Particulate organic compounds emitted from motor vehicle exhaust and in the urban atmosphere

The emission rate of particle-phase petroleum biomarkers in vehicular exhau st compared to the concentrations of these biomarkers in ambient air is use d to determine the particulate organic compound concentration due to primar y particle emissions from motor vehicles in the southern California atmosph ere. A material balance on the organic particulate matter emitted from moto r vehicle traffic in a Los Angeles highway tunnel first is constructed to s how the proportion which is solvent-extractable and which will elute from a GC column, the ratio of resolved to unresolved compound mass, the portion of the resolved material that can be identified as single organic compounds , and the contribution of different classes of organic compounds to the ove rall identified fraction. It is shown that the outdoor ambient concentratio ns of the petroleum biomarkers track primary emissions measured in the high way tunnel, confirming that direct emissions of these compounds from vehicl es govern the observed ambient petroleum biomarker concentrations. Using or ganic chemical tracer techniques, the portion of fine organic particulate m atter in the Los Angeles atmosphere which is attributable to direct particl e emissions from vehicle exhaust is calculated to vary from 7.5 to 18.3% at different sites throughout the air basin during a summertime severe photoc hemical smog episode. A similar level of variation in the contribution of p rimary motor vehicle exhaust to fine particulate organic matter concentrati ons during different times of day is seen. While peak atmospheric concentra tions of fine particulate organic carbon are observed during the 1200-1600 PDT afternoon sampling period, only 6.3% of that material is apportioned to the directly emitted particles from vehicle exhaust. During the morning tr affic peak between 0600-1000 PDT, 19.1% of the fine particulate organic mat erial is traced to primary emissions from motor vehicles. (C) 1999 Elsevier Science Ltd. All rights reserved.