| Περίληψη: | Until recently, organic particulate material was simply classified as either primary or secondary with the primary component being treated in models as nonvolatile and inert. This framework is used to simulate the organic aerosol formation, growth and composition in the eastern United States during the four seasons of the year. The model predictions are evaluated against daily average PM2.5 (particulate matter smaller than 2.5 μm) measurements taken throughout the eastern United States by the Interagency Monitoring of Protected Visual Environments (IMPROVE) and the Speciation Trends Network (STN) monitoring networks. The performance of the model in reproducing organic mass concentrations is average during all four seasons of the year. The agreement between the predicted and observed temporal profiles suggests a reasonable understanding and depiction in the model of the corresponding processes. However, this oversimplified view fails to explain the observed highly oxygenated nature of ambient organic aerosols (OA), the relatively small OA concentration gradients between large urban areas and their surroundings, and the concentrations of OA during periods of high photochemical activity. To address the above issues new primary and secondary organic aerosol modules have been added to a three dimensional chemical transport model (PMCAMx) based on recent smog chamber studies. The new modeling framework is based on the volatility basis-set approach: both primary and secondary organic components are assumed to be semivolatile and photochemically reactive and are distributed in logarithmically spaced volatility bins. The resulting PMCAMx-2008 was applied in Mexico City Metropolitan Area (MCMA) for approximately a week during April of 2003. The model predictions are compared with Aerosol Mass Spectrometry (AMS) observations and their Positive Matrix Factorization (PMF) analysis. The final goal of this work is to provide information to the policy makers regarding the response of fine PM to emission controls. PMCAMx is used to investigate changes in PM2.5 concentrations in response to 50% emissions changes of oxides of nitrogen and anthropogenic volatile organic compounds during July 2001 and January 2002 in the Eastern United States.
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