Progress 10/01/07 to 09/30/12
Outputs
OUTPUTS: Three major objectives of this project were: (a) to carry out laboratory studies of the kinetics and products of the gas-phase reactions of selected volatile "model" organophosphorus and organosulfur compounds, (b) to carry out laboratory studies of the atmospherically relevant reactions of polycyclic aromatic hydrocarbons and other volatile organic compounds (VOCs), and (c) to continue ongoing reviews and evaluations of kinetic and mechanistic literature data as part of an International Union of Pure and Applied Chemistry (IUPAC) data evaluation panel, with an expansion into the development of structure-reactivity relationships which will aid in the formulation of detailed chemical mechanisms for atmospheric photooxidations of VOCs. The atmospheric chemistry of the organophosphorus compounds isopropyl methyl methylphosphonate, dimethyl N,N-dimethylphosphoroamidate, and dichlorvos (the latter an in-use pesticide) and of the organosulfur compounds divinyl sulfoxide, 1,4-thioxane and 1,4-dithiane were studied. Daytime reaction with hydroxyl (OH) radicals was calculated to be the dominant chemical atmospheric loss process for all of these compounds. Products of the OH radical-initiated reactions were investigated, and rate constants for the OH radical reactions were measured over the range 280-350 K. The OH radical reaction rate constants all increase with decreasing temperature, showing that the reactions proceed by formation of an intermediate complex which decomposes back to reactants in competition with decomposition to the observed products. Experimental studies of selected atmospherically-relevant reactions of a number of VOCs and semi-volatile organic compounds, including a series of 1-alkenes and 2-methyl-1-alkenes, diethylamine (a chemical emitted from animal husbandry operations and implicated in secondary organic aerosol formation), the polycyclic aromatic hydrocarbons naphthalene, 1,7-, 2,7- and 1,6-dimethylnaphthalene and triphenylene (emitted from incomplete combustion of fossil fuels), 2-formylcinnamaldehyde (a major product of the OH radical-initiated reaction of naphthalene), 1,4-butanediol, and diethyl phosphate (a first-generation product of the reaction of OH radicals with triethyl phosphate) were also carried out. Alkoxy radicals are key intermediates in the atmospheric degradations of VOCs, and can typically undergo reaction with O2, unimolecular decomposition or unimolecular isomerization. Previous structure-reactivity relationships for the estimation of rate constants for these processes were updated to incorporate recent kinetic data from absolute and relative rate studies. Temperature-dependent rate expressions were derived, allowing rate constants for all three of these alkoxy radical reaction pathways to be calculated at atmospherically relevant temperatures. New datasheets dealing with the atmospheric reactions of benzene, toluene, several ring-retaining products of benzene and toluene, and of the 4-carbon alkanes and alkenes isobutane, 1-butene, isobutene and cis- and trans-2-butene were prepared and added to the IUPAC atmospheric chemistry website. PARTICIPANTS: Dr. Ernesto C. Tuazon, University of California, Riverside. Prof. Janet Arey, University of California, Riverside. Ms. Sara M. Aschmann, University of California, Riverside. Dr. Sherri A. Mason, State Univeresity of New York, Fredonia, NY. Dr. Lin Wang, University of California, Riverside. Dr. Noriko Nishino, University of California, Riverside. Dr. Kathryn Zimmermann, University of California, Riverside. TARGET AUDIENCES: The data obtained in this project will be used by the atmospheric science community and by federal and state regulators. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.
Impacts
This project has resulted in 15 peer-reviewed publications and a book chapter (see the list below) over the past 5 years and involved three graduate students and a visiting Associate Professor from the State University of New York at Fredonia on sabbatical leave. Among the outputs of this work, an estimation method for calculating the rate constants of the OH radical reactions with alkyl phosphates, alkyl phosphonates, alkyl phosphorothioates and alkyl phosphonothioates has been developed and published, and should be useful for estimating OH radical reaction rate constants for organophosphorus compounds which have not been studied experimentally. The reviews and evaluations of kinetic and mechanistic literature data as part of an International Union of Pure and Applied Chemistry (IUPAC) data evaluation panel, which are ongoing, are freely available on the world-wide web at http://www.iupac-kinetic.ch.cam.ac.uk
Publications
- Atkinson, R. 2007. Rate constants for the atmospheric reactions of alkoxy radicals: an updated estimation method. Atmos. Environ. 41: 8468-8485.
- Aschmann, S. M., Long, W. D. and Atkinson, R. 2008. Rate constants for the gas-phase reactions of OH radicals with dimethyl phosphonate over the temperature range 278-351 K and for a series of other organophosphorus compounds at 280 K. J. Phys. Chem. A 112: 4793-4799.
- Atkinson, R., Baulch, D. L., Cox, R. A., Crowley, J. N., Hampson, R. F., Hynes, R. G., Jenkin, M. E., Rossi, M. J., Troe, J. and Wallington, T. J. 2008. Evaluated kinetic and photochemical data for atmospheric chemistry: volume IV - gas phase reactions of organic halogen species. Atmos. Chem. Phys. 8: 4141-4496.
- Aschmann, S. M., Tuazon, E. C., Long, W. D. and Atkinson, R. 2008. Kinetics and products of the gas-phase reactions of divinyl sulfoxide with OH and NO3 radicals and O3. J. Phys. Chem. A 112: 8723-8730.
- Atkinson, R. 2008. Our present understanding of the gas phase atmospheric degradation of VOCs, in Simulation and Assessment of Chemical Processes in a Multiphase Environment, Eds. I. Barnes and M. M. Kharytonov, NATO Sciences for Peace and Security Series - C: Environmental Security, Springer, Dordrecht, the Netherlands, pp. 1-19.
- Aschmann, S. M., Long, W. D. and Atkinson, R. 2008. Kinetics of the gas-phase reactions of OH and NO3 radicals and O3 with 1,4-thioxane and 1,4-dithiane. J. Phys. Chem. A 112: 13556-13565.
- Mason, S. A., Arey, J. and Atkinson, R., 2009. Rate Constants for the Gas-Phase Reactions of NO3 Radicals and O3 with C6-C14 1-Alkenes and 2-Methyl-1-alkenes at 296 2 K. J. Phys. Chem. A, 113: 5649-5656.
- Nishino, N., Arey, J. and Atkinson, R. 2009. Formation and reactions of 2-formylcinnamaldehyde in the OH radical-initiated reaction of naphthalene. Environ. Sci. Technol. 43: 1349-1353.
- Wang, L., Aschmann, S. M., Atkinson, R. and Arey, J. 2009. Effect of NO2 concentration on product yields of the gas-phase NO3 radical-initiated reactions of ethyl- and dimethyl-naphthalenes. Environ. Sci. Technol. 43: 2766-2772.
- Mason, S. A., Arey, J. and Atkinson, R. 2010. Kinetics and products of the OH radical-initiated reaction of 1,4-butanediol and rate constants for the reactions of OH radicals with 4-hydroxybutanal and 3-hydroxypropanal. Environ. Sci. Technol.: 44: 707-713.
- Aschmann, S. M.; Tuazon, E. C., Long, W. D. and Atkinson, R. 2010. Atmospheric chemistry of isopropyl methyl methylphosphonate and dimethyl N,N-dimethylphosphoroamidate. J. Phys. Chem. A: 114, 3523-3532.
- Aschmann, S. M., Tuazon, E. C., Long, W. D. and Atkinson, R., 2011. Atmospheric chemistry of dichlorvos. J. Phys. Chem. A: 115, 2756-2764.
- Tuazon, E. C., Martin, P., Aschmann, S. M., Arey, J. and Atkinson, R., 2011. Kinetics of the reactions of OH radicals with 2-methoxy-6-(trifluoromethyl)pyridine, diethylamine, and 1,1,3,3,3-pentamethyldisiloxan-1-ol at 298 2 K. Int. J. Chem. Kinet.: 43, 631-638.
- Zimmermann, K., Atkinson, R., Arey, J., Kojima, Y. and Inazu, K., 2012. Isomer distribution of molecular weight 247 and 273 nitro-PAHs in ambient samples, NIST diesel SRM, and from chamber radical-initiated reactions. Atmos. Environ.: 55, 431-439.
- Zimmermann, K., Atkinson, R. and Arey, J., 2012. Effect of NO2 concentration on dimethylnitronaphthalene yields and isomer distribution patterns from the gas-phase OH radical-initiated reactions of selected dimethylnaphthalenes. Environ. Sci. Technol.: 46, 7535-7542.
- Nishino, N., Arey, J. and Atkinson, R., 2012. 2-Formylcinnamaldehyde formation yield from the OH radical-initiated reaction of naphthalene: effect of NO2 concentration. Environ. Sci. Technol.: 46, 8198-8204.
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Progress 01/01/11 to 12/31/11
Outputs
OUTPUTS: During 2011, two projects were completed. Reaction rate constants for the gas-phase reactions of 2-methoxy-6-(trifluoromethyl)pyridine and diethylamine with hydroxyl radicals were measured, allowing the atmospheric lifetimes of these two VOCs with respect to reaction with OH radicals to be calculated. 2-Methoxy-6-(trifluoromethyl)pyridine has been proposed as a crop protection chemical in Europe, and diethylamine (and other amines) is emitted into the atmosphere from animal manure. The lifetimes of the VOCs studied here with respect to reaction with hydroxyl radicals are calculated to be 7.5 days for 2-methoxy-6-(trifluoromethyl)pyridine and 1.2 hr for diethylamine. We showed that 2-methoxy-6-(trifluoromethyl)pyridine does not react with gaseous nitric acid or ozone, and since photolysis and reaction with nitrate radicals are also expected to be of no importance, its calculated lifetimes with respect to reaction with hydroxyl radicals will be the overall atmospheric lifetime due to chemical loss processes. However, diethylamine will also react with gaseous nitric acid (to form the nitrate salt), reacts slowly with ozone, and is expected to react with nitrate radicals. While its reaction with ozone is of no importance in the atmosphere, the calculated lifetime of diethylamine with respect to reaction with hydroxyl radicals during daylight hours will be an upper limit to the daytime lifetime of diethylamine, with additional chemical removal during daytime and nighttime due to reaction with nitric acid and with nighttime removal by reaction with nitrate radicals also occurring. Molecular weight (mw) 247 nitrofluoranthenes and nitropyrenes and mw 273 nitrotriphenylenes, nitrobenz[a]anthracenes, and nitrochrysenes have quantified in ambient particles collected in Riverside, CA, Tokyo, Japan, and Mexico City, Mexico. 2-Nitrofluoranthene was the most abundant nitrated polycyclic aromatic hydrocarbon (nitro-PAH) in Riverside and Mexico City, and the mw 273 nitro-PAHs were observed in lower concentrations. However, in Tokyo concentrations of 1- + 2-nitrotriphenylene were more similar to that of 2-nitrofluoranthene. The atmospheric formation pathways of nitro-PAHs were studied from environmental chamber reactions of fluoranthene, pyrene, triphenylene, benz[a]anthracene, and chrysene with hydroxyl and nitrate radicals at room temperature and atmospheric pressure. Sampling media were spiked with deuterated PAH to examine heterogeneous nitration. Comparing specific nitro-PAH ratios in ambient and diesel particles with the nitro-PAH profiles from our chamber data suggests that the low 2-nitrofluoranthene/nitrotriphenylenes ratios in Tokyo particulate matter are not a result of gas-phase radical-initiated chemistry. Heterogeneous formation of deuterated nitro-PAHs on the sampling media suggest that heterogeneous reactions with dinitrogen pentaoxide (which is in equilibrium with nitrate radicals and nitrogen dioxide) on ambient particle surfaces also do not explain the nitro-PAH profiles of Tokyo particles. Thus, the source of nitrotriphenylenes in Tokyo remains unidentified. PARTICIPANTS: Sara M. Aschmann and William D. long, Staff Research Associates. Ernesto C. Tuazon, Research Professor Emeritus. Kathryn Zimmermann, Gradi=uate student at UC Riverside. Janet Arey, Professor, UC Riverside TARGET AUDIENCES: Atmospheric sciences research community and regulatory agencies. PROJECT MODIFICATIONS: Not relevant to this project.
Impacts
The dominant atmospheric reaction of the organophosphorus and organosulfur compounds studied to date in this project is by reaction with the OH radical. The rate constants for these reactions all increase with decreasing temperature, showing that the reactions proceed by formation of an intermediate complex which decomposes back to reactants in competition with decomposition to the observed products. For the organophosphorus compounds involved, the major products observed involves replacement of one of the RO groups (R = alkyl) by an HO group and with the phosphorothioates also reacting to a significant extent to convert the P=S group by a P=O group (i.e., forming the oxon). An estimation method for calculating the rate constants of the OH radical reactions with alkyl phosphates, alkyl phosphonates, alkyl phosphorothioates and alkyl phosphonothioates has been developed and published, and should be useful for estimating OH radical reaction rate constants for organophosphorus compoudns which have not been studied experimentally. The work on reactions of other volatile organic compounds will be used by chemical modelers for input into models which are used to predict urban and regional ozone and secondary particle formation.
Publications
- Aschmann, S. M., Tuazon, E. C., Long, W. D., Atkinson, R., 2011. Atmospheric chemistry of dichlorvos. J. Phys. Chem. A: 115, 2756-2764.
- Tuazon, E. C., Martin, P., Aschmann, S. M., Arey, J., Atkinson, R., 2011. Kinetics of the Reactions of OH Radicals with 2-Methoxy-6-(trifluoromethyl)pyridine, Diethylamine, and 1,1,3,3,3-Pentamethyldisiloxan-1-ol at 298 +/- 2 K. Int. J. Chem. Kinet.: 43, 631-638.
- Zimmermann, K., Atkinson, R., Arey, J., Kojima, Y., Inazu, K., 2012. Isomer Distribution of Molecular Weight 2147 and 273 Nitro-PAHs in Ambient Samples, NIST Diesel SRM, and from Chamber Radical-Initiated Reactions. Atmos. Environ., submitted for publication.
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Progress 01/01/10 to 12/31/10
Outputs
OUTPUTS: During 2010, kinetic and product studies of the atmospherically-relevant reactions of the in-use insecticide dichlorvos (2,2-dichlorovinyl dimethyl phosphate) have been carried out. As for other organophosphorus compounds previously studied, rate constants for their reactions with hydroxyl (OH) radicals, nitrate (NO3) radicals and ozone (O3) have been measured at room temperature, and rate constants for the OH radical reactions with measured over the temperature range 296-350 K. Products of the OH radical reaction have been investigated using in situ Fourier transform infrared spectroscopy and direct air sampling atmospheric pressure ionization tandem mass spectrometry, and aerosol formation measured. The major products observed and quantified were phosgene and dimethyl phosphate. Our work shows that gaseous dichlorvos will be transformed in the atmosphere during both daytime and nighttime within typically a few hours, leading to the formation of phosgene [C(O)Cl2] and dimethyl phosphate [(CH3O)2P(O)OH] as major products and with little aerosol formation. A manuscript reporting the results of the work is currently in-press in the Journal of Physical Chemistry A. Experiments have also been carried out to measure the rate constant for the reaction of hydroxyl radicals with diethylamine, a chemical emitted from animal husbandry operations and implicated in secondary organic aerosol formation. Diethylamine is also a high-volume chemical used as a solvent, a corrosion inhibitor and as an intermediate in the manufacture of other chemicals. Experiments were carried out using in situ Fourier transform infrared spectroscopy for analysis and hydroxyl radicals were generated from the dark reaction of ozone with an alkene in order to avoid formation of nitric acid, which reacts with amines to form their nitrate salts. This is the first reported measurement of the rate constant for this reaction, which is expected to dominate as a diethylamine loss process in the atmosphere and hence determine diethylamines atmospheric lifetime. The calculated diethylamine lifetime due to reaction with OH radicals is approximately 1 hour during daylight hours. PARTICIPANTS: Sara M. Aschmann and William D. Long (SRAs at the Air Pollution Research Center, University of California, Riverside (UCR)) and Dr. Ernesto C. Tuazon (Research Professor, Emeritus at UCR) carried out the experimental work on the organophosphorus compounds and diethylamine. Dr. Sherri A. Mason, who carried out the experimental work on the kinetics of NO3 radicals and O3 with alkenes, is on the faculty at SUNY Fredonia who was on sabbatical at the Air Pollution Research Center, UCR, during 2009-2010 to gain knowledge and experience in conducting kinetic and products studies utilizing large-volume environmental chambers. Dr. Janet Arey is a faculty member at UCR. TARGET AUDIENCES: The target audiences for this research are the atmospheric science research community and scientists at regulatory agencies and in industry. This audience is reached by publication of this research in peer-reviewed journal articles. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.
Impacts
The research carried out in 2010, when combined with previous years work on other volatile "model" organophosphorus compounds, shows that the dominant atmospheric reaction of the organophosphorus compounds studied to date is reaction with the OH radical, with dichlorvos, which contains a -CH=CCl2 moiety, also reacting with NO3 radicals. The rate constants for these reactions all increase with decreasing temperature, showing that the reactions proceed by formation of an intermediate complex which decomposes back to reactants in competition with decomposition to the observed products. For the organophosphorus compounds involved, the major products observed involves replacement of one of the RO groups (R = alkyl) by an HO group and with the phosphorothioates also reacting to a significant extent to convert the P=S group by a P=O group (i.e., forming the oxon). An estimation method for calculating the rate constants of the OH radical reactions with alkyl phosphates, alkyl phosphonates, alkyl phosphorothioates and alkyl phosphonothioates has been developed and published, and should be useful for estimating OH radical reaction rate constants for organophosphorus compoudns which have not been studied experimentally. The kinetic research on diethylamine, emitted from animal husbandary operations, advances our knowledge of the rates of reaction of alkylamines (and hance of their atmospehric lifetimes) and provides important information concerning the reaction mechanisms and the reaction products formed.
Publications
- Mason, S. A., Arey, J., Atkinson, R., 2009. Rate constants for the gas-phase reactions of NO3 radicals and O3 with C6-C14 1-alkenes and 2-methyl-1-alkenes at 296 2 K. J. Phys. Chem. A, 113: 5649-5656.
- Aschmann, S. M.; Tuazon, E. C., Long, W. D. and Atkinson, R. 2010. Atmospheric chemistry of isopropyl methyl methylphosphonate and dimethyl N,N-dimethylphosphoroamidate. J. Phys. Chem. A: 114, 3523-3532.
- Aschmann, S. M., Tuazon, E. C., Long, W. D., Atkinson, R., 2011. Atmospheric chemistry of dichlorvos. J. Phys. Chem. A: in press.
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Progress 01/01/09 to 12/31/09
Outputs
OUTPUTS: There are two bjectives of this project: (a) to carry out laboratory studies of the kinetics and products of the gas-phase reactions of selected volatile "model" organophosphorus compounds, including the investigation of the lifetimes and fates of first-generation phosphorus-containing reaction products, and (b) to continue ongoing reviews and evaluations of kinetic and mechanistic literature data as part of an International Union of Pure and Applied Chemistry (IUPAC) data evaluation panel. During 2009, kinetic and product studies of the atmospherically-relevant reactions of isopropyl methyl methylphosphonate, dimethyl N,N-dimethylphosphoroamidate, and dichlorvos have been carried out. Rate constants for their reactions with OH and NO3 radicals and O3 have been measured at room temperature, and rate constants for the OH radical reactions with isopropyl methyl methylphosphonate and dimethyl N,N-dimethylphosphoroamidate have been measured over the temperature range 280-350 K. Products of the OH radical reactions with isopropyl methyl methylphosphonate and dimethyl N,N-dimethylphosphoroamidate have been investigated using gas chromatography, in situ Fourier transform infrared spectroscopy and direct air sampling atmospheric pressure ionization tandem mass spectrometry, and aerosol formation measured. A structure-reactivity relationship allowing the calculation of OH radical reaction rate constants with alkyl phoshates, alkyl phosphonates, alkyl phosphorothioates and alkyl phosphonothioates has been developed and is included in our publication on isopropyl methyl methylphosphonate and dimethyl N,N-dimethylphosphoroamidate. An investigation of the reactions of first-generation products from OH + triethyl phosphate and diethyl methylphosphonate has commenced. The products, (CH3O)2P(O)OH from triethyl phosphate and (CH3O)P(O)(CH3)OH from diethyl methylphosphonate, were generated in situ in the chamber and their time-concentration profiles monitored by in situ atmospheric pressure ionization mass spectrometry (API-MS). From the time behavior, rate constant ratios k(OH + product)/k(OH + reactant) can be obtained. While this study is in its initial stages, the data obtained to date indicates that the products (CH3O)2P(O)OH and (CH3O)P(O)(CH3)OH are significantly more reactive towards OH radicals than are triethyl phosphate or diethyl methylphosphonate, by a factor of 2 or more. Furthermore, wall losses of (CH3O)2P(O)OH and (CH3O)P(O)(CH3)OH were relatively minor, suggesting that these product species will react rapidly in the gas phase, with lifetimes of about an hour or less during daylight hours. The API-MS spectra suggest that the products of OH + (CH3O)2P(O)OH and OH + (CH3O)P(O)(CH3)OH are CH3OP(O)(OH)2 and CH3P(O)(OH)2, respectively. Further work on these and related reactions will be continued. New review and evaluation datasheets dealing with the atmospheric chemistry of the 4-carbon alkanes and alkenes isobutane, 1-butene, isobutene and cis- and trans-2-butene have been prepared and are now available on the IUPAC atmospheric chemistry website. PARTICIPANTS: The following individuals worked on this project: Roger Atkinson (PI), Janet Arey (Professor) Ernesto C. Tuazon (Research Chemist), Sara M. Aschmann and William D. Long (Staff Research Associates), and Lin Wang and Noriko Nishino (graduate students). The studies of the atmospheric chemsitry of volatile organic compounds carried out by Lin Wang and Noriko Nishino was part of their Ph.D. theses, and contributed to their graduate teaching and experience. TARGET AUDIENCES: The atmospheric chemistry community and scientists involved with usage and regulation of organophosphorus pesticides. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.
Impacts
The dominant atmospheric reaction of the organophosphorus and organosulfur compounds studied to date is by reaction with the OH radical. The rate constants for these reactions all increase with decreasing temperature, showing that the reactions proceed by formation of an intermediate complex which decomposes back to reactants in competition with decomposition to the observed products. For the organophosphorus compounds involved, the major products observed involves replacement of one of the RO groups (R = alkyl) by an HO group and with the phosphorothioates also reacting to a significant extent to convert the P=S group by a P=O group (i.e., forming the oxon). An estimation method for calculating the rate constants of the OH radical reactions with alkyl phosphates, alkyl phosphonates, alkyl phosphorothioates and alkyl phosphonothioates has been developed and published, and should be useful for estimating OH radical reaction rate constants for organophosphorus compoudns which have not been studied experimentally. The estimation method developed here for the atmospheric reactions of alkoxy radicals is being implemented into the University of Leeds, UK, Master Chemical Mechanism, which is widely used for atmospheric chemical modeling. Similarly, through the PI's membership on the IUPAC subcommittee on data evaluation for atmospheric chemistry, the continual evaluation and review of kinetic and mechanistic data for chemical reactions important in the atmosphere allows up-to-date recommendations to be available to chemical modelers for input into models which are used to predict urban and regional ozone and secondary particle formation.
Publications
- Nishino, N., Arey, J. and Atkinson, R. 2009. Formation and reactions of 2-formylcinnamaldehyde in the OH radical-initiated reaction of naphthalene. Environ. Sci. Technol. 43: 1349-1353.
- Wang, L., Aschmann, S. M., Atkinson, R. and Arey, J. 2009. Effect of NO2 concentration on product yields of the gas-phase NO3 radical-initiated reactions of ethyl- and dimethyl-naphthalenes. Environ. Sci. Technol. 43: 2766-2772.
- Mason, S. A., Arey, J. and Atkinson, R. 2010. Kinetics and products of the OH radical-initiated reaction of 1,4-butanediol and rate constants for the reactions of OH radicals with 4-hydroxybutanal and 3-hydroxypropanal. Environ. Sci. Technol., 44: 707-713.
- Aschmann, S. M.; Tuazon, E. C., Long, W. D. and Atkinson, R. 2010. Atmospheric chemistry of isopropyl methyl methylphosphonate and dimethyl N,N-dimethylphosphoroamidate. J. Phys. Chem. A: in press.
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Progress 01/01/08 to 12/31/08
Outputs
OUTPUTS: There are two major objectives of this project: (a) to carry out laboratory studies of the kinetics and products of the gas-phase reactions of selected volatile "model" organophosphorus compounds, including the investigation of the lifetimes and fates of first-generation phosphorus-containing reaction products, and (b) to continue ongoing reviews and evaluations of kinetic and mechanistic literature data as part of an International Union of Pure and Applied Chemistry (IUPAC) data evaluation panel, with an expansion into the development of structure-reactivity relationships which will aid in the formulation of detailed chemical mechanisms for atmospheric photooxidations of volatile organic compounds (VOCs). During 2008, kinetic and product studies of the atmospherically-relevant reactions of the organosulfur compounds divinyl sulfoxide, 1,4-thioxane and 1,4-dithiane have been carried out. Rate constants for their reactions with NO3 radicals and O3 were measured at room temperature, and rate constants for their reactions with OH radicals were measured over the temperature range ~280-350 K. Products of the OH radical-initiated reaction with divinyl sulfoxide were investigated using gas chromatography and in situ Fourier transform infrared spectroscopy, and aerosol formation has been measured from the OH radical-initiated reactions of these three organosulfur compounds. The atmospheric chemistry of the three organophosphorus compounds isopropyl methyl methylphosphonate, dimethyl N,N-dimethylphosphoroamidate, and dichlorvos (the latter an in-use pesticide) has been, or is being, studied. As for other organophosphorus and organosulfur compounds, rate constants for their reactions with OH and NO3 radicals and O3 have been measured at room temperature, and rate constants for the OH radical reactions with isopropyl methyl methylphosphonate and dimethyl N,N-dimethylphosphoroamidate have been measured over the temperature range 280-350 K. Products of the OH radical reactions with isopropyl methyl methylphosphonate and dimethyl N,N-dimethylphosphoroamidate have been investigated using gas chromatography, in situ Fourier transform infrared spectroscopy and direct air sampling atmospheric pressure ionization tandem mass spectrometry, and aerosol formation from the OH radical-initiated reactions has been measured. An additional publication from the on-going IUPAC data evaluation panel has appeared in the peer-reviewed on-line journal Atmospheric Chemistry and Physics. New review and evaluation datasheets dealing with the atmospheric chemistry of benzene and toluene and several of their ring-retaining products have been prepared and are now available on the IUPAC atmospheric chemistry website. The atmospheric chemistry of the 4-carbon alkanes and alkenes isobutane, 1-butene, isobutene and cis- and trans-2-butene will be dealt with in the near future. PARTICIPANTS: Not relevant to this project. TARGET AUDIENCES: Not relevant to this project. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.
Impacts
Reaction rates measured from our kinetic studies of the atmospherically relevant reactions of alkyl phosphates, phosphonates, phosphorothioates, phosphonothioates and phosphoroamidates can be used to predict the atmospheric lifetimes of these compounds. The dominant atmospheric reaction of the organophosphorus and organosulfur compounds studied to date is by reaction with the OH radical. The rate constants for these reactions all increase with decreasing temperature, showing that the reactions proceed by formation of an intermediate complex which decomposes back to reactants in competition with decomposition to the observed products. For the organophosphorus compounds involved, the major products observed involves replacement of one of the RO groups (R = alkyl) by an HO group and with the phosphorothioates also reacting to a significant extent to convert the P=S group by a P=O group (i.e., forming the oxon). The estimation method developed here for the atmospheric reactions of alkoxy radicals is being implemented into the University of Leeds, UK, Master Chemical Mechanism, which is widely used for atmospheric chemical modeling. Similarly, through the PI's membership on the IUPAC subcommittee on data evaluation for atmospheric chemistry, the continual evaluation and review of kinetic and mechanistic data for chemical reactions important in the atmosphere allows up-to-date recommendations to be available to chemical modelers for input into models which are used to predict urban and regional ozone and secondary particle formation.
Publications
- Aschmann, S. M., Long, W. D. and Atkinson, R. 2008. Rate constants for the gas-phase reactions of OH radicals with dimethyl phosphonate over the temperature range 278-351 K and for a series of other organophosphorus compounds at ~280 K. J. Phys. Chem. A 112: 4793-4799.
- Atkinson, R., Baulch, D. L., Cox, R. A., Crowley, J. N., Hampson, R. F., Hynes, R. G., Jenkin, M. E., Rossi, M. J., Troe, J. and Wallington, T. J. 2008. Evaluated kinetic and photochemical data for atmospheric chemistry: volume IV, gas phase reactions of organic halogen species. Atmos. Chem. Phys. 8: 4141-4496.
- Aschmann, S. M., Tuazon, E. C., Long, W. D. and Atkinson, R. 2008. Kinetics and products of the gas-phase reactions of divinyl sulfoxide with OH and NO3 radicals and O3. J. Phys. Chem. A 112: 8723-8730.
- Atkinson, R. 2008. Our present understanding of the gas phase atmospheric degradation of VOCs, in Simulation and Assessment of Chemical Processes in a Multiphase Environment, Eds. I. Barnes and M. M. Kharytonov, NATO Sciences for Peace and Security Series - C: Environmental Security, Springer, Dordrecht, the Netherlands, pp. 1-19.
- Aschmann, S. M., Long, W. D. and Atkinson, R. 2008. Kinetics of the gas-phase reactions of OH and NO3 radicals and O3 with 1,4-thioxane and 1,4-dithiane. J. Phys. Chem. A 112: 13556-13565.
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Progress 01/01/07 to 12/31/07
Outputs
There are two major objectives of this project: (a) to carry out laboratory studies of the kinetics and products of the gas-phase reactions of selected volatile "model" organophosphorus compounds, including the investigation of the lifetimes and fates of first-generation phosphorus-containing reaction products, and (b) to continue ongoing reviews and evaluations of kinetic and mechanistic literature data as part of an International Union of Pure and Applied Chemistry (IUPAC) data evaluation panel, with an expansion into the development of structure-reactivity relationships which will aid in the formulation of detailed chemical mechanisms for atmospheric photooxidations of volatile organic compounds (VOCs). During the first few months of this project, rate constants for the gas-phase reactions of OH radicals with dimethyl phosphonate, (CH3O)2P(O)H, have been measured over the temperature range 278-351 K. The temperature dependence of this reaction rate constant is
significantly less negative that we have previously measured for a series of other organophosphorus compounds (dimethyl methylphosphonate, dimethyl ethylphosphonate, diethyl methylphosphonate, diethyl ethylphosphonate and triethyl phosphate). For dimethyl methylphosphonate, dimethyl ethylphosphonate, diethyl methylphosphonate, diethyl ethylphosphonate and triethyl phosphate, experiments conducted at 278 K (a temperature below the local dew point where a water film was present on the outside of the Teflon reaction chamber) resulted in measured OH radical reaction rate constants which were significantly higher than expected from extrapolation of rate data obtained at temperatures above the local dew point (i.e., 293 K and above), suggesting the occurrence of a light-induced reaction at the wet chamber walls. Aerosol formation from the reactions of OH radicals with these organophosphorus compounds was found to be relatively minor, with aerosol yields of less than 8% in all cases. Alkoxy
radicals are key intermediates in the atmospheric degradations of volatile organic compounds, and can typically undergo reaction with O2, unimolecular decomposition or unimolecular isomerization. Previous structure-reactivity relationships for the estimation of rate constants for these processes for alkoxy radicals (Atkinson, International Journal of Chemical Kinetics, 29, 99-111, 1997; Aschmann and Atkinson, International Journal of Chemical Kinetics, 31, 501-513, 1999) have been updated to incorporate recent kinetic data from absolute and relative rate studies. Temperature-dependent rate expressions were derived allowing rate constants for all three of these alkoxy radical reaction pathways to be calculated at atmospherically relevant temperatures. An additional publication from the IUPAC data evaluation panel has appeared in Atmospheric Chemistry and Physics Discussions (a prelude to publication in the peer-reviewed journal Atmospheric Chemistry and Physics).
Impacts
Reaction rates measured from our kinetic studies of the atmospherically relevant reactions of alkyl phosphates, phosphonates, phosphorothioates and phosphonothioates can be used to predict the atmospheric lifetimes of these compounds. The estimation method developed here for the atmospheric reactions of alkoxy radicals is being implemented into the University of Leeds, UK, Master Chemical Mechanism, which is widely used for atmospheric chemical modeling. Similarly, through the PI's membership on the IUPAC subcommittee on data evaluation for atmospheric chemistry, the continual evaluation and review of kinetic and mechanistic data for chemical reactions important in the atmosphere allows up-to-date recommendations to be available to chemical modelers for input into models which are used to predict urban and regional ozone and secondary particle formation.
Publications
- Atkinson, R., Baulch, D. L., Cox, R. A., Crowley, J. N., Hampson, R. F., Hynes, R. G., Jenkin, M. E., Rossi, M. J., Troe, J. and Wallington, T. J. 2007. Evaluated kinetic and photochemical data for atmospheric chemistry: volume IV gas phase reactions of organic halogen species. Atmos. Chem. Phys. Discuss. 7: 16349-17067.
- Atkinson, R. 2007. Rate constants for the atmospheric reactions of alkoxy radicals: an updated estimation method. Atmos. Environ. 41: 8468-8485.
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