On-road measurement of ammonia and other motor vehicle exhaust emissions

Ammonia is the primary alkaline gas in the atmosphere and contributes to fi ne particle mass, visibility problems, acid dry and wet deposition. The obj ective of this research was to measure ammonia and other exhaust emissions from a large sample of on-road vehicles using California phase 2 reformulat ed gasoline with low sulfur content (similar to 10 ppm by weight). Vehicle emissions of ammonia, NOx, CO, and CO2 were measured in the center bore of a San Francisco Bay area highway tunnel on eight 2-h afternoon sampling per iods during summer 1999. Ammonia concentrations were divided by total carbo n (mainly CO2) concentrations to compute an emission factor of 475 +/- 29 m g L-1 (95% C.I.). The molar ratio of nitrogen emitted in the tunnel in the form of ammonia to that emitted in the form of NOx was 0.27 +/- 0.01, Emiss ions of NOx and CO have been measured at this tunnel sampling location sinc e 1994, From 1994 to 1999, emissions decreased by 41 +/- 4% for N0(x) and 5 4 +/- 6% for CO. These reductions include the impacts of turnover in the ve hicle fleet and the use of reformulated gasoline. Between 1997 and 1999, wh en fuel properties did not change significantly, emissions of NO, and CO de creased by 26 +/- 2% and 31 +/- 3%, respectively. While use of three-way ca talytic converters has contributed to decreases in NO, and CO emissions, th eir use, in combination with fuel-rich engine operation, is the likely caus e of the ammonia emissions from motor vehicles observed during this study.