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Atmospheric Modeling and Analysis Research

Research In Action

Community Multi-scale Air Quality Model (CMAQ)


The EPA needs detailed information about the concentrations of air pollutants in a given area under almost any imaginable emissions or climate scenario. There is also a need for decision support tools that can be used to design emission control scenarios to help achieve air quality standards.


For more than a decade, the U.S. EPA’s Community Multi-scale Air Quality (CMAQ) Model has been a powerful computational tool used by EPA and states for air quality management. The National Weather Service uses the model to produce daily U.S. forecasts for ozone air quality.  CMAQ is also used by states to assess implementation actions needed to attain National Ambient Air Quality Standards. The system simultaneously models multiple air pollutants, including ozone, particulate matter, and a variety of air toxics to help regulators determine the best air quality management scenarios for their communities, states, and countries.

The CMAQ system includes emission, meteorology, and chemical modeling components.  Research continues in all of these areas to reduce uncertainties in model simulations.  In addition to air quality research and regulation, the CMAQ system is also being developed to address interactions between air pollutant concentrations and climate forcing through 2-way coupling between CMAQ and the Weather Research and Forecast (WRF) model.

Results and Impacts

Since its inception, CMAQ has been designed as a modular system able to incorporate data from related models that have alternate mathematical processes. This capability has allowed for inclusion of new science in the model to address increasingly complex air pollution issues.  Thus, CMAQ has multi-pollutant capabilities to address diverse air quality issues such as photochemical ozone, airborne particulate matter, acid deposition, nutrient deposition and eutrophication, and air toxics.  CMAQ is a truly multi-scale system that has been applied over hemispheric, continental, regional, and urban modeling domains with progressively finer resolution in a series of nested grids.  The CMAQ modeling community includes researchers, regulators, consultants, and forecasters in government, academia, and the private sector with thousands of users worldwide.

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