SPECIATED MEASUREMENTS AND CALCULATED REACTIVITIES OF VEHICLE EXHAUST EMISSIONS FROM CONVENTIONAL AND REFORMULATED GASOLINES

Exhaust emissions were characterized from 19 vehicles tested with two fuels: a typical Los Angeles premium gasoline and a reformulated premium gasoline. The reformulated fuel had lower vapor pressure and distillation temperatures than the reference fuel and contained 11 vol % methyl-tert-butyl ether (MTBE). Total volatile organic compounds (VOC) emissions were reduced with the reformulated fuel by 6% across the 19 vehicles, but aldehyde and alkene emissions were increased. The reactivity of exhaust emissions was estimated by applying maximum incremental reactivity (MIR) factors to the speciated emission profiles. Total reactivity (g of ozone/mile) varied linearly with emission rate across all vehicles. Mass-normalized reactivity (g of ozone/g of non-methane organic gases) was not different for the two fuels but did vary somewhat from vehicle to vehicle. On average, mass-normalized reactivity was reduced slightly in progressing from older to newer technology types. Relative to fuel compositions, exhaust compositions were depleted in alkanes and aromatics but enriched in alkenes and carbonyls. The alkene enrichment resulted from combustion-produced C2-C4 species and was responsible for much of the overall reactivity of the emissions.