Additional benefits of federal air quality rules: model estimates of controllable biogenic secondary organic aerosol

Abstract

Atmospheric models that accurately describe the fate and transport of trace species for the right reasons aid in development of effective air quality management strategies that safeguard human health, in particular to mitigate the impacts of fine particulate matter (PM _2.5). Controllable emissions from human activity facilitate formation of biogenic secondary organic aerosol (BSOA) to enhance the atmospheric PM _2.5 burden. Previous modeling with EPA’s Community Multiscale Air Quality (CMAQ) model predicted that anthropogenic primary organic aerosol (POA) emissions had the greatest impact on BSOA. Those experiments included formation processes from semi-volatile partitioning, but not interactions with aerosol liquid water (ALW), a ubiquitous PM constituent that modulates BSOA. We conduct 17 CMAQ summertime simulations with updated chemistry and evaluate changes in predicted BSOA mass due to removal of individual pollutants and source sectors from model inputs for the continental U.S. Among individual sectors, CMAQ predicts that SO ₂ emissions from electricity generating point sources and mobile source NO _x emissions have the largest impact on BSOA. Removal of anthropogenic NO _x, SO ₂ and POA emissions during the simulated summertime period reduces nationally averaged BSOA by 23%, 14% and 8%, and PM _2.5 by 9.2%, 14% and 5.3% respectively. CMAQ-predicted ALW mass concentrations decrease by 10% and 35% in response to removal of NO _x and SO ₂ emissions. This work contributes to the understanding of ancillary benefits of existing and planned Federal NO _x and SO ₂ air quality rules through concurrent reductions in organic PM _2.5 mass.