Description and evaluation of the Community Multiscale Air Quality (CMAQ) modeling system version 5.1

• Published in: Geoscientific Model Development 2017-01, Vol.10 (4), p.1703-1732
• Main Authors: Appel, K Wyat, Napelenok, Sergey L, Foley, Kristen M, Pye, Havala O T, Hogrefe, Christian, Luecken, Deborah J, Bash, Jesse O, Roselle, Shawn J, Pleim, Jonathan E, Foroutan, Hosein, Hutzell, William T, Pouliot, George A, Sarwar, Golam, Fahey, Kathleen M, Gantt, Brett, Gilliam, Robert C, Heath, Nicholas K, Kang, Daiwen, Mathur, Rohit, Schwede, Donna B, Spero, Tanya L, Wong, David C, Young, Jeffrey O
• Format: Article
• Language: English
• Subjects: Aerosol chemistry; Aerosol concentrations; Aerosols; Air; Air quality; Air quality models; Airborne particulates; Algorithms; Atmospheric chemistry; Atmospheric models; Attenuation; Bias; Carbon; Chemistry; Climatology; Cloud cover; Cloudiness; Clouds; Communities; Computer simulation; Consistency; Correlation; Deposition; Dilution; Drying; Emissions control; Environment models; Environmental protection; Evaluation; Heat; Mixing ratio; Modelling; Multiscale analysis; Nitrogen compounds; Organic carbon; Organic chemicals; Oxides; Ozone; Ozone mixing ratio; Particulate emissions; Particulate matter; Photolysis; Pollutants; Quality; R&D; Research & development; Revisions; Seasonal variation; Seasonal variations; Secondary aerosols; Sensitivity; Simulation; Sulfur dioxide; Summer; Suspended particulate matter; Titration; VOCs; Volatile organic compounds; Weather forecasting; Wet deposition; Winter
• ISSN: 1991-9603; 1991-962X; 1991-959X; 1991-9603; 1991-962X
• DOI: 10.5194/gmd-10-1703-2017

The Community Multiscale Air Quality (CMAQ) model is a comprehensive multipollutant air quality modeling system developed and maintained by the US Environmental Protection Agency's (EPA) Office of Research and Development (ORD). Recently, version 5.1 of the CMAQ model (v5.1) was released to the public, incorporating a large number of science updates and extended capabilities over the previous release version of the model (v5.0.2). These updates include the following: improvements in the meteorological calculations in both CMAQ and the Weather Research and Forecast (WRF) model used to provide meteorological fields to CMAQ, updates to the gas and aerosol chemistry, revisions to the calculations of clouds and photolysis, and improvements to the dry and wet deposition in the model. Sensitivity simulations isolating several of the major updates to the modeling system show that changes to the meteorological calculations result in enhanced afternoon and early evening mixing in the model, periods when the model historically underestimates mixing. This enhanced mixing results in higher ozone (O ) mixing ratios on average due to reduced NO titration, and lower fine particulate matter (PM ) concentrations due to greater dilution of primary pollutants (e.g., elemental and organic carbon). Updates to the clouds and photolysis calculations greatly improve consistency between the WRF and CMAQ models and result in generally higher O mixing ratios, primarily due to reduced cloudiness and attenuation of photolysis in the model. Updates to the aerosol chemistry result in higher secondary organic aerosol (SOA) concentrations in the summer, thereby reducing summertime PM bias (PM is typically underestimated by CMAQ in the summer), while updates to the gas chemistry result in slightly higher O and PM on average in January and July. Overall, the seasonal variation in simulated PM generally improves in CMAQv5.1 (when considering all model updates), as simulated PM concentrations decrease in the winter (when PM is generally overestimated by CMAQ) and increase in the summer (when PM is generally underestimated by CMAQ). Ozone mixing ratios are higher on average with v5.1 vs. v5.0.2, resulting in higher O mean bias, as O tends to be overestimated by CMAQ throughout most of the year (especially at locations where the observed O is low); however, O correlation is largely improved with v5.1. Sensitivity simulations for several hypothetical emission reduction scenarios show that v5.1 te