Plume-in-grid modeling of summer air pollution in Central California

CMAQ-APT (Community Multiscale Air Quality model with “Advanced Plume Treatment”), a state-of-the-science implementation of sub-grid scale reactive plumes in CMAQ, was used to simulate ozone (O3) and nitric acid (HNO3) formation during a 4-day July/August 2000 episode in central California. The top ten NOx emitting plants in the Central California Ozone Study (CCOS) domain were selected for explicit plume treatment. The VOC- vs. NOx-limited nature of the background environment, as determined from air quality data in different parts of the CCOS domain, was used to understand the differences in ozone production and destruction between the APT and base results. Use of the plume-in-grid treatment results in up to 10 ppb less O3 than the base under some O3 production conditions and up to 6 ppb higher O3 under others. Over most of the areas impacted by the top ten NOx emitting plants, the surface HNO3 concentrations in the APT simulation are about 0.1–1 ppb (1–25%) lower than those in the base simulation. The low NOx emissions from point sources in central California explain these results.