Assessment of the impact of vehicle emissions on the global environment requires accurate data concerning nitrous oxide, N{sub}2O, emissions. We report herein "real-world" N{sub}2O 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 goodapproximation of the average emission factor (g of N{sub}2O/g of CO{sub}2) = (6±2)×10{sup}-5 This corresponds to an emission rate of 16-8 mg of N{sub}2O/km for vehicles with fuel economies of 12-6 L/100 km (20-40 mi/U.S. gal). N{sub}2O emissions fromvehicles have a global warming impact, which is 1-3 of that of the CO{sub}2 emissions from vehicles. We estimate that the global vehicle fleet emits 0.18±0.06 Tg of N{sub}2O yr{sup}-1 (0.11±0.04 Tg of N yr{sup}-1), which represents 2-6 of theatmospheric growth rate of this species. In addition to N{sub}2O, laboratory vehicle emission measurements of NH{sub}3, HONO, and HCN are reported.
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