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Monitoring for Air Pollution
Much has been learned in the past few years about
the quality of the air in the Houston-Galveston area. In addition
to the Texas Air Quality Study in 2000 (See Clearing the Air, Air
Quality Basics, Fall 2001), the air is routinely monitored for pollutants
as required by the U.S. EPA. This monitoring takes place at permanent
or temporarily located sites, with mobile monitoring units and with
portable collection devices. Such a large network of air monitors
likely makes the air in the Houston-Galveston area the most monitored
air in the country.
Fixed-site Monitoring
Twenty-seven air-monitoring stations in the eight-county
Houston-Galveston ozone non-attainment area measure for ozone and
other pollutants. However, only five of the eight counties have
air monitors: Brazoria, Chambers, Montgomery, Galveston, and Harris.
The remaining three counties without air monitors are Fort Bend,
Liberty, and Waller. The monitors are operated by three entities:
City of Houston, Texas Commission for Environmental Quality (formerly
TNRCC), and Houston Regional Monitoring Corporation (HRM), a private
agency funded by industry. All 29 sites are networked to a central
computer operated by the Texas Commission on Environmental Quality
(TCEQ) in Austin and data on the pollutants measured can be found
on the TCEQ web site http://www.tnrcc.state.tx.us/cgi-bin/monops.
Most of the monitoring stations measure the concentrations
of two or more of the six criteria air pollutants: ozone, sulfur
dioxide, nitrogen dioxide, lead, particulate matter, and carbon
monoxide. Criteria pollutants have federal standards established
by the EPA based on health and welfare effects. In addition to the
criteria pollutants, some stations measure air toxics and volatile
organic compounds (VOCs) that are necessary for ozone formation.
VOCs are routinely measured in 24-hour samples taken once every
six days. Weather conditions including air temperature, wind velocity
and direction are also measured at most stations.
Twenty-three stations measure particulate matter,
which is made of microscopic particles, both natural and man-made,
that are suspended in the air. Two sizes of particulate matter are
measured: PM10, sometimes called coarse particulate matter and PM
2.5 or fine particulate matter. Some sites collect samples that
are analyzed for particle components.
Temporary Monitoring
Samples are sometimes collected in canisters and analyzed
in response to complaints and later analyzed. In 2001, Houston's
Bureau of Air Quality Control temporarily operated canisters at
Cesar Chavez High School in SE Houston to determine the level of
certain chemicals during differing wind conditions.
Mobile Monitoring
Vans containing air-monitoring equipment can be relocated
to areas not covered by fixed-site monitors. TCEQ has eight mobile
sampling units used for short duration, intensive sampling efforts
around the state. These mobile units can sample for VOCs, sulfur
compounds, or particulate matter depending on the equipment in each
unit. They are usually placed around the facility of interest and
monitoring occurs "around the clock" for up to a week.
Grab Sampling
TCEQ may also collect a short-term canister sample
and analyze the contents as a tool in the investigation process.
Citizens have used a less expensive device constructed from a 5
gallon plastic bucket and containing a special plastic bag to collect
samples in their own back yards.
Recently, citizens teamed up with government agencies through the
Houston-Galveston Citizens Air Monitoring Project to compare the
effectiveness of three air-sampling devices. In the process they
have received valuable data about toxic emissions in their neighborhoods.
If you want to be part of this project, another training is scheduled
for September 28. Watch the website http://www.epa.gov/earth1r6/6lab/hgcamp/hgcamp.htm
for more information.
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