Improved Spatial Resolution in Modeling of Nitrogen Oxide Concentrations in the Los Angeles Basin
Katelyn A. Yu, Meng Li, Colin Harkins, Jian He, Qindan Zhu, Bert Verreyken, Rebecca H. Schwantes, R. C. Cohen, Brian McDonald, Robert A. Harley
Abstract
High Resolution Image Download MS PowerPoint Slide The extent to which emission control technologies and policies have reduced anthropogenic NO x emissions from motor vehicles is large but uncertain. We evaluate a fuel-based emission inventory for southern California during the June 2021 period, coinciding with the Re-Evaluating the Chemistry of Air Pollutants in CAlifornia (RECAP-CA) field campaign. A modified version of the Fuel-based Inventory of Vehicle Emissions (FIVE) is presented, incorporating 1.3 km resolution gridding and a new light-/medium-duty diesel vehicle category. NO x concentrations and weekday–weekend differences were predicted using the WRF-Chem model and evaluated using satellite and aircraft observations. Model performance was similar on weekdays and weekends, indicating appropriate day-of-week scaling of NO x emissions and a reasonable distribution of emissions by sector. Large observed weekend decreases in NO x are mainly due to changes in on-road vehicle emissions. The inventory presented in this study suggests that on-road vehicles were responsible for 55–72% of the NO x emissions in the South Coast Air Basin, compared to the corresponding fraction (43%) in the planning inventory from the South Coast Air Quality Management District. This fuel-based inventory suggests on-road NO x emissions that are 1.5 ± 0.4, 2.8 ± 0.6, and 1.3 ± 0.7 times the reference EMFAC model estimates for on-road gasoline, light- and medium-duty diesel, and heavy-duty diesel, respectively.