Benzene Exhaust Emissions from I n-Use General Motors Vehicles Jean Muhlbaier Dasch" and Ronald L. Williams Environmental Science Department, General Motors Research Laboratories, Warren, Michigan 48090-9055
Benzene emissions were measured from the exhaust of 73 in-use, light-duty vehicles. Benzene averaged 27 mg/ mile for 1981/.1982 model year cars and decreased to 9.4 mg/mile for 1983-1987 cars. Hydrocarbon emissions also decreased after 1982 as closed-loop systems and fuel control improved. Benzene emissions showed a modest increase with mileage: the base-line benzene was 6.6 mg/mile with an increase of 1.0 mg/mile for each additional 10000 miles of travel. Lower levels of benzene were emitted from dual-bed catalysts than from three-way catalysts. However, since many engine modifications were made during the period when dual-bed catalysts were replaced with three-way catalysts, a direct comparison is difficult. In a recent EPA paper, benzene emissions were calculated to be 102-119 mg/mile for the 1986 vehicle fleet. Based on the in-use values measured in this study of 9.4 mg/mile for 1983-1987 vehicles, substantial decreases in the fleet average are expected as these newer vehicles dominate the vehicle fleet. Introduction Benzene was declared a hazardous air pollutant under section 112 of the Clean Air Act. According to a recent EPA source inventory, 85% of benzene emissions in the United States is from mobile sources, of which 70% is from exhaust, 14% from evaporative emissions, and 1% from vehicle refueling (1). Benzene has been measured from automobiles in several studies. Precatalyst cars averaged 114 mg/mile from 14 cars (2), 123 mg/mile from 3 cars (3),or 153 mg/mile from 1 car ( 4 ) in three studies. Tests on catalyst cars show average emissions of 5 mg/mile from 2 cars (51, 7.5 mg/ mile from 41 cars (6), 9 mg/mile from 41 cars (71, 11 mg/mile from 5 cars (8), 13 mg/mile from 4 cars ( 3 ) ,15 mg/mile from 9 cars (9),20 mg/mile from 5 cars (IO),21 mg/mile from 24 cars (2), 27 mg/mile from 2 cars (4), and 32 mg/mile from 211 cars (11). This compilation is based on the most representative tests in these studies whenever possible, Le., Federal Test Procedure driving cycles at room temperature with typical composition gasoline and excluding special groups of malfunctioning vehicles. Benzene emissions are related to the benzene level of the fuel as well as the total aromatic level of the fuel (4, 6,8, 12). Some of the differences in the above studies can be related to different fuels. In addition, many of those studies were on older cars, before three-way catalysts were introduced. In this study, benzene was measured in the exhaust of 73 late-model, in-use vehicles. The same fuel was used throughout to eliminate the effect of fuel differences on emissions. The results will be examined for 0013-936X191/0925-0853$02.50/0
the effect of model year, mileage, fuel distribution system, and catalyst type. Procedure Vehicles. Benzene was measured from cars being tested under two different programs. Under the ongoing General Motors in-use emissions performance program, about 500 GM cars from each model year are solicited from owners 2-3 years after purchase (13). Benzene was tested from 55 of these cars and light-duty trucks, as received, covering the model years 1985-1987. One benzene measurement was made per vehicle. Cars were also tested under the Cooperative Test Program (CTP) between the car manufacturers and EPA (14). Under this program, GM cars that had failed the Michigan Auto Exhaust Testing (AET) program were tested for regulated emissions as received and during the repair process. When the hydrocarbon (HC) levels were
