ANTHROPOGENIC OZONE, ACIDS AND MUTAGENS - HALF A CENTURY OF PANDORA NOX

It has been four decades since the phenomenon of photochemical air pol lution was first characterized and, in the same year, a tragic London smog episode caused 4,000 excess deaths. Since then, there has been a substantial increase in our understanding of the chemistry involved in both types of air pollution, and a recognition that there is a very c lose chemical interrelationship between them. In this overview, we pro vide a brief historical perspective on the atmospheric chemistry of ph otochemical smog and illustrate how fundamental studies on the gas-pha se chemistry of uv-irradiated mixtures of volatile organic compounds ( VOC) and oxides of nitrogen (NO(x)) in polluted laboratory and ambient air masses have contributed to our understanding of three environment al problems: the atmospheric formation of ozone, nitric acid and airbo rne mutagens. In particular, we demonstrate the central role played by nitrogen dioxide and the hydroxyl radical in each case. We also show how certain reactive toxic and acidic species, e.g., formaldehyde and nitrous and formic acids, have been characterized in smog chambers and ambient smog by long pathlength spectroscopic techniques. It is shown that by using the same methods they now have been identified unequivo cally, along with NO2, in certain common types of polluted indoor atmo spheres ... and at much higher concentrations than outdoors. This has significant health implications for indoor HCHO and quite possibly the acids. We then trace the history of the direct mutagenicity of respir able particles in polluted ambient air and show how, through use of th e Ames test in biologically-directed assays of products coupled with f undamental studies of gas-phase reactions of polycyclic aromatic hydro carbons (PAH) and NO(x) in irradiated air, much of this activity can b e accounted for in terms of the formation of nitro-PAH and oxygenated derivatives. Finally, we discuss the application of basic kinetic, mec hanistic and analytical, experimental techniques and theoretical conce pts to the development of a new set of ''reactivity-based'' regulatory controls on motor vehicle emissions of VOC's. This novel regulatory a pproach applied by California's Air Resources Board, which takes effec t in 1994, illustrates the continuing need for fundamental research in the area of atmospheric chemistry and how it may be applied to ''real world'' environmental problems.