Contribution of vehicle exhaust to the global N2O budget

Abstract Assessment of the impact of vehicle emissions on the global environment requires accurate data concerning nitrous oxide (N 2 O) emissions. We report herein `real world' N 2 O 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 26 different cars and trucks. Consistent results were obtained from both approaches suggesting that a good approximation of the average emission factor (g N 2 O/g CO 2 )=(4 ± 2) × 10 −5 . This corresponds to an emission rate of 11-5 mg N 2 O/km for vehicles with fuel economies of 12-6 l/100 km (20–40 miles/US gallon). N 2 O emissions from vehicles have a global warming impact, which is 1–2% of that of the CO 2 emissions from vehicles. We estimate an annual emission of (0.12±0.06) Tg yr −1 of N 2 O (0.08±0.04 Tg N yr −1 ) from the global vehicle fleet which represents 1–4% of the atmospheric growth rate of this species. These results update and supercede our previous study of N 2 O emissions from vehicles (Becker, K.H., Lorzer, J.C., Kurtenbach, R., Wiesen, P., Jensen, T., Wallington, T.J., 1999. Nitrous oxide (N 2 O) emissions from vehicles. Environ. Sci. Technol., 33, 4134–4139).