Dominance of Wildfires Impact on Air Quality Exceedances during the 2020
Record-Breaking Wildfire Season in the United States
Abstract
The western United States experienced a record-breaking wildfire season
in 2020. This study quantifies the contribution of wildfire emissions to
the exceedances of health-based National Ambient Air Quality Standard
(NAAQS) for fine particles (PM2.5) by comparing two CMAQ
simulations, with and without wildfire emissions. During August to
October 2020, western wildfires contributed 23% of surface
PM2.5 in the contiguous US (CONUS), with a larger
contribution in Pacific Coast (43%) and Mountain Region (42%).
Consequently, wildfires were the primary contributor to the 3,720
observed exceedances. The wildfire influence peaked on September
14th, 2020, when 273 exceedances were recorded and
wildfire emissions contributed 41%, 81%, and 72% to surface
PM2.5 concentrations in the CONUS, Pacific Coast, and
Mountain regions, respectively. Our finding highlights the predominating
influence of wildfires on air quality, and potentially human health,
that is expected to grow with increasing fire activities, while
anthropogenic emissions decrease.