Jump to main content or area navigation.

Contact Us

Science Matters

Science Matters Header

EPA Releases Latest Community Multiscale Air Quality Model

New version offers tools for controlling air pollution and studying climate change.

Computer opperator

This fall, EPA scientists released a new version of its groundbreaking Community Multiscale Air Quality modeling system. Earlier versions of this state-of-the-science modeling system (known as “CMAQ”) have been used by EPA and states for more than a decade to design emission control strategies needed to meet and maintain national air quality standards.  The National Weather Service has been using this model for a number of years to produce daily U.S. forecasts for ozone and air quality.

The release of the new version of CMAQ (version 5.0) will give researchers additional tools for studying modern-day air quality issues, including the intercontinental movement of air pollution and how it may affect air quality and climate change.
CMAQ 5.0 includes the latest developments in air chemistry and atmospheric science and will allow CMAQ to take advantage of improvements in computational ability, said EPA scientist Rohit Mathur, who has led the development effort.

“It’s truly a multidisciplinary modeling system, which brings advances in physical, chemical, mathematical, and computational sciences into one framework,” Mathur said.

The CMAQ modeling system unites three kinds of models: meteorological models, emissions models, and an air chemistry-transport model. Using data about land usage, meteorology, and emissions, CMAQ simulates the way pollutants, such as particulate matter and ozone, move through the atmosphere. The system allows states and regulatory agencies to examine the potential impacts of different air quality management strategies to determine the best way to manage pollution in their community, region, or state.

CMAQ’s Framework

“Up till now,” Mathur said, “CMAQ has been run as a two-step model. CMAQ’s driving meteorological models were run in sequence, taking hourly meteorology data, including wind speed and direction, temperature, and solar radiation, and feeding them into an air chemistry model to calculate air quality.”

The new CMAQ 5.0 model includes the capability to use up-to-the minute data in its meteorology and chemical transport models.

“Instead of running the models in sequence as done previously, the meteorology and air chemistry-transport models in CMAQ 5.0 are coupled and synchronized to interact in feedback loops on the fly, thus providing more accurate forecasts that reflect interactions between pollution and weather,” Mathur said.

EPA scientists are currently using CMAQ 5.0 to simulate air quality at smaller, finer spatial resolution settings, such as individual towns and cities. They are also expanding the model’s spatial scale to include the entire northern hemisphere.

The ability to apply the modeling system on the hemispheric scale will allow scientists to better understand the ways that air pollution moves around the globe and provide much-needed information on intercontinental transport for decision makers.

“The atmosphere is vast, and pollutants move from one part of the globe to the other,” Mathur said. “As air quality regulations become stricter, we need to be able to properly account for what is typically called ‘background pollution’—that is, pollution that is not created locally, but is essentially imported from elsewhere into the United States.”

Community Based

An aspect of CMAQ that sets it apart from other air quality models in the world is its community-based development. Instead of keeping the CMAQ model development strictly in-house, EPA has worked with the University of North Carolina at Chapel Hill to create the Community Modeling and Analysis System (CMAS)—an outreach center for air quality modelers and researchers around the world.

 “It takes a large infrastructure to support this kind of system development,” said Kenneth Schere, EPA senior science advisor. “There are very few modeling groups that use the community model of development.”

“CMAQ has become quite a popular system with thousands of users around the world,” Schere added. “Their input has helped us improve the system.  Getting feedback about how the model performs under different conditions has helped us to better focus our research.”

Through the Community Modeling and Analysis System EPA is able to distribute new versions of CMAQ. CMAQ users can also enroll in training courses on the model through the CMAS center and collaborate with other users using the center’s listservs. The center hosts an annual user conference to encourage the exchange of ideas and best practices. About 250 CMAQ users attend each year.

CMAQ’s community-based development has been influencing the expansion of the model’s use around the globe. The model is run by thousands of users in more than 50 countries worldwide. For example, the U.K. uses the model to produce its daily air quality forecasts, and the U.K. Department of Environment, Food, and Rural Affairs—a governmental regulatory agency—recently decided to use the CMAQ model for the development of its national air quality policies.

The model is even making its way to India. Earlier this year, EPA researchers were invited by the Indian government to offer training on the model to Indian researchers so that the government could use the tool to understand pollution in their country.

Training researchers from the Indian government to use the model will also help EPA’s researchers by increasing the amount of world-wide data available in the CMAQ model. This, in turn, will allow researchers to gain a broader picture of the implications of intercontinental transport of air pollution.

Ultimately, CMAQ 5.0 makes the modeling system a more widely-applicable, accurate tool for scientists and policy-makers who deal with air quality. Air and climate scientists will be able to apply CMAQ to new, important research questions, and regulatory bodies will be able to create more cost-effective policies that better protect human health and the environment.

Area Navigation

Jump to main content.