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 normal ized by total particle number and plotted against a scaled diameter. Distin ctly different characteristic distributions are observed for direct injecti on and for port injection gasoline vehicles. These signature distributions are compared to numerically calculated self-preserving size distributions w hich incorporate fractal dimensions less than or equal to 3 to describe the dendritic nature of soot. However, the coagulation models alone are incapa ble of reproducing the observed characteristic distributions; compared to t he diesel engine data they are conspicuously asymmetric and too steep on th e large particle diameter side of the distribution. We discuss the possibil ity that soot oxidation also plays a role in determining the shape of the c haracteristic distributions, and the possibility that these signatures coul d be utilized to distinguish soot emissions from other aerosols. (C) 2001 E lsevier Science Ltd. All rights reserved.