Statistical Analysis of On-Road Particulate Matter Emissions from Diesel Vehicles

During 1996 and 1997, a number of light-and heavy-duty diesel vehicles were recruited in the Denver metropolitan area and subjected to emissions testing, principally for the purposes of assessing on-road particulate emissions. Little if any comparable data had been collected at altitude, particularly from heavy-duty vehicles. When these data were statistically examined using the technique of analysis of variance, they were shown both to exceed the federal standards, on average, and to be highly variable. These findings suggest that typically reported average values of vehicular PM emissions are not sufficient to be used, by themselves, to estimate contamination levels and associated public health risk. The situation is exacerbated in studies involving small numbers of vehicles, which is typical when diesel vehicles are involved, since not all sources of variation can be simultaneously controlled. Precise knowledge of the amount of particulates emitted by diesel vehicles in actual daily use is important because of present government strategies designed to promote the use of diesel as a transportation fuel.