DMSO In The Atmosphere
RESEARCH INTERESTS
Overview of Research Program
Chemical change in the atmosphere is driven largely by reactions of photochemically generated free radicals. Sophisticated experimental techniques are required to quantitatively characterize important atmospheric photochemical processes as well as the kinetics and mechanisms of the fast free radical reactions that result. In our laboratory, laser flash photolysis and fast flow techniques are employed to generate reactive intermediates of interest, and a variety of optical and mass spectrometric techniques are employed to probe the evolution of reactants and products. The experimental results provide needed input into models of atmospheric transport and chemical transformation that are employed to understand phenomena such as global climate change, stratospheric ozone depletion, urban air quality, and acid precipitation. Results of our studies also provide fundamental information that is useful for establishing free radical thermochemistry and for refining reaction rate theories. We are interested in gas-phase chemistry as well as chemistry that occurs in the atmospheric condensed phase, i.e., on the surfaces or in the bulk of cloud droplets and/or aerosol particles.
Brief Descriptions of Specific Projects
Laboratory Studies of Tropospheric Sulfur Chemistry (sponsored by NSF)
There is currently enormous interest in understanding atmospheric sulfur oxidation in order to facilitate (1) our understanding of past climate as interpreted from ice core analyses and (2) our understanding of the role sulfur plays in particle formation and growth in the atmosphere and its resulting impact on current and future climate.
Our research focuses on elucidating the kinetics and reaction mechanisms that control the atmospheric oxidation of dimethylsulfide (CH3SCH3, DMS), the most ubiquitous naturally-occurring sulfur compound in the atmosphere, and its intermediate oxidation products dimethylsulfoxide (CH3S(O)CH3, ) and methanesulfinic acid (CH3S(O)OH, MSIA).
The goal of this research is the definitive determination of the rates and mechanisms for conversion of DMS, , and MSIA into the relatively stable S(VI) end products sulfuric acid (H2SO4) and methanesulfonic acid (CH3(O)S(O)OH, MSA) as well as their deprotonated condensed phase analogues sulfate and methanesulfonate; it is these non-volatile S(VI) end products which are implicated in particle formation and growth in the atmosphere. Understanding their yields from DMS oxidation over the range of conditions encountered in the atmosphere is a prerequisite for assessing the contribution of biogenic and anthropogenic sulfur to climate modification or regulation as well as other environmental issues such as visibility reduction, acid precipitation, and lower stratospheric ozone depletion.
Collaborators
Laboratory Investigations of Stratospheric and Upper Tropospheric Chemistry (sponsored by NASA)
Although the abundance of ozone in the atmosphere is quite small, i.e., 3 ozone molecules per 10,000,000 air molecules on average, ozone is a key atmospheric trace gas. The stratospheric "ozone layer" protects the biosphere from harmful ultraviolet radiation, thus allowing the existence of life as we know it. In the lowest regions of the atmosphere, ozone is a nuisance. It is a powerful oxidant that is harmful to plants and animals, and it is a key player (both as an initiator and as an ultimate product) in photochemical smog. The atmospheric chemistry of ozone is complex, involving numerous catalytic chain reactions. This research project involves laboratory studies aimed at quantitatively characterizing the complex chain reaction sequences via which HOx, NOx, ClOx, BrOx, and IOx radicals catalytically destroy ozone. The results of our studies are used in prognostic models that predict the impacts of anthropogenic activity on future ozone levels, and the resulting impacts on climate and biological activity.
Collaborators
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