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The federal Clean Air Act, as amended in 1990, set out a list of 189 hazardous air pollutants (HAPs). These
are only some of the toxic chemicals being released to air, but many more than the Clean Air Act had been
able to address prior to 1990. EPA was instructed to set "national emissions standards for hazardous air
pollutants" (NESHAPs) specifically for the 189 HAPs. (The 1990 amendment reflected Congress's
frustration with the fact that, in the two decades prior to 1990, standards for only a half-dozen HAPs had
been set.) NESHAPs, however, do not define the maximum allowable concentration of a HAP in outdoor
air. Instead, they are based on EPA's determination of the "maximum achievable control technology" in an
industry. EPA surveys the pollutant releases from an industry, identifies the firms that are doing the best
job of controlling those releases, and then sets so-called "performance standards" for that industry, in the
form of NESHAPs that usually define the rate at which pollutants can be released. Instead of setting
specific limits for each HAP that an industry releases, a NESHAP focuses only on a few priority
chemicals, assuming that control of the few priority chemicals will succeed in controlling other hazardous
air pollutants coming out of the same source. Because they are based on performance capability,
NESHAPs can be different for different industries, even if the chemicals involved are the same.
Eventually, after setting NESHAPs, EPA is supposed to go back and see whether compliance with each
NESHAP is in fact protecting public health with "an ample margin of safety." If not, EPA is then supposed
to set additional standards for different categories of industrial emissions, this time based on health
protection rather than on available technology.
See a list of the
Hazardous Air Pollutants (HAPs)
More information about NESHAPs and the regulation of
Hazardous Air Pollutants (HAPs):
http://www.epa.gov/ttn/uatw/basicfac.html
More information about the Clean Air Act:
http://www.epa.gov/oar/oaqps/peg_caa/pegcaain.html
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