Overview and evaluation of the new Community Multiscale Air Quality (CMAQ) model version 5.1

The Community Multiscale Air Quality (CMAQ) model is a state-of-the-science air quality model that simulates the emission, transport and fate of numerous air pollutants, including ozone and particulate matter. The Atmospheric Modeling and Analysis Division (AMAD) of the U.S. Environmental Protection Agency develops the CMAQ model and releases a new major version of the model every several years (non-major releases can occur more often). In the fall of 2015, the AMAD will release the next major version of the CMAQ model, version 5.1 (CMAQv5.1). This new version of CMAQ will contain numerous updates to the clouds and microphysics, chemistry, and emissions/land-surface characterization in the model, along with bug fixes and code updates to increase the model simulation speed. As part of the model development process and for the release of the new model version, AMAD is performing a comprehensive model evaluation of the new modeling system. The evaluation includes several comparisons, specifically comparisons of the new model and the previous model (CMAQv5.0.2) to an extensive collection of observational data to assess the operational performance of each modeling system using the same inputs; a model-to-model comparison between operational performance the new model and the previous model; and finally a dynamic evaluation to assess the impact that the model changes have on the response of the modeling system to changes in inputs (i.e. emissions). This presentation will summarize the results of these operational and dynamic evaluations, presenting the results of annual 2011 CMAQv5.1 and v5.0.2 simulations. In additional, fine-scale (e.g. 4-km and 1-km) simulations may also be performed using both versions of the model to assess any impact that changes in the new model version have on fine-scale model applications.