National Emission Standard for Hazardous Air Pollutants (NESHAPs)

The CAA Amendments of 1970 required EPA to identify and list all air pollutants (not already identified as criteria pollutants) that "may reasonably be anticipated to result in an increase in mortality or an increase in serious irreversible or incapacitating reversible illness." For each pollutant identified, EPA was to then promulgate national emissions standards for hazardous air pollutants (NESHAPs) at levels that would ensure the protection of the public health with an ample margin of safety and to prevent any significant and adverse environmental effects, which may reasonably be anticipated, on wildlife, aquatic life, or other natural resources. The approach used by EPA to promulgate NESHAPs was based primarily on health considerations. In other words, EPA has to establish a numerical limit that would protect human health from any adverse effects. The Agency found it very difficult to establish these standards because of the uncertainty in assessing health risk. In the 20 years following enactment of the 1970 legislation, EPA identified only eight pollutants as HAPs and regulated sources of seven of them (asbestos, benzene, beryllium, inorganic arsenic, mercury, radionuclides, and vinyl chloride). (Report of the National Research Council of National Academy of Science, 1994)

The passage of 1990 amendments renewed emphasis on controlling emissions of hazardous air pollutants (HAPs) on the federal level but it changed the approach to regulating HAPs based on the available control technology. A list of 189 compounds was provided by the Congress to be controlled by EPA as HAPs. In 1996 EPA removed one compound from the 189 list (caprolactam); the current list includes 188 compounds. Examples of toxic air pollutants include benzene, which is found in gasoline; perchlorethlyene, which is emitted from some dry cleaning facilities; and methylene chloride, which is used as a solvent and paint stripper by a number of industries. Examples of other listed air toxics include dioxin, asbestos, toluene, and metals such as cadmium, mercury, chromium, and lead compounds. The majority of the HAPs are volatile organic compounds (VOCs).

The original list of the hazardous air pollutants can be found at http://www.epa.gov/ttn/atw/188polls.html

In the first regulatory phase of the HAPs program, the CAA defines two types of emissions standards for promulgation: maximum achievable control technologies (MACTs) and generally available control technologies (GACTs). MACTs are emission standards that achieve "the maximum degree of reduction in emissions of the hazardous air pollutants" taking into consideration the cost of achieving such emission reduction, and any non-air quality health and environmental impacts and energy requirements. MACT is determined differently for new and existing sources of HAPs. For new sources, MACT is equivalent to the best controlled similar source in a given industry. For existing sources, MACT represents the average emission limit achieved by the best performing 12 percent of the existing sources for which EPA has information. GACTs are less stringent emission standards based on the use of more standard technologies and work practices. As of February 2004, EPA had promulgated all the MACT standards required by the 1990 CAA Amendments. EPA developed 96 rules to reduce toxics emissions from over 160 categories of industrial sources. Compared to 1990 baseline emissions, these rules will reduce 1.7 million tons per year of toxics emissions.

In the second regulatory phase of the HAPs program, EPA was instructed to conduct an assessment of and report on the residual risk due to HAPs that is likely to remain after attainment of the MACT and GACT standards. Based on this assessment, EPA may implement additional standards to address any significant remaining, or residual, health or environmental risks. EPA's intent is to implement a residual risk assessment framework that will allow the Agency to be flexible in its decisions while ensuring that public health and the environment are protected. EPA's objectives also include integration of all portions of the federal air toxics program, continuing the partnership with State/local programs in the sharing of data and expertise, and including groups who may be affected by residual risk decisions (e.g., industry, public interest groups) as part of the process.