Research in atmospheric chemistry has the ultimate goal of simulating by mathematical modeling any complex system of coupled chemical reactions in the atmosphere. The result can be the capability of predicting any changes in the composition of the atmosphere resulting from varying natural conditions or the introduction of man-made contaminants. The resolution of important practical and scientific problems requires the acquisition of the best possible values of the reaction speeds (kinetic constants) of the may elementary steps that make up the chemistry of the atmosphere. Among these problems are the stability of the stratospheric ozone layer, the appearance in urban air of secondary pollutants that were not present in the emissions of any contaminating source, and the course of evolution of planetary atmospheres, including the atmosphere of our own planet. This project attacks one of the most difficult, but necessary, aspects of atmospheric chemistry - the measurement of the reaction rates for chemical processes involving free radicals, most of which are unstable and extremely reactive fragments of the stable molecules of the atmosphere. Because they are so reactive, they occur in exceedingly low concentrations and are therefore measurable only by highly sophisticated techniques. It is their high reactivity, however, that makes them such active participants in the chemistry of the air and can allow them to determine the fate of more abundant species, such as hydrocarbons, sulfur dioxide, ozone, etc. The project will measure the reaction rates for several key chemical processes involving radical-radical and radical-molecule interactions in the sulfur, nitrogen, halogen, oxygen and hydrogen systems. These systems are important elements in contemporary approaches to the chemistries of clean and polluted air.
