Publication Date


Document Type


Organizational Units

Chemistry and Biochemistry


Atmospheric chemistry, Emissions, Pollutants


Repeated, fuel specific, emission measurements in Denver (2005/2013), Los Angeles (2008/2013) and Tulsa (2005/2013) provide long-term trends in on-road reactive nitrogen emissions from three light/medium duty U.S. fleets. Reductions in oxides of nitrogen (NOx) emissions ranged from 21% in Denver (5.6 ± 1.3 to 4.4 ± 0.2 gNOx/kg of fuel) to 43% in Tulsa (4.4 ± 0.3 to 2.5 ± 0.1 gNOx/kg of fuel) since 2005 while decreases in fleet ammonia (NH3) emissions ranged from no change in Denver (0.45 ± 0.09 to 0.44 ± 0.02 gNH3/kg of fuel) since 2005 to a 28% decrease in LA (0.80 ± 0.02 to 0.58 ± 0.02 gNH3/kg of fuel) since 2008. The majority of the reduction in gasoline vehicle NOx emissions occurred prior to the full implementation of the Tier II emission standards in 2009. High in-use NOx emissions from small engine diesel passenger vehicles produced a significant contribution to the fleet means despite their small numbers. NH3 emissions decreased at a slower rate than NOx emissions due to modest NH3 emissions reduction among the newest vehicles and increased emissions from a growing number of older vehicles with active catalytic converters. In addition, the reactive nitrogen emissions from many new model year vehicles are now dominated by NH3.

Copyright Statement / License for Reuse

Creative Commons Attribution-NonCommercial 4.0 International License
This work is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License

Publication Statement

This is an Accepted Manuscript for

Bishop, G. A.; Stedman, D. H. (2015) Reactive Nitrogen Species Emission Trends in Three Light-/Medium-Duty United States Fleets. Environ. Sci. Technol., 49(18), 11234-11240. DOI: 10.1021/acs.est.5b02392.

Copyright held by the American Chemical Society. User is responsible for all copyright compliance.