Realizing additional benefits of federal air quality rules: particle water chemistry and biogenic secondary organic aerosol controllable fractions

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 deleterious impacts of fine particulate matter (PM2.5). Controllable emissions from human activity facilitate formation of biogenic secondary organic aerosol (BSOA) to enhance the atmospheric fine particulate matter (PM2.5) burden. Previous modeling with EPA’s Community Multiscale Air Quality (CMAQ) predicted that primary organic aerosol (POA) emissions are the most consequential: those model experiments included formation processes from semi-volatile partitioning, but not recently discovered condensed phase organic chemistry or consideration of aerosol liquid water (ALW). We conduct 17 CMAQ simulations with this updated chemistry and evaluate changes in predicted BSOA mass due to removal of individual pollutants and source sectors from model inputs for July 2013 for the continental U.S. For individual sectors CMAQ predicts that mobile source NOx emissions have the largest impact on biogenic SOA, followed by SO2 from electricity generating point sources. Removal of anthropogenic NOx, SO2 and POA emissions reduces nationally averaged BSOA by 23%, 14% and 8%, respectively. These results contrast sharply with previous BSOA controllability estimates. Predicted ALW mass concentration response to anthropogenic emissions from specific source sectors is quantitatively evaluated for the first time with CMAQ and found to decrease by 10% and 35% in response to removal of controllable NOx and SO2 emissions, respectively. This work suggests ancillary benefits of existing and planned Federal NOx and SO2 air quality rules through concurrent reductions in organic PM2.5 mass.

Speaker: Ann Marie Carlton, UC Irvine