ANALYSIS OF MOTOR-VEHICLE SOURCES AND THEIR CONTRIBUTION TO AMBIENT HYDROCARBON DISTRIBUTIONS AT URBAN SITES IN TORONTO DURING THE SOUTHERNONTARIO OXIDANTS STUDY

Hydrocarbon distributions measured in the urban area of Toronto during the Southern Ontario Oxidants Study of 1992 are presented. Comparison is made to hydrocarbon distributions measured in other urban areas. R elative concentrations of olefins were found to be depleted aloft comp ared to the surface level measurements, Chemical mass balance modellin g was used to apportion the measured hydrocarbon distributions at York University and other roadside sites to gasoline based sources. The mo st dominant contributing source was vehicle exhaust. The relative amou nt of unburned gasoline at York University was found to be significant in the summer, and higher than that observed there during the winter or at other roadside sites. The relative amount of evaporative emissio ns (gasoline vapour) apportioned by the CMB model at roadside sites wa s compared to evaporative emissions predicted by a mobile emission fac tor model, MOBILE5C, The percentage of gasoline based non-methane hydr ocarbons (NMHC) apportioned to gasoline vapour by the CMB model was eq uivalent within error to the relative amount of evaporative NMHC predi cted by the MOBILE5C model for summer temperatures. For winter tempera tures, the MOBILE5C model predicted significantly less evaporative emi ssions than that apportioned by the CMB model. An anthropogenic source of isoprene in the urban area has been proposed and tested. The inclu sion of an isoprene flux in the exhaust source profile, consistent wit h that measured in the Auto/Oil Air Quality Improvement Research Progr am, results in calculated isoprene concentrations that are in agreemen t with observed concentrations at roadside sites and at York Universit y in the winter. During summer, the combustion related isoprene can on ly account for a small fraction of the observed isoprene at downtown s ites and at York University, at most 20%. Copyright (C) 1995 Elsevier Science Ltd