Implementation and initial application of the near-explicit Master Chemical Mechanism in the 3D Community Multiscale Air Quality (CMAQ) model
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A modified Master Chemical Mechanism (MCM) with 4642 species and 13,566 reactions was incorporated into the 3D Community Multiscale Air Quality (CMAQ) model (CMAQ-MCM) and applied to study a three-week high ozone episode in Southeast Texas during the Texas Air Quality Study 2000 (TexAQS 2000). The 3D CMAQ-MCM model successfully reproduced the observed ozone concentrations throughout the Southeast Texas region, with model performance similar to that of the standard SAPRC07 mechanism. The CMAQ-MCM has been used to evaluate the VOC emission inventory by directly simulating the concentrations of a large number of VOCs. The simulated 1-h and 24-h average concentrations of major ozone precursor VOCs show that most of the alkanes and alkenes are universally lower than the observed values by a factor of 2-5. The under-prediction of ethane and propane is more significant, by a factor of approximately 5-10. Major aromatic compounds generally agree better with observation within a factor of 2. At the Clinton Drive site, most of the under-predictions occur in the afternoon when industrial facilities are in the immediate upwind direction. The observed concentrations of a number of the under-predicted species show strong correlations with temperature, suggesting that evaporative emissions are underestimated in the emission inventory. 2011 Elsevier Ltd.
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