Chemical source profiles for particulate motor vehicle exhaust under cold and high altitude operating conditions

Abstract

The chemical compositions of fine particles in motor vehicle exhaust were measured on dynamometer and in situ exhaust samples during the winter in Denver, CO (elevation ∼ 1600 m above sea level). Forty-one inorganic and other species were quantified for tests involving different vehicle types, different fuels, and different operating cycles. It was found that addition of ethanol or MTBE (methyl tertiary butyl ether) to leaded and unleaded gasoline (in order to lower CO emissions) has no major effect on the chemical composition of particulate emissions from motor vehicles. On the Federal Test Procedure (FTP) driving schedule but at temperatures of 0 to 5 °C to simulate Denver winter conditions, compositions of emissions were similar among the cold-transient, cold-stabilized, and hot-transient cycles in the case of the leaded-fuel vehicles and also in the case of the diesel vehicles. Cold starts do cause a major change in the composition of emissions from unleaded catalyst-equipped vehicles by increasing the elemental carbon. Two-stroke diesel buses emit a much higher fraction of organic carbon and a much lower fraction of elemental carbon than do cars or four-stroke diesel trucks.