Particulate matter emissions and smoke opacity from in-use heavy-duty vehicles

Numerous pollution control agencies around the world are attempting to implement smoke opacity tests in efforts to lower ambient fine particulate matter levels. However, this approach is valid only if lower smoke opacity levels do result in lower mass emissions rates and lower number count of particulate matter emissions. This paper is limited to measurements of mass emission rates of particulate matter and smoke opacity. Particle size distributions and concentrations are not discussed. Ln this study in-use emissions were measured from eighteen transit buses powered by electronic controlled six-cylinder, turbocharged, after-cooled engines. Eleven of these were fueled with diesel no. 1 while the remaining were running on bio-diesel. Vehicle exhaust smoke opacity measurements were made using the Snap-Acceleration Test procedure using a partial flow smoke meter, Bosch RTT 100 Diesel Smoke Opacimeter. Raw smoke opacity data was analyzed using the running half-second average and the second order Bessel filter. In most cases the half-second average gave a higher peak value than the Bessel filter. The smoke opacity data was compared with the mass emission rates of total particulate matter that were obtained during transient testing of these vehicles on the West Virginia University Transportable Heavy-duty Vehicle Testing Laboratory. The vehicles were operated over the Central Business District cycle on the chassis-dynamometer based laboratory. While smoke opacity and mass emission rates of particulate matter from heavy-duty vehicles do exhibit a trend, there is no correlation between these two measurements.