Publication Date


Document Type


Organizational Units

Chemistry and Biochemistry


Atmospheric chemistry, Emissions, Pollutants, EMFAC


On-road remote sensing measurements of light and medium-duty gasoline vehicles collected within California’s South Coast Air Basin since 1999 generally fall within the range of observed summer ambient molar NOx/CO measurements collected during morning rush hours. Compared with ambient and on-road emissions, the California Air Resources Board EMFAC model under predicts 2018 gasoline vehicle NOx emission factors by more than a factor of 2.6. Contributing to these differences is that vehicles older than model year 2006 have NOx emission deterioration rates that are up to 4 time’s higher on-road than predicted by the EMFAC model. A fuel-based inventory using the 2018 on-road gasoline emission factors for CO and NOx results in total CO emissions similar to the basin inventory but NOx emissions that are 74% higher than the inventory. The higher NOx emission estimates from on-road gasoline vehicle measurements makes their contribution to the inventory slightly larger than heavy-duty diesel vehicles. We have found LEV I (1994 - 2003) gasoline vehicles are a major source of these on-road emissions and that significant NOx reductions in the South Coast Air Basin are being overlooked by not targeting the high emitters for removal.

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 the article

Bishop, G. A. (2021), Does California’s EMFAC2017 Vehicle Emissions Model Under-predict California Light-duty Gasoline Vehicle NOx Emissions?, J. Air & Waste Manage. Assoc., 71:5, 597-606. DOI: 10.1080/10962247.2020.1869121

Copyright is held by the Air and Waste Management Association