Photochemical oxidants: state of the science

Atmospheric photochemical processes resulting in the production of troposph eric ozone (O-3) and other oxidants are described. The spatial and temporal variabilities in the occurrence of surface level oxidants and their relati onships to air pollution meteorology are discussed. Models of photooxidant formation are reviewed in the context of control strategies and comparisons are provided of the air concentrations of O-3 at select geographic locatio ns around the world. This overall oxidant (O-3) climatology is coupled to h uman health and ecological effects. The discussion of the effects includes both acute and chronic responses, mechanisms of action, human epidemiologic al and plant population studies and briefly, efforts to establish cause-eff ect relationships through numerical modeling. A short synopsis is provided of the interactive effects of O-3 With other abiotic and biotic factors. Th e overall emphasis of the paper is on identifying the current uncertainties and gaps in our understanding of the state of the science and some suggest ions as to how they may be addressed. (C) 1999 Published by Elsevier Scienc e Ltd. All rights reserved.