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CMAQ is an acronym for the Community Multi-scale Air Quality Model,[1][2] a sophisticated atmospheric dispersion model developed by the US EPA to address regional air pollution problems. (For example, a multi-state area where ozone or fine particulate levels exceed the US health standards.) In addition to simulating the emission, advection, diffusion, and deposition of air pollutants, CMAQ treats a wide array of chemical reactions that occur throughout the lower atmosphere. For example, ozone forms in the atmosphere when nitrogen oxides interact with volatile organic compounds in the presence of sunlight. Ammonium sulfate is formed in fine particulate matter when sulfuric acid (formed largely in cloud water) interacts with gas-phase ammonia.[3] Meteorological conditions such as subsidence inversions, decrease the amount fresh air available for dilution of air emissions, and increase the rate of production of secondary air pollutants. CMAQ has the capability to accurately predict air pollution concentrations resulting from secondary formation. Like any air dispersion model, CMAQ inputs air pollutant emissions and meteorological data and outputs air pollutant concentrations and deposited totals. Its particular strength is in assessing the efficacy of regional emissions control strategies in reducing regional air pollution levels.
CMAQ may also refer to the Congestion Mitigation and Air Quality Improvement Program, a program of the United States Department of Transportation.[4]

^ “Community Multi-scale Air Quality Model | Research in Action | US EPA”. 2010-11-17. Retrieved 2015-06-03. 
^ “Community Modeling and Analysis (CMAS) – CMAQ”. 2014-10-24. Retrieved 2015-06-03. 
^ “The Impact of Nonlocal Ammonia on Submicron Particulate Matter and Visibility Degradation in Urban Shanghai”. Retrieved 2015-06-03. 
^ “Congestion Mitigation and Air Quality Improvement (CMAQ) Program”. U.S. Department of Transportation. Retrieved 4 November 2015. 

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