Numerous pollution control agencies around the world are attempting to impl
ement smoke opacity tests in efforts to lower ambient fine particulate matt
er levels. However, this approach is valid only if lower smoke opacity leve
ls do result in lower mass emissions rates and lower number count of partic
ulate matter emissions. This paper is limited to measurements of mass emiss
ion rates of particulate matter and smoke opacity. Particle size distributi
ons and concentrations are not discussed. Ln this study in-use emissions we
re measured from eighteen transit buses powered by electronic controlled si
x-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 Te
st procedure using a partial flow smoke meter, Bosch RTT 100 Diesel Smoke O
pacimeter. Raw smoke opacity data was analyzed using the running half-secon
d 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. Th
e vehicles were operated over the Central Business District cycle on the ch
assis-dynamometer based laboratory. While smoke opacity and mass emission r
ates of particulate matter from heavy-duty vehicles do exhibit a trend, the
re is no correlation between these two measurements.