Signature size distributions for diesel and gasoline engine exhaust particulate matter

The size distributions of diesel exhaust particulate matter measured from a large number of vehicles and test engines, using a variety of diesel fuels, collapse onto a single characteristic lognormal distribution, when normalized by total particle number and plotted against a scaled diameter. Distinctly different characteristic distributions are observed for direct injection and for port injection gasoline vehicles. These signature distributions are compared to numerically calculated self-preserving size distributions which incorporate fractal dimensions less than or equal to 3 to describe the dendritic nature of soot. However, the coagulation models alone are incapable of reproducing the observed characteristic distributions; compared to the diesel engine data they are conspicuously asymmetric and too steep on the large particle diameter side of the distribution. We discuss the possibility that soot oxidation also plays a role in determining the shape of the characteristic distributions, and the possibility that these signatures could be utilized to distinguish soot emissions from other aerosols. (C) 2001 Elsevier Science Ltd. All rights reserved.