Submicrometer and Supermicrometer Particles from Diesel Vehicle Emissions

There is growing evidence that fine airborne particulates could play the most important role in determining health effects. The aim of this work was to investigate the number concentration and size distributions of particulates in the exhausts of diesel vehicles (mainly buses) of different ages and make, operating under different loads. Particle-sizing instruments used were the Scanning Mobility Particle Sizer (SMPS) and Aerodynamic Particle Sizer (APS). The average particle number concentration of the exhausts was in the range (0.7−3.9) × 107 cm-3 in the SMPS range (0.0075−0.304 μm) and (0.3−32) × 103 cm-3 in the APS range (0.5−30 μm). In most cases, particle number concentrations increased with the increased power output from the engine and, in both SMPS and APS ranges, varied significantly within each group of vehicles, but the differences between the groups were small. For individual vehicles, there was no relation between emissions in the smaller and larger particle ranges. Emission characteristics did not appear to be correlated with engine model or age. The implications of these findings to particle emission testing and control as well as to exposure and risk analysis are discussed.