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There are many sources of variability when sampling motor vehicle emissions, including intermittant losses to “wetted” sampling system surfaces if water condensation occurs and thermal decomposition if sampling system surfaces get excessively hot. The risk of losses varies during typical transient speed emissions tests and depends upon many variables such as temperature, pressure, exhaust dilution ratio, dilution air humidity, fuel composition, and emissions composition. Procedures are described for injection of known concentrations of compounds of interest into transient motor vehicle exhaust for the purpose of characterizing losses between the vehicle tailpipe and emissions analyzer.

A series of emissions tests were completed with 2 light duty diesel passenger cars, a Volkswagen and Oldsmobile, to examine the sensitivity of emission rates and composition to fuel. Four fuels including 3 petroleum distillates and an oil shale distillate were used in the program. The tests included 6 driving schedules. Determinations of gaseous emission rates, including total hydrocarbon, carbon monoxide, and oxides of nitrogen, and particulate emission rates were completed. Compositional characterization of the particulate matter included dichloromethane soluble organic fraction, benzo(a)pyrene, pyrene, nitropyrene, Ames TA-98 bioassay, and trace elements. Both gaseous and particulate mass emission rates were insensitive to the fuels examined in this program. The polynuclear aromatic hydrocarbon compounds associated with the particles varied between fuels, but were not well correlated with the fuel polynuclear aromatic hydrocarbon content.