this rate coefficient is fast enough to make reaction (4) potentially significant under remote marine boundary layer conditions, where NO x levels are typically very low. The importance of reaction (4) in atmospheric chemistry will depend on how effectively it competes with reaction (5). CH HO CH 3 SCH,OOH + O, (5) One of our goals during the remainder of this project is to carry out a detailed study of the

13 kinetics of reaction (5). The above-mentioned study of reaction (4) lays the groundwork for the future study of reaction (5). The CH 3 S0 2 radical is a key intermediate in most proposed mechanisms for oxidation of atmospheric DMS. The role of DMS oxidation in global climate regulation depends critically on the yield of H 2 S0 4 (g) from the oxidation process. The CH 3 S0 2 radical could be an important "branch point" in the overall oxidation mechanism. If CH 3 S0 2 thermally decomposes to CH 3 + S0 2, very little production of H 2 S0 4 (g) would be expected; this is because, under marine boundary layer conditions, S0 2 is destroyed primarily by uptake into cloud and aerosol droplets, followed by condensed phase oxidation. On the other hand, if CH 3 S0 2 is sufficiently stable toward unimolecular decomposition, it could be oxidized to CH 3 S0 3 via reaction with 0 3, N0 2, and ultimately converted to H 2 S0 4 (g) with high yield. Literature values for the heat of formation of CH 3 S0 2 span a wide range [Busfield et al., Trans. Far. Soc. 5_7,1064 (1961); Good and Thynne, J.C.S. Far. Trans. 63, 2708 (1967); Davis, J. Phys. Chem. 9J7, 8442 (1993)]; hence, new information concerning CH 3 S0 2 thermochemistry and kinetics is needed before the role of this species in atmospheric sulfur chemistry can be established. Over the past year, we have invested considerable effort in a study aimed at assessing the stability of CH 3 S0 2 by studying the temperature and pressure dependences of its formationdissociation kinetics. CH 3 + S0 2 + M «-> CH 3 S0 2 + M (5,-5) The experiment involves time-resolved detection of CH 3 (using tunable diode laser absorption spectroscopy) following generation of CH 3 by laser flash photolysis of CH 3 I or C1 2 /CH 4. Based on available information from the literature, the above approach seemed likely to succeed in yielding temperature and pressure dependent values for both k 5 and k. 5. However, our results have been somewhat surprising. We find that k 5 (298K) = 3.4 x 10' 14 cm 3 molecule', s" 1, i.e., nearly an order of magnitude slower than values reported by Calvert et al. [in Chemical Reactions in the Urban Atmosphere (1971)] and James et al. [J.C.S. Far. Trans. I, 2124 (1973)]. We also observe a rather large negative activation energy for k 5 (T), suggesting the possibility that the reaction

14 mechanism may be more complex than a simple addition of the carbon atom on methyl to the sulfur atom on S0 2. Finally, despite our best efforts, we have not yet been able to observe evidence for CH 3 S0 2 decomposition,i.e., regeneration of CH 3 on the millisecond experimental time scale. Another research track we have pursued during the past year has involved construction of an apparatus which couples laserflashphotolysis (LFP) with time-resolved detection of reactants and products by photoionization mass spectrometry (PIMS). However, work on development of the LFP-PIMS apparatus has been slowed because the student who was working on this project * decided to drop back from the Ph.D. program to the Masters program and, as a result, switched to an shorter-term project. Hence, construction and shakedown of the LFP-PIMS apparatus will extend into the next year. Publications Acknowledging NSF Support, 1/95-present 1. Quantum yield for carbon monoxide production in the 248ranphotodissociation of carbonyl sulfide (OCS), Z. Zhao, R. E. Stickel, and P. H. Wine, Geophys. Res. Lett. 22, 615 (1995). 2. Kinetics of reactions of atomic chlorine with H 2 S, D 2 S, CH 3 SH, and CD 3 SD, J. M. Nicovich, S. Wang, and P. H. Wine, Int. J. Chem. Kinet. 27, 359 (1995). 3. Sulfur in the Atmosphere, H. Berresheim, P. H. Wine, and D. D. Davis, in Composition. Chemistry, and Climate of the Atmosphere, ed. by H. B. Singh, Van Nostrand Reinhold, pp (1995). 4. A mechanistic study of the reaction of OH with dimethyl-d 6 sulfide. Direct observation of adduct formation and the kinetics of the adduct reaction with 0 2, A. J. Hynes, R. B. Stroker, A. J. Pounds, T. McKay, J. D. Bradshaw, J. M. Nicovich, and P H. Wine, J. Phys. Chem. 99_, (1995). 5. Branching ratios for methyl elimination in the reactions of OD radicals and CI atoms with CH 3 SCH 3, Z. Zhao, R. E. Stickel, and P. H. Wine, Chem. Phys. Lett. 25_L 59 (1996). 6. The atmospheric chemistry of dimethylsulfoxide (DMSO). Kinetics and mechanism of the OH + DMSO reaction, A. J. Hynes and P. H. Wine, J. Atmos. Chem., in press.

15 Reprints of the first three publications were submitted with our last annual report. Two reprints each of publications 4 and 5 are enclosed. Plans for the Upcoming Year During the upcoming year, we plan to continue to pursue several lines of reasearch relating to atmospheric sulfur chemistry. These include the following: (1) We will complete our study of the CH 3 + S0 2 + M CH 3 S0 2 + M reactions and will initiate similar studies of the CH 3 + S0 3 + M <-* CH 3 S0 3 + M reactions. (2) We will initiate a series of studies where the LFP-TDLAS (tunable diode laser absorption spectroscopy) technique will be employed to investigate CH 3 production in X + DMSO reactions (X = OH, CI, and N0 3 ). (3) We will continue to work on development of LFP-PIMS technique with the long-range goal of applying this approach to kinetic and mechanistic studies of large organo-sulfur radicals. (4) We will initiate a study of the kinetics of the CH H0 2 reaction. The experimental approach will couple radical production by laser flash photolysis with simultaneous detection of CH and H0 2 using a combination of UV and IR timeresolved absorption techniques. (5) We plan to inititate a series of LFP-PLIF (pulsed laser induced fluorescence) experiments to investigate several aspects of atmospheric sulfur chemistry. Two of the higher priority experiments include measurement of the yield of SO from the CS 2 OH reaction and investigation of the atmospheric chemistry of thioformaldehyde (H 2 CS). A recent smog chamber study by Barnes et al. [Geophys. Res. Lett. 21,2389 (1994)] suggests that H 2 CS may be an important intermediate in DMS oxidation. We will investigate the slow CH 3 S reaction as a possible source of H 2 CS, as well as the mechanism for conversion of H 2 CS to the more stable species OCS and (possibly) S0 2.

16 Contribution to Education and Human Resource Development listed below. Several graduate students have been supported fully or in part on this project. They are Edgar G. Estupinan, Earth and Atmospheric Sciences Virginia M. Ferrell, Chemistry and Biochemistry Charles A. Piety, Chemistry and Biochemistry Shawn P. Urbanski, Earth and Atmospheric Sciences Zhizhong Zhao, Earth and Atmospheric Sciences Zhao received his Ph.D. in June 1995; his dissertation was entitled "Laboratory Studies of the Atmospheric Oxidation of Dimethyl Sulfide Using Laser Flash Photolysis Coupled with Tunable Diode Laser Absorption Spectroscopy." Estupinan and Urbanski are Ph.D. Students while Ferrell and Piety are Thesis Masters Students. Research Support of Senior Personnel See attached copies of NSF form 1239.

17 CURRENT AND PENDING SUPPORT (See GPG Section II.D.8 for guidance on information to include on this form.) The following information should be providedfor each investigator and other senior personnel. Failure to providethis information may delay considerationofthis propos Investigator: P a u l H_ W i n e Other agencies (including NSF) to which this proposal has been/will be submitted. Support: Current Pending Submission Planned in Near Future 'Transfer of Support Project/Proposal Title: Laboratory Studies of Tropospheric Sulfur Chemistry Source Of Support: NSF-Atmospheric Chemistry Program Total Award Amount: $600K Total Award Period Covered: 9/1/94-8/31/98 Location of Project: Main Georgia Tech Campus Person-Months Per Year Committed to the Project. Cal: Acad: Sumr: 1.00 Support: I Current D Pending D Submission Planned in Near Future D 'Transfer of Support Project/Proposal Title: Laboratory Investigations of Stratospheric Halogen Chemistry Source of Support: NASA - Upper Atmosphere Research Program Total Award Amount: $ 1308K Total Award Period Covered: 1/1/87-12/31/96 Location of Project: Main Georgia Tech Campus Person-Months Per Year Committed to the Project. Cal: Acad: Sumr: 1.00 Support: D Current I Pending D Submission Planned in Near Future D 'Transfer of Support Project/Proposal Title: Experimental and Theoretical Studies of Potential New Atmospheric Sources and Sinks of Nitrous Oxide Source Of Support: NSF - Atmospheric Chemistry Program via sub-grant from Creative Research Enterprises Total Award Amount: $135K Total Award Period Covered: 6/1/96-5/31/98 Location of Project: Main Georgia Tech Campus Person-Months Per Year Committed to the Project. Cal: Acad: Sumr: 0.40 j Support: D Current I Pending D Submission Planned in Near Future D'Transfer of Support! Project/Proposal Title: Use of Computational Molecular Modeling Methods for Determining the the Reaction Pathways of Environmental Organic Compounds : An Integrated Modeling and Laboratory Exploration...(joint with A. Russell, J. Mulholland, and R. Borkman)! Source Of Support: EPA - Office of Research and Development Total Award Amount: $378K Total Award Period Covered: 10/1/96-9/30/99 Location of Project: Main Georgia Tech Campus Person-Months Per Year Committed to the Project. Cal: Acad: 1-00 Sumr: Support: D Current D Pending D Submission Planned in Near Future D 'Transfer of Support Project/Proposal Title: Source of Support: Total Award Amount: $ Location of Project: Total Award Period Covered: Person-Months Per Year Committed to the Project. Cal: Acad: Sumr: "If this project has previously been funded by another agency, pleaselist and furnish informationlor immediately preceding funding period. NSF Form 1239 (7/95) USE ADDITIONAL SHEETS AS NECESSARY

18 CURRENT AND PENDING SUPPORT (See GPG Section II.D.8 for guidance on information to include on this form.) THEFOLOWINGINFORMATIONSHOULDBEPROVIDEDFOREACHINVESTIGATORANDOTHERSENIORPERSONNEL.FAILURETOPROVIDETHISINFORMATIONMAYDELAYCONSIDERATION Investigator: ROBERT E. STICKEL OTHERAGENCIES (INCLUDING NSF)TOWHICHTHISPROPOSALHASBEEN/WILLBESUBMITTED. Support: Current Pending Submission Planned in Near Future Transfer of Support Project/Proposal Title: LABORATORY STUDIES OF TROPOSPHERIC SULFUR CHEMISTRY Source of Support: NSF - ATMOSPHERIC CHEMISTRY PROGRAM Total Award Amount: $600K Total Award Period Covered: 9/1/94-8/31/98 Location of Project: MAIN GEORGIA TECH CAMPUS Person-Months Per Year Committed to the Project. Cal: 2.00 Acad: Sumr: Support: I Current Pending Submission Planned in Near Future D Transfer of Support Project/Proposal Title: LABORATORY INVESTIGATIONS OF STRATOSPHERIC HALOGEN CHEMISTRY Source of Support: NASA - UPPER ATMOSPHERE RESEARCH PROGRAM Total Award Amount: $1308K Total Award Period Covered: 1/1/87-12/31/96 Location of Project: MAIN GEORGIA TECH CAMPUS Person-Months Per Year Committed to the Project. Cal: 1.50 Acad: Sumr: Support: D Current I Pending D Submission Planned in Near Future D Transfer of Support Project/Proposal Title: EXPERIMENTALAND THEORETICAL STUDIES OF POTENTIALNEW ATMOSPHERIC SOURCES AND SINKS OF NITROUS OXIDE Source Of Support: NSF - ATMOSPHERIC CHEMISTRY PROGRAM VIA SUB-GRANT FROM CREATIVE RESEARCH ENTERPRISES [Total Award Amount: $ 135K Total Award Period Covered: 6/1/96-5/31/98 I Location of Project: MAIN GEORGIA TECH CAMPUS Person-Months Per Year Committed to the Project. Cal: 2.50 Acad: Sumr: ; Support: D Current H Pending D Submission Planned in Near Future D Transfer of Support Project/Proposal Title: DATA ANALYSIS FOR ACE-I FIELD PROGRAM : AMMONIAAND NO MEASUREMENTS!Source of Support: NSF - ATMOSPHERIC CHEMISTRY PROGRAM VIA SUB-GRANT FROM G.T. SCHOOL OF EARTH & ATMOS. SCI. : Total Award Amount: $ 42K Total Award Period Covered: Location of Project: Person-Months Per Year Committed to the Project. Cal: 2.50 Acad: Sumr: Support: Current Pending Submission Planned in Near Future Transfer of Support Project/Proposal Title: Source of Support: Total Award Amount: $ Total Award Period Covered: Location of Project: Person-Months Per Year Committed to the Project. Cal: Acad: Sumr: *LFTHISPROJECTHASPREVIOUSLYBEENFUNDEDBYANOTHERAGENCY,PLEASELISTANDFURNISHINFORMATIONFORIMMEDIATELYPRECEDINGFUNDINGPERIOD. NSFFORM 1239 (7/95) USE ADDITIONAL SHEETS AS NECESSARY

19 CURRENT AND PENDING SUPPORT (See GPG Section II.D.8 for guidance on information to include on this form.) Thefollowing information should be providedfor eachinvestigator ana other senior personnel. Failure to providethis information may delay consideration ofthis proposa Investigator: J. Michael Nicovich Other agencies (including NSF) to which this proposal has been/will be submitted. Support: Current Pending Submission Planned in Near Future 'Transfer of Support Project/Proposal Title: Laboratory Studies of Tropospheric Sulfur Chemistry Source Of Support: NSF - Atmospheric Chemistry Program Total Award Amount: $ 600K Total Award Period Covered: 9/1/94-8/31/98 Location of Project: Main Georgia Tech Campus Person-Months Per Year Committed to the Project. Cal: 2.50 Acad: Sumr: Support: I Current Pending Submission Planned in Near Future 'Transfer of Support Project/Proposal Title: Laboratory Investigations of Stratospheric Halogen Chemistry Source of Support: NASA - Upper Atmosphere Research Program Total Award Amount: $ 1308K Total Award Period Covered: 1/1/87-12/31/96 Location of Project: Main Georgia Tech Campus Person-Months Per Year Committed to the Project. Cal: 2.50 Acad: Sumr: Support: Current Project/Proposal Title: Pending Submission Planned in Near Future 'Transfer of Support Source of Support: Total Award Amount: $ Location of Project: Total Award Period Covered: Person-Months Per Year Committed to the Project. Cal: Acad: Sumr: Support: Current 'roject/proposal Title: Pending Submission Planned in Near Future 'Transfer of Support Source of Support: Total Award Amount: $ Location of Project: Total Award Period Covered: Person-Months Per Year Committed to the Project. Cal: Acad: Sumr: Support: Current 'roject/proposal Title: Pending Submission Planned in Near Future 'Transfer of Support Source of Support: iotal Award Amount: $ Location of Project: Total Award Period Covered: erson-months Per Year Committed to the Project. Cal: Acad: Sumr: If this project has previously been funded by another agency, pleaselist and furnish informationfor immediately preceding funding period. NSF Form 1239 (7/95) USE ADDITIONAL SHEETS AS NECESSARY

20 Georgia Tech May 30, 1997 School of Chemistry and Biochemistry Georgia Institute of Technology Atlanta, Georgia USA * *7452 Fax 3 Dr. Anne-Marie Schmoltner National Science Foundation Division of Atmospheric Sciences Atmospheric Chemistry Program 4201 Wilson Boulevard, Room 775 Arlington, VA AntVL- fjkful. Dear -Dr. Schmoltner: Enclosed is the annual report for NSF grant no. ATM Yours Truly, Paul H. Wine Professor, School of Chemistry and Biochemistry Professor, School of Earth and Atmospheric Sciences Principal Research Scientist, GTRI PHW/mwm Enclosure An Equal Education and Employment Opportunity institution A Unit of the University System of Georgia

21 ANNUAL NSF GRANT PROGRESS REPORT N S F P r o g r a m : A t m o s p h e r i c C h e m i s t r y N S F A w a r d N u m b e r : A T M P I N a m e : P a u l H. W i n e P e r i o d C o v e r e d B y T h i s R e p o r t : 6 / / 9 7 P I O r g a n i z a t i o n : G e o r g i a T e c h D a t e : M a y 3 0, P I A d d r e s s : S c h o o l o f C h e m i s t r y a n d B i o c h e m i s t r y, G e o r g i a I n s t i t u t e o f T e c h n o l o g y, A t l a n t a, G A E C h e c k if C o n t i n u e d F u n d i n g is R e q u e s t e d P l e a s e i n c l u d e t h e f o l l o w i n g i n f o r m a t i o n : 1. B r i e f s u m m a r y o f progress, including results obtained to date, a n d their relationship to the general g o a l s o f the grant; 2. A brief s u m m a r y o f w o r k to b e p e r f o r m e d during the n e x t year o f support if c h a n g e d from the original proposal; a n indication o f a n y current p r o b l e m s or favorable or u n u s u a l d e v e l o p m e n t s, a n d a n y other significant i n f o r m a t i o n pertinent to the type o f project supported b y N S F or as specified b y the t e r m s a n d c o n d i t i o n s o f the grant; 3. S t a t e m e n t o f funds e s t i m a t e d to r e m a i n unobligated i f m o r e than 2 0 % at the e n d o f the p e n o d for w h i c h N S F currently is p r o v i d i n g support, 4. P r o p o s e d b u d g e t for the e n s u i n g year in the N S F format, o n l y if the original a w a r d letter did not indicate specific incremental a m o u n t s or if a d j u s t m e n t s to a p l a n n e d i n c r e m e n t e x c e e d i n g the greater o f 1 0 % or $ 1 0, are b e i n g requested, 5. Information about other current a n d p e n d i n g research support o f senior p e r s o n n e l, if c h a n g e d from the p r e v i o u s s u b m i s s i o n ; 6. A statement describing any contribution o f the project to the area o f e d u c a t i o n a n d h u m a n - r e s o u r c e d e v e l o p m e n t, if c h a n g e d from any p r e v i o u s s u b m i s s i o n, a n d 7. U p d a t e d information on a n i m a l care a n d use, Institutional B i o h a z a r d C o m m i t t e e a n d H u m a n Subject Certification, if c h a n g e d substantially from those originally p r o p o s e d a n d approved. 1. S e e a t t a c h m e n t s. 2. S e e a t t a c h m e n t s. 3. A l l f u n d s a l l o c a t e d f o r t h e p e r i o d 9 / / 9 7 w i l l b e s p e n t b y 8 / 3 1 / T h e r e q u e s t e d b u d g e t f o r t h e p e r i o d 9 / / 9 8 i s $ 1 4 2, 0 0 0, t h e a m o u n t s p e c i f i e d i n t h e o r i g i n a l a w a r d l e t t e r. 5. S e e a t t a c h m e n t s. 6. S e e a t t a c h m e n t s. 7. N o t a p p l i c a b l e. I certify' that to the best o f m y k n o w l e d g e ( 1 ) the statements herein ( e x c l u d i n g scientific h y p o t h e s e s a n d scientific o p i n i o n s ) are true a n d c o m p l e t e, a n d (2) the text a n d graphics in this report as w e l l as a n y a c c o m p a n y i n g publications or other d o c u m e n t s, u n l e s s o t h e r w i s e indicated, are the original w o r k o f the signatories or individuals w o r k i n g u n d e r their supervision. I u n d e r s t a n d that the willful provision o f false information or c o n c e a l i n g a material fact in this report or a n y other c o m m u n i c a tion s u b m i t t e d to N S F is a criminal offense ( U. S. C o d e, Title 18, S e c t i o n ) PI Signature:. N S F F o r m ( 7 / 9 5 )

22 Progress During the Past Year Our experiments designed to assess the stability of the CH 3 S0 2 radical were discussed in detail in our last annual report. During the past year some time was spent bringing our studies of the CH 3 + S0 2 + M reaction to completion. We find that the room temperature rate coefficient is 3.4 x cm 3 molecule 1 s" 1, nearly an order of magnitude smaller than the values reported by Calvert et al. [in Chemical Reactions in the Urban Atmosphere (1971)] and James et al.[j.c.s. Far. Trans. I, 2124 (1973)]. We also observe a rather large negative activation energy for the rate coefficient, suggesting the possibility that the reaction mechanism may be more complex than a simple addition of the carbon atom of the methyl to the sulfur atom on S0 2. We find the rate coefficient to be pressure dependent over the range of Torr, which is contrary to the findings of James et al.[(1973)] who report the rate coefficient to be independent of pressure over the range Torr. Finally, despite our best efforts, we have not been able to observe evidence for CH 3 S0 2 decomposition, i.e., regeneration of CH 3 on the millisecond experimental time scale. Over the past year a considerable amount of effort has been expended studying the kinetics and mechanism of the OH + DMSO reaction. Dimethyl sulfoxide, (DMSO, CH 3 S(0)SH 3 ), is an intermediate in the OH-initiated atmospheric oxidation of DMS. DMSO has been measured in the atmosphere [e.g. Harvey and Lang, Geophys. Res. Lett. 13, 49 (1986); Berreshiem et al., J. Geophys. Res. 98, (1993); Bandy et al.,geophys. Res. Lett. 23, 741 (1996)] and has been observed in laboratory chamber studies examining the OH-initiated oxidation of DMS [Barnes et al., Geophys. Res. Lett. 21, 2389, (1994), Sorensen et al., J. Atmos. Chem. 24, 299 (1996)]. Two previous studies exploring the OH + DMSO reaction indicate the reaction is very fast and suggest that it proceeds via OH addition to the S atom, forming an adduct [Barnes et al., in Biogenic sulfur in the Environment (1989); Hynes and Wine, J. Atmos. Chem. 24, 23 (1996)]. In the experiments conducted by Hynes and Wine [1996], the temporal profile of OH was monitored via laser induced fluorescence. Unlike the OH + DMS reaction, the rate coefficient of the OH + DMSO reaction was not observed to exhibit a kinetic isotope effect when deuterated DMSO was used, indicating that H-abstraction was not an important reaction pathway. Further,

23 the adduct formed by the OH + DMSO reaction was not observed to dissociate back to reactants. Based on numerous laboratory chamber studies and the study of Hynes and Wine [1996] the following reaction pathways may be considered viable: (1) OH + CH 3 S(0)CH 3 CH 3 S(OH)(0)CH 3 (a) CH 3 S(OH)(0)CH 3 + M -» CH 3 + CH 3 S(OH)(0) + M (b) CH 3 S(OH)(0)CH 3 + M CH 3 + CH 4 + S0 2 + M ( c ) CH 3 S(OH)(0)CH > CH 3 S(0) 2 CH 3 + H0 2 (d) CH 3 S(OH)(0)CH other products, CH 4, S0 2,? We have combined time-resolved tunable diode laser spectroscopic detection of CH 3 radicals at cm" 1 with 248 nm laser flash photolysis of H /DMSO/N 2 /CH 4 mixtures to measure the rate coefficient and CH 3 yield from the OH + DMSO reaction in the absence of oxygen, i.e. channel (a). At room temperature and 30 Torr total pressure, reaction (1) proceeds via an addition-elimination mechanism, generating methyl radicals in unit yield. From the time resolved observations of methyl appearance, we find that the lifetime of the DMSO-OH adduct toward methyl elimination is less than 10 LIS and the OH + DMSO rate coefficient is 8.8 x cm 3 molecule" 1 s 1 (in good agreement with earlier studies which employed time-resolved detection of OH disappearance [Hynes and Wine (1996)] or competitive kinetic techniques [Barnes et al.,(1989)]). To further elucidate the OH + DMSO reaction mechanism, we have also employed tunable diode laser absorption spectroscopy (TDLAS) in an attempt to detect CH 4 production in both the absence and presence of 0 2 (channels (b) and (d)). The CH 3 + HBr reaction produces CH 4 in unit yield and was used to calibrate the CH 4 infrared absorption signal at cm 1. At room temperature and 20 Torr total pressure, CH 4 was not observed as a product of the OH + DMSO

24 reaction in either N 2 or 0 2 buffer gas. Based on the infrared signal calibration, upper limits on the CH 4 yields derived from the data are (95% confidence limit) in N 2 buffer gas and in 0 2 buffer gas. Our studies of the OH + DMSO reaction demonstrate that this reaction proceeds rapidly and, in the absence of 0 2, produces CH 3 radicals in unit yield. Methane is not produced in either the presence br absence of 0 2, suggesting the remaining product is likely methane sulfinic acid, i.e., CH 3 S(0)OH. Because CH 3 reacts rapidly with 0 2, detection of CH 3 from OH + DMSO in 0 2 buffer is not feasible. It is possible that in the presence of sufficient 0 2 the DMSO-OH adduct will react with 0 2, producing H0 2 and DMS0 2 (CH 3 S(0) 2 CH 3 ) prior to methyl elimination. However, recent field measurements of DMSO and DMS0 2 indicate that the conversion of DMSO to DMS0 2 from the OH + DMSO reaction is highly inefficient under atmospheric conditions [Bandy et al. (1996)]. We are currently completing experiments which utilize TDLAS in an attempt to detect CH 4 production from the reaction of DMS + OH in the presence of oxygen. The OH initiated oxidation of DMS proceeds via 0 2 -dependent and 0 2 -independent pathways. The oxygen dependent pathway involves the formation of an adduct, DMS-OH, which reacts with 0 2 producing DMSO and H0 2 with a yield of approximately 50% [Hynes et al., in Dimethylsulfide: Oceans. Atmosphere, and Climate (1993); Turnipseed et al., J. Phys. Chem. 100, (1996)]. The identity of the remaining products is presently unknown. With the completion of our TDLAS studies designed to detect CH 4, we anticipate to, at the very minimum, narrow the list of potential products from the DMS-OH reaction. Another research track we have pursued during the past year has involved construction of an apparatus which couples laser flash photolysis (LFP) with time-resolved detection of reactants and products by photoionization mass spectrometry (PIMS). As mentioned in our last annual report, work on development of the LFP-PLMS apparatus stopped for a period of time because the student who was working on this project decided to drop back from the Ph.D. program to the Masters program and, as a result, switched to a shorter term project. Last autumn, Rafal

25 Strekowski, a Ph.D. student in the Georgia Tech School of Earth and Atmospheric Sciences, began working on the LFP-PLMS experiment as his dissertation project. We hope to detect ions for the first time this summer, and to begin getting data on CH 3 SO x reactions by this autumn. Publications Acknowledging NSF Support, 1/95-present 1. Quantum yield for carbon monoxide production in the 248 nm photodissociation of carbonyl sulfide (OCS), Z. Zhao, R. E. Stickel, and P. H. Wine, Geophys. Res. Lett. 2 2, 615 (1995). 2. Kinetics of reactions of atomic chlorine with H 2 S, D 2 S, CH 3 SH, and CD 3 SD, J. M. Nicovich, S. Wang, and P. H. Wine, Int. J. Chem. Kinet. 22, 359 (1995). 3. Sulfur in the atmosphere, H. Berresheim, P. H. Wine, and D. D. Davis, in Composition. Chemistry, and Climate of the Atmosphere, ed. By H. B. Singh, Van Nostrand Reinhold, pp (1995). 4. A mechanistic study of the reaction of OH with dimethyl-d 6 sulfide. Direct observation of adduct formation and the kinetics of the adduct reaction with 0 2, A. J. Hynes, R. B. Stroker, A. J. Pounds, T. McKay, J. D. Bradshaw, J. M. Nicovich, and P. H. Wine, J. Phys. Chem. 2 9., (1995). 5. Branching ratios for methyl elimination in the reactions of OD radicals and CI atoms with CH 3 SCH 3, Z. Zhao, R. E. Stickel, and P. H. Wine, Chem. Phys. Lett , 59 (1996). 6. The atmospheric chemistry of dimethyl sulfoxide (DMSO). Kinetics and mechanism of the OH + DMSO reaction, A. J. Hynes and P. H. Wine, J. Atmos. Chem. 2 4, 23 (1996). 7. Laboratory studies of atmospheric sulfur chemistry using tunable diode laser probes, R. E. Stickel, S. P. Urbanski, Z. Zhao, and P. H. Wine, in Application of Tunable Diode and Other Infrared Sources for Atmospheric Studies and Industrial Process Monitoring (ed. by A. Fried), SPIE Volume 2834, pp , Mechanistic and kinetic study of formaldehyde production in the atmospheric oxidation of dimethyl sulfide, S. P. Urbanski, R. E. Stickel, Z. Zhao, and P. H. Wine, J. Chem. Soc. Farad. Trans., in press.

26 Reprints of publications 1-5 have been submitted with previous annual reports, of publications 6 and 7 are enclosed. Two reprints each Plans for the Upcoming Year During the upcoming year, we plan to continue to pursue several lines of research relating to atmospheric sulfur chemistry. These include the following: 1. We will complete our mechanistic study of the OH -I- DMSO reaction by using the tunable diode laser absorption spectroscopy (TDLAS) technique to measure S0 2 yields in both the presence and absence of We will begin to explore the atmospheric chemistry of methane sulfuric acid, CH 3 S(0)OH, which appears to be an important product of the OH + DMSO reaction. Initial experiments will explore potential difficulties with handling gaseous samples of this species, which we expect to have a very low vapor pressure. 3. We will continue to work on development of LFP-PIMS technique with the longrange goal of applying this approach to kinetic and mechanistic studies of large organo-sulfur radicals. 4. We will initiate a study of the kinetics of the CH H0 2 reaction. The experimental approach will couple radical production by laser flash photolysis with simultaneous detection of CH and H0 2 using a combination of UV and IR time-resolved absorption techniques. 5. We plan to initiate a series of LFP-PLIF (pulsed laser induced fluorescence) experiments to investigate several aspects of atmospheric sulfur chemistry. Two of the higher priority experiments include measurement of the yield of SO from the CS 2 OH reaction and investigation of the atmospheric chemistry of thioformaldehyde (H 2 CS). A recent smog chamber study by Barnes et al. [Geophys. Res. Lett. 21, 2389 (1994)] suggests that H 2 CS may be an important intermediate in DMS oxidation. We will investigate the slow CH 3 S reaction as a possible source of H 2 CS, as well as the mechanism for conversion of H 2 CS to the more stable