Sulfate Emissions from Vehicles on the Road

Experiments have been conducted to measure vehicle sulfate emissions, by vehicle type, at two tunnels on the Pennsylvania Turnpike. A satisfactory balance between estimated fuel sulfur consumption and observed emissions of sulfur compounds corrected for ambient-air contributions was obtained. This work started in 1974 before the introduction of catalyst-equipped automobiles and continued into 1976. The sulfate contributed by vehicles even in the tunnels was found to be generally modest relative to rural ambient sulfate levels. Average sulfate emission rates were found to be ~30 mg/km (50 mg/mi) from heavy-duty Diesel trucks, <15 mg/km from catalyst-equipped cars (probably in the range 4 to 7 mg/km), and probably <1 mg/km from non-catalyst cars. The overall SO₂ —* SO₄ ^-2 conversion of the vehicle emissions was 2 %.