Size and composition distribution of fine particulate matter emitted from motor vehicles

A dilution source sampling system is augmented to measure the size-distribu ted chemical composition of fine particle emissions from motor vehicles. Me asurements are made using an optical particle counter (OPC), a differential mobility analyzer (DMA)/condensation nucleus counter (CNC) combination, an d a pair of microorifice uniform deposit impactors (MOUDIs). The sources te sted with this system include catalyst-equipped gasoline-powered light-duty vehicles, noncatalyst gasoline-powered light-duty vehicles, and medium-dut y diesel trucks. Chemical composition analysis demonstrates that particles emitted from the gasoline-powered vehicles tested are largely composed of o rganic compounds while particles emitted from diesel engines contain roughl y equal amounts of organic compounds and elemental carbon. The particle mas s distributions from all mobile sources tested have a single mode that peak s at approximately 0.1-0.2 mu m particle diameter. Of the two diesel vehicl es tested, the vehicle with the lowest fine particle emissions rate release d the largest number of ultrafine particles, a finding similar to that of B agley et al. (Characterization of fuel and aftertreatment device effects on diesel emissions, Technical Report 76; Health Effects Institute: Cambridge , MA, 1996). Particle size distribution measurements taken throughout the F TP urban driving cycle used to test all of the vehicles described in this p aper reveal that particulate mass emission rates and particulate size distr ibutions from the vehicles tested here are similar during the cold start an d hot start segments of the driving cycle.