AIR TOPICS: Ambient Air Quality

AIR TOPICS: Ambient Air Quality

Please visit our Policy Resource Kit page to find out about current actions affecting Ambient Air Quality in your region

Ambient Air Quality Overview

Tribes have historically played an important role in environmental issues including air quality. Tribal citizens are often disproportionately affected by air pollution, while their governments play an increasingly valuable role in controlling and reducing pollution and its adverse health effects. The EPA regulates ambient air quality through the Clean Air Act. Tribes and states are co-regulators. NTAA partners with Tribes to address the many issues that impact Outdoor Air Quality. These include air toxins like lead and mercury, particulate matter and regional haze.

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National Ambient Air Quality Standards

The Clean Air Act requires EPA to set National Ambient Air Quality Standards for pollutants that are common in outdoor air, considered harmful to public health and the environment, and that come from numerous and diverse sources.  

EPA focuses on six “criteria” pollutants in outdoor air. They include carbon monoxide, lead, ground-level ozone, nitrogen dioxide, particulate matter, and sulfur dioxide. These pollutants are found all over the U.S. The standards for each pollutant are reviewed every five years.

TABLE: National Ambient Air Quality Standards Table

Nitrogen Oxides

Nitrogen Dioxide (NO2) is one of a group of highly reactive gases known as oxides of nitrogen or nitrogen oxides (NOx). Other nitrogen oxides include nitrous acid and nitric acid. NO2 is used as the indicator for the larger group.

NO2 forms quickly from emissions from cars, trucks and buses, power plants, and off-road equipment. In addition to contributing to the formation of ground-level ozone, and fine particle pollution, NO2 is linked with a number of adverse effects on the respiratory system.

EPA first set standards for NO2 in 1971, setting both a primary standard (to protect health) and a secondary standard (to protect the public welfare) at 0.053 parts per million (53 ppb), averaged annually. The Agency has reviewed the standards twice since that time, but chose not to revise the standards at the conclusion of each review. All areas in the U.S. meet the current (1971) NO2 standards.


Lead (Pb) is a metal found naturally in the environment as well as in manufactured products. The major sources of lead emissions have historically been motor vehicles (such as cars and trucks) and industrial sources. As a result of EPA’s regulatory efforts to remove lead from gasoline, emissions of lead from the transportation sector dramatically declined by 95 percent between 1980 and 1999, and levels of lead in the air decreased by 94 percent between 1980 and 1999. 

Today, the highest levels of lead in air are usually found near lead smelters. Other stationary sources are waste incinerators, utilities, and lead-acid battery manufacturers.

Particulate Matter

“Particulate matter,” also known as particle pollution or PM, is a complex mixture of extremely small particles and liquid droplets. Particle pollution is made up of a number of components, including acids (such as nitrates and sulfates), organic chemicals, metals, and soil or dust particles.

The size of particles is directly linked to their potential for causing health problems. EPA is concerned about particles that are 10 micrometers in diameter or smaller because those are the particles that generally pass through the throat and nose and enter the lungs. Once inhaled, these particles can affect the heart and lungs and cause serious health effects. EPA groups particle pollution into two categories:

“Inhalable coarse particles,” such as those found near roadways and dusty industries, are larger than 2.5 micrometers and smaller than 10 micrometers in diameter.

“Fine particles,” such as those found in smoke and haze, are 2.5 micrometers in diameter and smaller. These particles can be directly emitted from sources such as forest fires, or they can form when gases emitted from power plants, industries and automobiles react in the air.

Carbon Monoxide

CO is a colorless, odorless gas that can be harmful when inhaled in large amounts. CO is released when something is burned. The greatest sources of CO in outdoor air are cars, trucks and other vehicles or machinery that burn fossil fuels. 

Breathing air with a high concentration of CO reduces the amount of oxygen that can be transported in the blood stream to critical organs like the heart and brain.

At very high levels, CO can cause dizziness, confusion, unconsciousness and death.

Very high levels of CO are not likely to occur outdoors. However, when CO levels are elevated outdoors, they can be of particular concern for people with some types of heart disease. They are especially vulnerable to the effects of CO when exercising or under increased stress. In these situations, short-term exposure to elevated CO may result in reduced oxygen to the heart accompanied by chest pain also known as angina.

Ground Level Ozone

Ozone can be good” or bad” for health and the environment depending on where its found in the atmosphere. Stratospheric ozone is good” because it protects living things from ultraviolet radiation from the sun. Ground-level ozone, however, is bad” because it can trigger a variety of health problems, particularly for children, the elderly, and people of all ages who have lung diseases such as asthma.

Ground-level ozone is created when pollutants emitted by cars, power plants, industrial boilers, refineries, chemical plants, and other sources react in the presence of sunlight.

Ozone is most likely to reach unhealthy levels on hot sunny days in urban environments, but can still reach high levels during colder months. Ozone can also be transported long distances by wind, so even rural areas can experience high ozone levels. Ozone can cause the muscles in the airways to constrict, leading to wheezing and shortness of breath. These effects have been found even in healthy people, but can be more serious in people with lung diseases such as asthma.

Sulfur Dioxide SO2

EPAs national ambient air quality standards for SO2 are designed to protect against exposure to the entire group of sulfur oxides (SOx).  SO2 is the component of greatest concern and is used as the indicator for the larger group. SO2 is colorless, but has a pungent odor like that of a just struck match.

The largest source of SO2 in the atmosphere is the burning of fossil fuels by power plants and other industrial facilities. Smaller sources of SO2 emissions include: industrial processes such as extracting metal from ore; natural sources such as volcanoes; and locomotives, ships and other vehicles and heavy equipment that burn fuel with a high sulfur content. 

Short-term exposures to SO2 can harm the human respiratory system and make breathing difficult. People with asthma, particularly children, are sensitive to these effects. At high concentrations, gaseous SOx can harm trees and plants by damaging foliage and decreasing growth. They can also contribute to acid rain. SO2 and other sulfur oxides can react with other compounds in the atmosphere to form fine particles that reduce visibility (haze) in parts of the United States, including many of our treasured national parks and wilderness areas.  

Mercury and Air Toxic Standards (MATS)

In 2012, EPA issued the first regulations to control hazardous air pollution (HAP) such as mercury and arsenic from coal-burning and oil-burning power plants with a capacity of 25 megawatts or greater. Known as the Mercury and Air Toxic Standards, power plant operators were given four years to comply. By one study, emissions of mercury dropped 81% by 2017.

The energy industry and some states challenged the rules in court. One case, Michigan vs EPA, was heard by the US Supreme Court. In 2015 the court ruled the EPA failed to properly weigh the costs of the new regulations against the health benefits to society.

In 2018, EPA issued a new ruling that greatly reduced the estimated health benefits and determined it was no longer “appropriate and necessary” to regulate hazardous air pollutants under section 112 of the Clean Air Act.

Other Toxic Substances


Mercury is a naturally-occurring element found in rock in the earth’s crust, including in deposits of coal. It exists in several forms. For example, pure mercury is a liquid metal that is traditionally used to make products like thermometers, switches, and some light bulbs.

Emissions from coal burning power plants are the biggest source of mercury in outdoor air. Airborne mercury eventually settles into water, or on land where it may be washed into lakes, streams and rivers. People are most likely to be exposed to mercury by eating fish and shellfish with high levels of methylmercury, a highly toxic form of mercury. Other sources include dental fillings and some jewelry. Mercury exposure at high levels can harm the brain, heart, kidneys, lungs, and immune system of people of all ages.

Mercury consumption is a health concern among Tribes whose traditional diets include large amounts of fish, waterfowl, medicinal plants, moose and other land animals. Such diets have not been adequately considered by the EPA in the process of addressing emissions standards for mercury. For example, in developing its recent rule for mercury emissions from power plants, EPA considered two segments of the population to be relevant to its analysis: recreational anglers, and “high level” consumers such as some Native American and other ethnic populations. 

In calculating the risk to these groups, USEPA used maximum fish consumption levels of 25 g/day for anglers and 170 g/day for high consumers. However, even this “high level” number may be far from adequate for some Tribal populations. For example, a survey of Great Lakes area Tribes produced a range of 189.6 to 393.8 g/day, and the Minnesota Chippewa Tribe has adopted 227 g/day as its treaty protected subsistence quantity. 

Many Tribes are in the midst of assessments of mercury levels in their water, fish, and wildlife. In general, however, there is marked absence of mercury deposition data in the western U.S., where the majority of the Tribal land base exists. Because dry deposition monitoring techniques are not as developed as wet deposition techniques, data is particularly lacking in the southwest, where dry deposition predominates. Acquiring more deposition and health effects data is a priority for Tribes in the years to come.


Like Mercury, power plant emissions of arsenic are regulated by the EPA under the MATS rule. EPA says power plants are responsible for 62% of arsenic air pollution in the US.

Arsenic occurs naturally in soil and minerals and it therefore may enter the air, water, and land from wind-blown dust and may get into water from runoff and leaching. Volcanic eruptions are another source of arsenic. Arsenic is associated with ores containing metals, such as copper and lead. Arsenic may enter the environment during the mining and smelting of these ores.

Breathing high levels of inorganic arsenic can give you a sore throat or irritated lungs or may cause a darkening of the skin and the appearance of small “corns” or “warts” on the palms, soles, and torso. Breathing inorganic arsenic can also increase the risk of lung cancer. The Department of Health and Human Services (DHHS) and the EPA have determined that inorganic arsenic is a known human carcinogen.


Benzene is a widely used chemical formed from both natural processes and human activities. Breathing benzene can cause drowsiness, dizziness, and unconsciousness; long-term benzene exposure causes effects on the bone marrow and can cause anemia and leukemia.

Industrial processes are the main sources of benzene in the environment. Benzene levels in the air can be elevated by emissions from burning coal and oil, benzene waste and storage operations, motor vehicle exhaust, and evaporation from gasoline service stations. Tobacco smoke is another source of benzene in air, particularly indoors.

Tribal New Source Review (NSR)

Title I of the Clean Air Act (CAA) requires that the New Source Review (NSR) program be established to protect public health and welfare, national parks, and wilderness areas as new sources of pollution are built or existing sources modified. The program is designed to ensure that new sources of pollution are constructed to be as clean as possible, recognizing that facility construction is typically the most economical time to incorporate state-of-the-art pollution prevention practices or air pollution control technologies. 

In 2011, the EPA filled a regulatory gap with the development of the Tribal Minor New Source Review. The final rule outlines preconstruction permitting of air pollution control requirements for industrial facilities located in Indian Country. 

The Tribal Minor NSR program provides three options for obtaining permits:

  • Site-Specific Permits: includes case-by-case determinations of the source emission limits as well as any control technology requirements
  • General Permits: permits that have been developed for a number of similar equipment types or facilities to simplify the permit issuance process for facilities; or
  • Synthetic Minor Permits: applies to a facility that has the potential to emit pollutants in amounts that are at or above major source thresholds, but has voluntarily accepted emission limits so that its potential emissions are below those thresholds, allowing the facility to avoid more stringent major NSR requirements of the Clean Air Act.
Regional Haze

In 1999, the EPA announced a major effort to improve air quality in national parks and wilderness areas. The Regional Haze Rule calls for state and federal agencies to work together to improve visibility in 156 national parks and wilderness areas such as the Grand Canyon, Yosemite, the Great Smokies and Shenandoah.

The rule requires the states, in coordination with the EPA, the National Park Service, U.S. Fish and Wildlife Service, the U.S. Forest Service, and other interested parties, to develop and implement air quality protection plans to reduce the pollution that causes visibility impairment. The first State plans for regional haze were due in December 2007. States, tribes, and five multi-jurisdictional regional planning organizations worked together to develop the technical basis for these plans. Comprehensive periodic revisions to these initial plans are currently due in 2021, 2028, and every 10 years thereafter.

NTAA submitted early comments in response to EPA’s request for comments for Tracking Visibility Progress in the Regional Haze Rule that focus on the Reasonable Progress Framework on Controllable Emissions that contribute to Regional Haze. In addition, comments were submitted by NTAA regarding the proposed delay of the current state implementation plan (SIP) submission deadlines, the timing and format of progress reports, limiting requirements for reasonably attributable visibility impairment (RAVI) while expanding the number of states that would be subject to Federal Land Management (FLM) RAVI certifications, and consultation with Indian Tribes concerning the RHR and associated activities. EPA will be drafting a guidance document in the coming months and issue that guidance document for further review in the new year.

Ambient Air Quality Resources

Status of Tribal Air Report (STAR)

Each year, NTAA produces an annual Status of Tribal Air Report (STAR) to Tribal Nations, the U.S. Environmental Protection Agency (EPA), and to other federal agencies and interested parties. The report provides a national overview of Tribal Air Quality Programs for the current administration; presents the successes, challenges, and priorities from a regional perspective of managing air quality; and tells stories of management of air quality from across Indian Country.

NTAA: 2019 Status of Tribal Air Report


Northern Arizona University’s Institute for Tribal Environmental Professionals (ITEP) also provides extensive online and other training resources for anyone who wants to study air quality issues in-depth. Follow these links to learn more.


NTAA partners with others to advance air quality including:
American Lung Association
National Association of Clean Air Agencies
Association of Air Pollution Control Agencies

EPA Resources

EPA’s Office of Air and Radiation (OAR)

EPA’s Office of Air and Radiation (OAR) is responsible for administering the Clean Air Act as well as other environmental laws. OAR’s national programs provide important air quality and health benefits to tribal communities while assisting the efforts of tribal governments. Tribes have made tremendous progress with air quality management, but there is still significant need for tribal air quality management programs and climate change plans to be developed, refined, and supported.


The EPA reports the Air Quality Index (AQI) in real time for more than 400 locations in the US. The AQI tells us how clean or polluted outdoor air is, along with associated health effects that may be of concern. The AQI translates air quality data into numbers and colors that help people understand when to take action to protect their health. Visit the EPA site to stay informed of the latest IA issues.

Funding Opportunities

In 1992, Congress passed the Indian Environmental General Assistance Program Act. This act authorized EPA to provide General Assistance Program (GAP) grants to federally recognized tribes and tribal consortia for planning, developing and establishing environmental protection programs in Indian country, and for developing and implementing solid and hazardous waste programs on tribal lands.

EPA: Indian Environmental General Assistance Program (GAP)

Multipurpose Grants to States and Tribes is a program which provides funding to states, tribes, and territories for high priority activities that complement programs under established environmental statutes.

EPA: Multipurpose Grants to States and Tribes

NAU/ITEP Lead: Andy Bessler, NTAA Project Director