Introduction to Air Quality Modeling

Computer models are used to simulate the meteorological conditions and chemical reactions that contribute to the formation of air pollutants and to predict how air quality in a region will be affected by economic and population growth, and by reducing pollution emissions.

The TCEQ uses state of the art computer models to simulate the meteorological conditions and chemical reactions that contribute to the formation of air pollutants such as ground-level ozone, the most prevalent air pollution in Texas and the nation. The computer models help the TCEQ estimate future air quality in Texas communities that may be violating one or more of the national ambient air quality standards. Modeling results assist agency staff in designing appropriate air-pollution controls and supports commission decision making.

Computer models are vital tools needed to predict how air quality in a region will be affected by economic and population growth and by emissions reductions resulting from federal, state, and local programs. Like all models of complex physical systems, the models used by the TCEQ have some uncertainties, but these models are recognized by EPA as one of the best tools available for developing plans to achieve clean air goals.

There are three critical parts in an air quality modeling process:

The Federal Clean Air Act (FCAA) requires each state to maintain a State Implementation Plan (SIP) which "provides for implementation, maintenance, and enforcement" of the National Ambient Air Quality Standards (NAAQS), for specified air contaminants, including ozone, particulate matter, and regional haze. Because some areas in Texas do not comply with the NAAQS for ozone, the state has amended the Texas SIP to include plans for attaining the NAAQS in each of these areas. These SIP amendments are called "Attainment Demonstrations." The FCAA requires most areas which fail to comply with the NAAQS to use photochemical grid models to demonstrate that the standards will be attained by dates specified in the Act. The EPA may also require states, including those complying with all NAAQS, to include plans for addressing regional air quality issues (such as visibility degradation caused by regional haze) in their SIPs.

Air quality modeling for developing a SIP for ozone involves:

In the past several years, the TCEQ has actively conducted air quality modeling for the following areas:

The TCEQ is also developing modeling files for the following areas under the Rider 8 State and Local Air Quality Planning Program:

Northeast Texas (Tyler-Longview-Marshall area; Gregg, Harrison, Smith, Rusk, and Upshur counties)
San Antonio area (Bexar, Comal, Guadalupe, and Wilson counties)
Austin-Round Rock area (Caldwell, Bastrop, Hays, Travis, and Williamson counties)
Waco area (McLennan County)
Victoria area (Victoria County)
Corpus Christi area (Nueces and San Patricio counties)
El Paso area (El Paso County)

The Air Modeling Data web page provides information on TCEQ air quality modeling projects and links to corresponding data files.

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