AAAR 36th Annual Conference October 16 - October 20, 2017 Raleigh Convention Center Raleigh, North Carolina, USA
Abstract View
Investigating the Role of Aromatic Compounds on Anthropogenic Secondary Organic Aerosol in Urban Environments
ALI AKHERATI, Christopher Cappa, Michael Kleeman, Shantanu Jathar, Colorado State University
Abstract Number: 163 Working Group: Regional and Global Air Quality and Climate Modeling
Abstract Aromatic compounds, found in emissions of combustion sources ranging from motor vehicles to biomass burning, photochemically react in the atmosphere to efficiently form secondary organic aerosol (SOA). While a lot is understood about the chemistry of aromatic compounds leading to SOA formation, there are large uncertainties surrounding their relative importance in controlling the atmospheric aerosol burden and air quality in urban environments where numerous sources and processes compete with each other. To study this issue, we performed simulations with a chemical transport model (CTM) to examine the summertime contribution of aromatic compounds to anthropogenic SOA in the South Coast Air Basin (SoCAB). The CTM had a state-of-the-science model (statistical oxidation model) to simulate the chemistry and thermodynamics of SOA and included (i) a semi-volatile and reactive treatment of primary organic aerosol emissions, (ii) emissions of and SOA formation from intermediate-volatility organic compounds, (iii) NOx-dependent, multi-generational aging, and (iv) SOA parameterizations that accounted for artifacts from vapor wall losses in chamber experiments. Most of the aromatic emissions in the SoCAB were from mobile sources with gasoline- and diesel-powered sources accounting for more than 95% of those emissions. Baseline predictions for 2005 of gas-phase aromatic mixing ratios compared exceptionally well with routine measurements made at three SoCAB sites. The same simulations showed that benzene, low-yield, and high-yield aromatics accounted for ~3, 13, and 40% of the anthropogenic SOA formed in the SoCAB; considered together aromatics accounted for ~25% of the total SOA. Of all the processes modeled, the inclusion of the vapor wall loss artifact had the largest influence of doubling the anthropogenic SOA contribution from aromatics. Ongoing work is focused on examining the sensitivity of the aromatic SOA contribution to decadal (2000 to 2010) changes in the emissions and speciation of volatile organic compounds (VOC) from mobile sources and increase in the potential for aromatics to form SOA under lowered NOx concentrations.