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Hazardous Air Pollutants (HAPS)


The increased awareness in recent years of the dangers of toxic air pollutants has caused Congress to design regulatory efforts to control toxic substances in the air. These hazardous air pollutants (HAPS) are air pollutants for which National Ambient Air Quality Standards (NAAQS) do not exist. These pollutants may be expected to cause cancer, developmental effects, reproductive dysfunctions, neurological disorders, heritable gene mutations, or other serious or reversible chronic or acute health effects in humans.

The Clean Air Act of 1970 required the EPA to set National Emission Standards for Hazardous Air Pollutants (NESHAPS). These standards would be required to provide an "ample margin of safety" to human health. However, unlike criteria pollutants, HAPs have no exposure threshold. In other words, there is no minimum amount or duration of exposure to a HAP that can be considered "safe". Because of this, twenty years later only eight pollutants were being regulated as HAPs. NESHAPS were established for asbestos, vinyl chloride, benzene, arsenic, beryllium, mercury, radon, radionuclides other than radon.

The Clean Air Act Amendments (CAA) of 1990 established a new approach for regulating HAPs on the federal level. The amendments revised the Clean Air Act to include 189 compounds as hazardous air pollutants. Recently one pollutant was removed from the list. Standards for these 188 HAPs would be set solely on the basis of available control technology. The current terminology associated with the new standards is "maximum available control technology" or MACT. Sources of HAP emissions subject to MACT standards are categorized as either major or area sources.

Major sources are defined as those sources having the potential to emit ten or more tons per year of any individual HAP or 25 tons per year of any combination of HAPs. The maximum available control technology is determined differently for new and existing sources. MACT for all new sources must be equivalent to the best controlled similar source in a given industry. MACT for existing sources represents the average emission limit achieved by the best-performing 12 percent of the existing sources for which the EPA has information. Existing sources have three years to comply with the applicable MACT standard. MACT standards can be technology based, health based, work practice based, or combinations thereof. Control methods for HAPs are similar to those for the criteria pollutants. The method utilized depends on whether the HAP is a particulate, volatile organic compound (VOC), or a gas.

Area sources are any stationary sources of HAPs that are not major sources; however development of an emissions standard is not required unless an area source category presents a threat to public health or the environment. To date only eight area source categories have been identified and are subject to MACT standards. These include:

  • Asbestos Processing
  • Chromic acid Anodizing
  • Commercial Dry Cleaning Transfer Machines
  • Commercial Dry Cleaning Dry-to-dry Machines
  • Commercial Sterilization Facilities
  • Decorative Chromium Electroplating
  • Hard Chromium electroplating
  • Halogenated Solvent Cleaners