ATMOSPHERIC CHEMISTRY OF TROPOSPHERIC OZONE FORMATION - SCIENTIFIC AND REGULATORY IMPLICATIONS

Tropospheric ozone continues to be of significant concern worldwide du e to its effect on human health, forest ecosystems and agricultural cr ops. Its levels have also increased globally over the last century. Ph otolysis of ozone (O3) is the major source of the hydroxyl (OH) radica l in the remote troposphere, so that an increase in O3 will produce mo re OH, resulting in decreased lifetimes of many trace species, such as methane and the hydrochlorofluorocarbons (HCFC), which are of stratos pheric importance. A brief overview of the chemistry of volatile organ ic compounds (VOC) and oxides of nitrogen (NO(x)) which lead to ozone formation is included. The question of whether controlling VOC or NO(x ) or both is most effective in urban/suburban and downwind/rural regio ns is discussed. The impact of uncertainties in emissions inventories is briefly discussed. Finally, the relative contributions of individua l VOC to ozone formation and how this information forms the technical basis for California's new regulations for VOC and concurrent NO(x) em issions from passenger cars and light-duty trucks is described. We bel ieve that the weight of past experience and current evidence supports strict concurrent controls on both NO(x) and VOC as essential to effec tive overall control of tropospheric ozone.