Inorganic and organic peroxides are detected in the atmosphere and in rain, snow and fog, and there is evidence that their concentration has been increasing. Peroxides interfere with normal plant growth, and play an important role in the conversion of sulfur dioxide to sulfuric acid in cloud water. Photochemical air pollution involves a complex set of chemical reactions initiated by sunlight-generated free radicals. These reactions both consume and generate peroxides, and are the subject of active research aimed at developing effective pollution control strategies. Hydrogen peroxide concentration increases with solar intensity, but diurnal profiles of organic peroxides suggest an alternative source, possibly involving ozone and biogenic hydrocarbons. This research will involve laboratory and field studies aimed at a better understanding of peroxide occurrence and chemistry. The project scientists will develop the ability to detect trace concentrations of individual peroxides using high performance liquid chromatography with fluorescence detection, and study the rate at which individual peroxides deposit to grasslands and forest canopies. Undergraduate chemistry majors at a small four-year college will participate in all aspects of this Research in Undergraduate Institutions (RUI) project.