Abstract Number: 695 Working Group: Carbonaceous Aerosols in the Atmosphere
Abstract Ambient fine particulate matter (PM2.5) in the Houston area is influenced by diverse sources including natural sources, motor vehicles, petrochemical industry, marine vessels, and other anthropogenic sources. Organic aerosol (OA) frequently makes an important contribution to Houston’s PM2.5. OA has been traditionally classified as primary or secondary OA (POA or SOA): POA is directly emitted into atmosphere as particles while SOA is formed when hydrocarbon precursors undergo one or more chemical transformations in the gas phase, forming less volatile compounds that partition to the particle phase. The gas-phase precursors of SOA are classified (in decreasing order of volatility) as volatile organic compounds (VOC), intermediate volatility organic compounds (IVOC) and semivolatile organic compounds (SVOC). Early SOA modeling focused on the VOC precursors but more recent modeling using a volatility basis set (VBS) has shown that SOA formation from IVOC precursors is important. Current emission inventory methods essentially omit IVOC emissions making it necessary to add IVOCs to modeling inventories using approximations. In this study, a photochemical grid model is applied to simulate OA formation in the Houston region during the 2013 DISCOVER-AQ campaign. SOA formation from both VOC and IVOC is modeled using a recently developed 1.5-dimensional VBS model. IVOC emissions are added to the TCEQ's latest 2013 emission inventory using IVOC fractions determined from smog chamber studies. The model results are evaluated against detailed ambient OA measurement data collected during DISCOVER-AQ.