NITRATION OF GASEOUS POLYCYCLIC AROMATIC-HYDROCARBONS IN SIMULATED AND AMBIENT URBAN ATMOSPHERES - A SOURCE OF MUTAGENIC NITROARENES

Recent results from field studies in the Los Angeles air basin which focused on the nature and concentrations of mononitroarenes in the gaseous and particulate states in polluted ambient air are reviewed. Relative concentrations in organic extracts of ambient particulate polycyclic organic matter (POM) were found to be, in decreasing order, 2-NO2-fluoranthene > 1-NO2-pyrene .gtorsim. 2-NO2-pyrene; this is in sharp contrast to primary emissions of diesel soot, where 1-NO2-PY .mchgt. 3-NO2-FL > 8-NO2-FL. Since light and heavy duty diesel motor vehicle emissions are a significant source of sub-.mu.m particles in the Los Angeles area, the relatively high abundance of 2-NO2-FL suggests that a significant fraction of the 2-NO2-FL in southern California may be formed via atmospheric reactions. In a wintertime 1986 study of a high-NOx episode .apprx. 20 km east of the Los Angeles International Airport, high concentrations of 1- and 2-nitronaphthalenes, much of which could have been in the gaseous state, were collected on a polyurethane backup ''plug'', along with lesser amounts of 2-NO2-FL (and 1- and 2-NO2-PY) adsorbed on the particles collected by a Hi-vol prefilter. Two gas phase mechanisms are proposed for the formation of adsorbed 2-NO2-fluoranthene and gaseous 2-NO2-naphthalene in urban air: (a) during daylight, attack on gaseous FL by OH radicals followed by NO2 addition, loss of H2O and condensation of 2-NO2-FL on particle surfaces and (b) reaction with N2O5 at night under ambient conditions during which the gaseous NO3 radical and NO2 are present, in equilibrium with N2O5. Chamber experiments with simulated polluted atmospheres support both of these mechanisms for the formation of 2-NO2-FL and 2-NO2-naphthalene; only the OH mechanism seems valid for 2-NO2-PY. Environmental and health implications of these studies are briefly discussed.