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 have ozone problems and assist agency staff in
designing appropriate air-pollution controls.
Computer models are necessary 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 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:
Texas ozone nonattainment[1]
areas are:
- Beaumont-Port
Arthur Area - On September 28, 2005, Texas submitted a SIP
revision to EPA demonstrating attainment of the 8-hour ozone
standard by the area's attainment date of 2007.
- Dallas-Fort
Worth Area - On May 23, 2007, Texas submitted a SIP revision to
EPA demonstrating attainment of the 8-hour ozone standard by the
area's attainment date of 2010.
- Houston-Galveston-Brazoria
Area - The TCEQ is currently developing a SIP revision for the
HGB area to show attainment by the area's attainment date of
2018.[2]
- San
Antonio Area - The San Antonio area is currently classified as
Nonattainment-Deferred.
Texas is also developing a SIP revision to address
Regional Haze, in cooperation with the
Central States Regional Air Partnership (CENRAP).
[1] As of June 15, 2005 the
ozone standard of 85 parts/billion (ppb) is based on the daily
maximum eight-hour average concentration. This standard replaced
the previous standard of 125 ppb, which was based on the daily
maximum one-hour concentration.
[2] On June 15, 2007,
Governor Rick Perry formally asked EPA to extend the area's
attainment date from 2009 until 2018.
