Measurements of nitrous oxide emissions from light-duty motor vehicles: a pilot study

Dynamometer testing in conjunction with high-resolution FTIR spectroscopy was used to measure exhaust emissions of nitrous oxide (N2O) from a fleet of 37 light-duty vehicles at the California Air Resources Board. Exhaust emissions were collected for two driving cycles: the Urban Dynamometer Driving Schedule and the Unified Cycle. The vehicles studied, including passenger cars, sport utility vehicles, and light-duty trucks, were a sub-sample of a fleet that represented Californiaʹs in-use fleet. The highest correlation between the emissions of N2O and other vehicle-exhaust species was, as expected, between N2O and nitrogen oxides (r2=0.45). The previously reported impact of catalyst aging on N2O emissions could not be verified by our data. Type of catalyst, driving cycle, and vehicle were demonstrated to be the main factors determining the magnitude of N2O emissions from gasoline-powered light-duty vehicles. The average N2O emissions factor for the 37 vehicles tested was 20±4 mg km−1, with a factor of 50 difference between the lowest (2 mg km−1) and highest (100 mg km−1) N2O emissions. The average value for N2O/NOx emissions ratios was 0.095±0.035, with a factor of 14 difference between the lowest (0.01) and the highest (0.14) ratios.