Gas-Phase and Particle-Phase Organic Compounds Emitted from Motor Vehicle Traffic in a Los Angeles Roadway Tunnel

Abstract

The emission rates for 221 vapor-phase, semivolatile, and particle-phase organic compounds from motor vehicles plus fine particulate matter mass and some inorganic particle-phase species are calculated based on measurements made inside and outside a Los Angeles roadway tunnel in 1993. These emission rates are calculated based on fuel consumption to remove any uncertainties based on tunnel dilution rates or air circulation. The results show carbon monoxide emissions rates of 130 g L -1 of gasoline-equivalent fuel burned and volatile organic compound (VOC) emissions of 9.1 g L - 1 . These values are higher than predicted by the baseline version of California's EMFAC 7G emissions inventory program but are within the coemission rate range of 108 ± 25 g L -1 reported by roadside remote sensing studies in Los Angeles [Singer, B. C.; Harley, R. A. J. Air Waste Manage. Assoc. 1996, 46, 581−593]. When the VOC emissions composition in the tunnel is compared to that of tailpipe emissions source test data and to the composition of additional unburned whole gasoline, the tunnel atmosphere is found to be consistent with a linear combination of these major contributors over a fairly broad range of about 74−97% vehicle exhaust depending on the tailpipe profiles used. Fine particulate emissions within the tunnel consist largely of carbonaceous material accompanied by a significant amount of ammonium nitrate apparently formed by gas-to-particle conversion processes within the tunnel atmosphere. Certain gas-phase and particulate organic compounds traditionally thought to be the secondary products of atmospheric chemical reactions are enriched inside the tunnel, and from this enrichment, the primary emission rates of aromatic alcohols, aliphatic dicarboxylic acids, and aromatic polycarboxylic acids are calculated. Data on petroleum biomarkers emissions rates in the tunnel can be used in the future to estimate primary vehicle exhaust fine particulate matter concentrations in the urban atmosphere.