Contribution of vehicle exhaust to the global N2O budget

Assessment of the impact of vehicle emissions on the global environment requires accurate data concerning nitrous oxide (N₂O) emissions. We report herein `real world' N<sub>2</sub>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 N₂O/g CO₂)=(4 ± 2) × 10⁻⁵. This corresponds to an emission rate of 11-5 mg N₂O/km for vehicles with fuel economies of 12-6 l/100 km (20–40 miles/US gallon). N₂O emissions from vehicles have a global warming impact, which is 1–2% of that of the CO₂ emissions from vehicles. We estimate an annual emission of (0.12±0.06) Tg yr⁻¹ of N₂O (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 N₂O emissions from vehicles (Becker, K.H., Lörzer, J.C., Kurtenbach, R., Wiesen, P., Jensen, T., Wallington, T.J., 1999. Nitrous oxide (N₂O) emissions from vehicles. Environ. Sci. Technol., 33, 4134–4139).