Department of
Environmental Quality

Toxic air pollutants (TAPs) are those pollutants that are known or suspected to cause cancer or other serious health effects, such as reproductive effects or birth defects, or to cause adverse environmental effects.

Air toxics are regulated by both state and federal programs. Idaho's Air Toxics Program regulates approximately 350 toxic air pollutants (TAPs), while EPA's federal program regulates 188 hazardous air pollutants (HAPs). Both TAPs and HAPs are referred to as air toxics.

Idaho's TAP program preceded the federal program. Some areas overlap in the state and federal programs.

Idaho's TAP Program

Idaho's TAP Program is a stand-alone risk-based program that regulates approximately 350 pollutants determined by their nature to be toxic to human or animal life or vegetation. Idaho's regulations prohibit emission of these contaminants alone or in combination with other contaminants in amounts that would injure or unreasonably affect human or animal life or vegetation.

TAP emission limits from industrial sources are limited by acceptable ambient concentrations (AACs) for carcinogenic and non-carcinogenic pollutants and by screening emission levels (ELs) for non-carcinogens.

AACs are the maximum concentration levels allowed in the outside air from a pollution source or sources under construction or modification. Compliance is often verified by computer modeling or ambient air sampling. AACs for non-carcinogens are 24-hour averages. These levels can be found in IDAPA 58.01.01.585. Acceptable ambient concentrations for carcinogens (AACCs) are annual averages. These levels can be found in IDAPA 58.01.01.586.

ELs are stack-based emission levels based on pounds of each pollutant emitted per hour. Compliance is often verified by engineering calculations, computer modeling, or stack sampling. Emission levels for non-carcinogens can be found in IDAPA 58.01.01.585, while emission levels for carcinogens can be found in IDAPA 58.01.01.586.

Relationship to the Federal HAP Program

If a new or modified source emits an air toxic that is regulated by both Idaho's program and EPA's HAP program, then the source is exempt from the state program for the specific pollutant regulated by the federal standard. If the source emits additional TAPs not covered under the applicable federal standard, then the source is subject to the state regulations for those pollutants. Learn more.

Chemical Accidental Release and Prevention: Clean Air Act Section 112(r)

Chemical accidents can occur at businesses of any size. Many small businesses handle ammonia, chlorine, and other chemicals that could pose a risk to the surrounding community if an accident were to occur. Section 112(r) of the 1990 Clean Air Act Amendments prescribes a series of requirements aimed at preventing and minimizing the consequences of chemical accidental releases. Learn more.

National-Scale Air Toxics Assessment (NATA)

The NATA is an ongoing comprehensive evaluation by EPA of air toxics in the U.S. It is designed to help EPA, state, local, and tribal governments, and the public better understand the extent of the air toxics problem in the U.S. and to help focus future efforts to reduce air toxics and associated health impacts. The assessment includes four steps:

1. Inventory air toxics emissions.
2. Estimate annual average outdoor air toxics concentrations.
3. Estimate exposure concentrations (what people are estimated to breathe).
4. Characterize potential public health risks.

Information gained by the NATA will help EPA accomplish the following:

• Identify air toxics of greatest potential concern.
• Characterize the relative contributions to air toxics concentrations and population exposures of different types of air toxics emissions sources.
• Set priorities for the collection of additional air toxics data to improve estimates of air toxics concentrations and their potential public health impacts. Important additional data collection activities include upgraded emission inventory information, ambient air toxics monitoring, and information on adverse effects to health and the environment.
• Establish a baseline to track trends over time in modeled ambient concentrations of air toxics.
• Establish a baseline for measuring progress toward meeting goals for inhalation risk reduction from ambient air toxics.

EPA has released two phases of the NATA, which evaluated 32 high priority TAPs. The first phase includes estimated air toxics emissions and outdoor air concentrations. The second phase provides estimates of human exposure to these pollutants and associated health risks. The NATA will help DEQ target areas of the state where more detailed information and air toxics reduction strategies are needed.

EPA's Urban Air Toxics Program

Under EPA's Urban Air Toxics Program, states will be required to assess local air quality data to identify urban areas where air toxics emissions need to be reduced. States also must devise a process for developing and implementing strategies to reduce health risks from air toxics, provide an opportunity for public participation and review, and develop tools to evaluate whether emissions have been reduced.

The Integrated Urban Air Toxics Strategy

The Integrated Urban Air Toxics Strategy is a framework for addressing air toxics emissions in urban areas. The strategy defines a county as "urban" if it includes a metropolitan statistical area with a population greater than 250,000 or the U.S. Census Bureau has designated more than 50% of the population as "urban." (Note: This definition does not necessarily apply for regulatory or implementation purposes.)

Under the national air toxics program, EPA has and will continue to develop a number of national standards for stationary and mobile sources to improve air quality in urban and rural areas. The strategy complements these efforts by focusing on achieving even further reductions in air toxics emissions in urban areas. The strategy outlines actions to reduce emissions of air toxics, as well as assessment activities to improve EPA's understanding of the health and environmental risks of air toxics in urban areas.

The strategy includes a list of 33 urban air toxics that pose the greatest potential health threat in urban areas and a list of area sources responsible for a substantial portion of these air toxics emissions. This list includes 29 area source categories, 13 of which are new and 16 are under development or already subject to standards.

• List of 33 Urban Air Toxics