Atmospheric chemistry and measurements of vehicle-derived polycyclic aromatic compounds

Polycyclic aromatic compounds (PACs) are ubiquitous environmental contaminants released into ambient atmospheres from incomplete combustion sources. In urban areas, vehicle emissions are a major contributor to ambient PAC concentrations. Although toxicological and epidemiological studies have been conducted on the health effects of freshly emitted vehicle exhaust, little is known about the toxicity of aged vehicle emissions. In fact, the volatile and semi-volatile PACs emitted into the atmosphere can undergo gas-phase reactions with hydroxyl and nitrate radicals, ozone or photolyze. Products of these atmospheric reactions include mutagenic nitro-PACs and potentially toxic oxygenated PACs. The identification of the atmospheric transformation products is therefore a necessary first step before their health effects can be assessed.; In this work, atmospheric reactions are simulated in environmental chambers to study atmospheric reaction mechanisms of vehicle-derived volatile organic compounds, including polycyclic aromatic hydrocarbons (PAHs). Ambient measurements were done to assess the presence of atmospheric reaction products that were identified under laboratory conditions.; Potentially toxic oxygenated compounds have been identified as a major class of compounds formed from atmospheric OH radical-initiated gas-phase reactions. A derivatization method using solid-phase microextraction fibers was developed to enable their analysis. Environmental chamber studies have also been performed to study the atmospheric lifetimes and reaction products of two vehicle-derived PAHs, acenaphthene and acenaphthylene, resulting in a better understanding of their reaction mechanisms. Additionally, studies of photooxidized volatilized diesel fuel were carried out to determine the presence of nitro-alkylnaphthalenes. Ambient measurements, that were conducted in summer and winter at both a source site (Los Angeles, CA) and a downwind receptor site (Riverside, CA), showed the importance of atmospheric reactions as a contributor to ambient nitro-PAHs.