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Outdoor Air:
Hazardous Air Pollutants (HAPs)
The 1990 Clean Air Act named 189 chemicals, metals and particulates as
Hazardous Air Pollutants, commonly referred to as HAPs. These pollutants are
known to increase the risk of developing cancer, immune and neurological damage,
reproductive and endocrine disorders, and birth defects in children. For this
reason, federal regulations of these substances are more rigorous.
Benzene, toluene, vinyl chloride, perchloroethylene, arsenic, mercury,
diesel particulates and various pesticides are included on the list. For a
complete list of the HAPs, along with information about the known health effects
associated with each, go to the US EPA's
Health
Effects Notebook for Hazardous Air Pollutants.
Because of the concentration of petrochemical industry
 in
the Houston region, combined with the area's reliance on automobiles and trucks
for transportation, most research suggests that the area has higher levels of
HAPs than most other urban areas. For example, the levels of 1,3-butadiene
measured in the air are up to six times higher than the levels measured in the
Los Angeles area.
To obtain hourly and annual averages of selected chemicals sampled at
monitors in the Houston region, the Texas Commission on Environmental Quality's
Air Pollution Data Collected by Automated Gas Chromatographs is very useful.
Additionally, the U.S. Environmental Protection Agency's
Monitor Values Report - Hazardous Air Pollutants
provides summaries of monitor data collected since 1995 for numerous hazardous air pollutants in Texas and other states.
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