AAAR 31st Annual Conference
October 8-12, 2012
Hyatt Regency Minneapolis
Minneapolis, Minnesota, USA
Abstract View
Modification of the CMAQ Secondary Organic Aerosol (SOA) Module to Allow Consideration of Activity Coefficients and Water Uptake
MARGUERITE C. MARKS, Abdullah Mahmud, Kelley C. Barsanti, William E. Asher, James F. Pankow, Portland State University
Abstract Number: 597 Working Group: Aerosol Chemistry
Abstract Current regional air quality models such as CMAQ (Community Multiscale Air Quality model) consider that the formation of secondary organic aerosol (SOA) can be calculated by assuming thermodynamic ideality in the organic particulate matter (OPM) phase as well as negligible uptake of water into the OPM phase. Theoretical predictions and model simulations considering non-ideality and water uptake show that the standard model assumptions can lead to large errors in predicted SOA mass, and that the magnitude of these errors is sensitive to the composition of the OPM phase. The SOA module in CMAQ v4.7.1 has been revised in this work to allow consideration of the effects of both non-ideality and water uptake. First, a reasonable specific surrogate structure was assigned to each of the lumped products assumed to be produced by reaction of the different precursor hydrocarbons considered in CMAQ (e.g., isoprene, benzene, and toluene). Second, the CMAQ code was modified to allow iterative calculation (at each point in space and time) of the gas/particle partitioning coefficient for each of the SOA-forming products and for water. Third, model simulations were performed for the Eastern US at a resolution of 12-km x 12-km for three summer months in 2010, under a range of relative humidity conditions. Results will include a comparison of the simulated base-case SOA mass concentrations with those utilizing the updated SOA module, and will be discussed in terms of overall implications for predicted levels of ambient SOA and fine particulate matter.