The organic compound, isoprene, is an extremely important, naturally emitted species that contributes to the chemistry of the troposphere on regional and global scales. The details of the photochemical degradation have been studied for some time, but there remain gaps in our understanding of rate coefficients and mechanisms of specific processes, particularly under conditions of low oxides of nitrogen (NOx) concentrations. This study will link expertise at two institutions (State University of New York College of Environmental Science and Forestry, and Mississippi State University) in (1) producing specific isoprene derived peroxy radicals (RO2) with (2) new detection methods based on cavity ring down spectroscopy (CRDS) in the near infrared spectral region. The tasks of this project are to produce peroxy radicals that are generated from the attack of hydroxyl radicals (OH) on isoprene, assign spectra to particular isomers, and determine absorption cross sections. Then rate coefficients for the reactions of these peroxy radicals with NO (nitric oxide), HO2 (hydroperoxyl radicals), as well as the radical self reaction, will be quantified. From these kinetic data, branching ratios to various product channels will be assessed. In addition, results of detailed quantum chemical calculations will be compared with the experimental results in order to develop predictive structure-activity relationships.
The results of this research will lead to improved chemical mechanisms for isoprene degradation in the atmosphere, thereby improving chemical transport models of various degrees of sophistication. The chemistry of related compounds (e.g. 1,3-butadiene, 2-methyl-but-3-en-2-ol, and terpenes) will also be better understood through results of this research. The oxidizing capacity of the global atmosphere will thus be better constrained, given that these species together have an extremely large influence on it. In short, this work will improve understanding of the atmospheric chemistry of isoprene and related species. The educational aspects are significant, since a graduate student, a postdoctoral fellow, and several undergraduate students will be trained in areas of laser spectroscopy, kinetics, atmospheric and quantum mechanical modeling, and biosphere-atmosphere interactions. In addition, collaboration between the investigator's institutions (SUNY College of Environmental Science and Forestry, and Mississippi State University) will be fostered.