Nitrous Oxide (N₂O) Emissions from Vehicles

Abstract

Assessment of the impact of vehicle emissions on the global environment requires accurate data concerning nitrous oxide, N2O, emissions. We report herein “real-world” N2O emissions from road vehicles in a tunnel in Wuppertal, Germany, together with “laboratory” emission measurements conducted at the Ford Motor Company using a chassis dynamometer with a standard driving cycle for 22 different cars and trucks. Consistent results were obtained from both approaches, suggesting that a good approximation of the average emission factor (g of N2O/g of CO2) = (6 ± 2) × 10-5. This corresponds to an emission rate of 16−8 mg of N2O/km for vehicles with fuel economies of 12−6 L/100 km (20−40 mi/U.S. gal). N2O emissions from vehicles have a global warming impact, which is 1−3% of that of the CO2 emissions from vehicles. We estimate that the global vehicle fleet emits 0.18 ± 0.06 Tg of N2O yr-1 (0.11 ± 0.04 Tg of N yr-1), which represents 2−6% of the atmospheric growth rate of this species. In addition to N2O, laboratory vehicle emission measurements of NH3, HONO, and HCN are reported.