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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.

Particulate emissions from 20 light-duty gasoline passenger cars and trucks were characterized using the Federal Test Procedure and Highway Fuel Economy Test driving cycles. Emission patterns were examined with 4 of the vehicles using three additional driving cycles, the hot start Federal Test Procedure, the Congested Urban Expressway and the New York City. The test fleet consisted of 4 noncatalyst vehicles operated with leaded gasoline and 16 catalyst-equipped vehicles operated with unleaded gasoline. The vehicles, obtained from local rental agencies, dealers, and residents, ranged in age from model year 1970 through 1981 and in mileage accumulation from about 300 to 81,000 miles. Particulate characterization included determination of total particulate emission rates, Ames bioassay of the dichloromethane soluble organic fraction, and analysis of the nitropyrene, pyrene, benzo-a-pyrene, and trace elements content.

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.

Apportionment of air pollution to sources requires knowledge of source emission strengths and/or chemical and physical characteristics. The literature is deficient in data useful for this purpose for heavy-duty motor vehicles, which can be important sources of air pollution in certain microenvironments. Emission factors are developed in this study for heavy-duty gasoline trucks using chassis dynamometer simulations of urban driving conditions. The sensitivity of the emissions to such considerations as the characteristics of the speed-time driving schedule, vehicle payload, and chassis configuration are examined. Emissions characterization includes total and individual hydrocarbons, aldehydes, carbon monoxide, oxides of nitrogen, total particulate matter, particulate organics, lead, bromine, chlorine, and the fraction of total particulate less than 2 μm. Preliminary comparisons of emissions obtained using transient engine and transient chassis test procedures are also reported.