AAAR 31st Annual Conference
October 8-12, 2012
Hyatt Regency Minneapolis
Minneapolis, Minnesota, USA
Abstract View
Chemically-Constrained CMAQ Evaluation of Organic Compounds with CALNEX Field Measurements
ANNMARIE CARLTON, Kirk Baker, Tadeusz Kleindienst, John Offenberg, Mohammed Jaoui, Rutgers University
Abstract Number: 678 Working Group: Aerosol Chemistry
Abstract CMAQ predictions of gas- and aerosol-phase organic compounds are evaluated with measurements at two locations, Pasadena and Bakersfield California, USA during the CalNex campaign. Analysis of secondary organic aerosol (SOA) tracers indicates that species in CA are chemically different from previous measurements in the Eastern U.S. Specifically, methyltetrols while routinely the predominant SOA species measured in the Eastern U.S. are do not exhibit similar dominance during CalNex. Individual SOA species mass concentrations derived from xylenes, toluene, isoprene and monoterpenes are underpredicted relative to measurements, even though there is no bias or an overprediction for the VOC precursors. Sesquiterpene SOA tracer concentrations are below method detection limits (MDLs) throughout CalNex at both locations, while the model predicts that the SOA species is present. CMAQ's chemically specific organic carbon predictions are presented in the context of 1- and 2-dimensional volatility distributions. There are gaps and inconsistencies in the model’s saturation vapor pressures (C*) and oxygen-to-carbon ratios (O:C) for organic aerosol when compared to theory and observations. The findings suggest that model development focused on improving representation of organic aerosol with saturation vapor pressures -3 <= log10C* <= -1 and O:C > 0.2 would likely be most efficient for reconciling model predictions with atmospheric measurements.