Sulfuric Acid Emissions from an Oxidation-Catalyst Equipped Vehicle

A 1973 Ford Torino with 1975 emission controls including monolithic noble metal catalysts was used to examine the effects of vehicle operating variables on sulfuric acid exhaust emissions. The vehicle was operated with and without the catalysts, at 60 mph and on an urban driving cycle (1975 FTP). H₂SO₄ and SO₂ were collected by a Goksϕyr-Ross condenser coil with hydrogen peroxide bubblers in series sampling from a dilution tunnel. Filter samples were collected from the tunnel for total particulate mass, sulfate, and pH measurements. The size distribution of the exhaust sulfate particulates was investigated by cascade impactor.

At 60 mph, 36 percent of the fuel sulfur was emitted as H₂SO₄. On the 1975 FTP driving cycle, the figure was 10 to 24 percent depending on prior operating history, with small differences between cold and hot-start and between transient and stabilized phases of the cycle. Sulfur storage in the converter was minor. The emitted H₂SO₄ was composed primarily of droplets smaller than 0.3 μm. Without catalysts, emission of H₂SO₄ is <1 percent of the fuel sulfur.