Optical systems unravel smog chemistry

Abstract

Application of tunable lasers and infrared Fourier transform spectroscopy to atmospherically important systems has led to the identification and quantification of a number of species in smog chambers, in laboratory experiments, and in the polluted troposphere. Many of these are labile molecules or free radicals whose presence had been previously postulated on sound kinetics and mechanistic grounds, but not directly observed. Others had not even been suspected to exist in atmospheric systems. Additionally, the development of tunable lasers has greatly aided elucidation of the mechanisms of certain important atmospheric reactions, including primary photodecomposition processes. The paper discusses recent studies with tunable lasers and Fourier transform infrared spectroscopy in which certain free radical and labile molecular species present in ambient and simulated atmospheres were directly identified and measured. These species are significant in oxidant control either because of their mechanistic role in establishing kinetic computer models, or alternatively, because of their potential effects on health and visibility, or both. These studies include the use of tunable uv laser systems to monitor OH radicals by their resonance fluorescence, the use of laser magnetic resonance in kinetic studies of OH, HO/sub 2/, and other free radicals, the use of lasers in studying themore » modes of photodecomposition of primary and secondary pollutants, the use of tunable lasers in elucidating the photochemistry of formaldehyde, the use of long pathlength optical systems, and Fourier transform infrared (FT-IR) spectrometers with interferometers.« less