No abstract

No abstract

Methane (CH4) is an important greenhouse gas emitted by vehicles. We report results of a laboratory study of methane emissions using a standard driving cycle for 30 different cars and trucks (1995-1999 model years) from four different manufacturers. We recommend the use of an average emission factor for the U.S. on-road vehicle fleet of (g of CH/g of CO2) = (15 +/- 4) x 10(-5) and estimate that the global vehicle fleet emits 0.45 +/- 0.12 Tg of CH4 yr(-1) (0.34 +/- 0.09 Tg of C yr(-1)), which represents < 0.2% of anthropogenic CH4 emissions. This estimate includes the effects of vehicle aging, cold start, and hot running emissions. The contribution of CH4 emissions from vehicles to radiative forcing of climate change is 0.3-0.4% of that of CO2 emissions from vehicles. The environmental impact of CH4 emissions from vehicles is negligible and is likely to remain so for the foreseeable future.

Assessment of the impact of vehicle emissions on the global environment requires accurate data concerning nitrous oxide, N 2 O, emissions. We report herein "realworld" 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 22 different cars and trucks. Consistent results were obtained from both approaches, suggesting that a good approximation of the average emission factor (g of N 2 O/g of CO 2 ) ) (6 ( 2) × 10 -5 . This corresponds to an emission rate of 16-8 mg of N 2 O/km for vehicles with fuel economies of 12-6 L/100 km (20-40 mi/U.S. gal). N 2 O emissions from vehicles have a global warming impact, which is 1-3% of that of the CO 2 emissions from vehicles. We estimate that the global vehicle fleet emits 0.18 ( 0.06 Tg of N 2 O 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 N 2 O, laboratory vehicle emission measurements of NH 3 , HONO, and HCN are reported.

No abstract