BENZENE EXHAUST EMISSIONS FROM IN-USE GENERAL-MOTORS VEHICLES

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 10 000 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.