General Motors Sulfate Dispersion Experiment: Summary of EPA Measurements

Abstract

In October 1975, General Motors sponsored a study of sulfate exposures utilizing a fleet of catalyst equipped motor vehicles in controlled, simulated, highway driving conditions. This paper reports some EPA sponsored measurements. Sulfuric acid aerosol, in the Aitken nuclei mode, geometric mean diameter (GMD) of about 0.02 µm, is emitted in the exhaust of catalyst equipped vehicles. Measurement of sulfuric acid 20 m downwind of the roadway indicated a lack of complete neutralization by ammonia. When the wind was perpendicular to the roadway there was little coagulation of sulfuric acid into the accumulation mode, GMD of about 0.24 µm From measurement of the mass flow rate of aerosol sulfur from the simulated freeway, the aerosol sulfur emission rate per car was determined to be 3.5 ± 0.8 µg/m (5.6 ±1.3 mg/mile) corresponding to a 12 ± 3% conversion of fuel sulfur into emitted aerosol sulfur. © Taylor & Francis Group, LLC.