Evaluation of Nitrogen Oxide Emission Inventories and Trends for On-Road Gasoline and Diesel Vehicles

• Published in: Environmental science & technology 2021-05, Vol.55 (10), p.6655-6664
• Main Authors: Yu, Katelyn A, McDonald, Brian C, Harley, Robert A
• Format: Article
• Language: English
• Subjects: Anthropogenic Impacts on the Atmosphere; Chemical reduction; Diesel; Diesel engines; Diesel fuels; Emission analysis; Emission inventories; Emission measurements; Emission standards; Emissions; Emissions control; Engines; Evaluation; Gasoline; Gasoline engines; Internal combustion engines; Inventory; Nitrogen oxides; Photochemicals; Roads; Sales; Selective catalytic reduction; Trends
• ISSN: 0013-936X; 1520-5851
• DOI: 10.1021/acs.est.1c00586

On-road vehicles continue to be a major source of nitrogen oxide (NO x ) emissions in the United States and in other countries around the world. The goal of this study is to compare and evaluate emission inventories and long-term trends in vehicular NO x emissions. Taxable fuel sales data and in-use measurements of emission factors are combined to generate fuel-based NO x emission inventories for California and the US over the period 1990–2020. While gasoline and diesel fuel sales increased over the last three decades, total on-road NO x emissions declined by approximately 70% since 1990, with a steeper rate of decrease after 2004 when heavy-duty diesel NO x emission controls finally started to gain traction. In California, additional steps have been taken to accelerate the introduction of new heavy-duty engines equipped with selective catalytic reduction systems, resulting in a 48% decrease in diesel NO x emissions in California compared to a 32% decrease nationally since 2010. California EMFAC model predictions are in good agreement with fuel-based inventory results for gasoline engines and are higher than fuel-based estimates for diesel engines prior to the mid-2010s. Similar to the findings of recent observational and modeling studies, there are discrepancies between the fuel-based inventory and national MOVES model estimates. MOVES predicts a steeper decrease in NO x emissions and predicts higher NO x emissions from gasoline engines over the entire period from 1990 to 2020.