Kiera Jefferson
The Clean Air Act requires the Environmental Protection Agency (EPA) to set National Ambient Air Quality Standards (NAAQS) for six principal pollutants, or 'criteria' pollutants, that are harmful to public health and the environment. These pollutants are typically emitted from sources in industry, mining, transportation, electricity generation, and agriculture and are often the products of fossil fuel combustion or industrial processes. The six criteria pollutants are ozone (O3), atmospheric particulate matter (PM2.5/PM10), lead (Pb), carbon monoxide (CO), sulfur oxides (SOx), and nitrogen oxides (NOx). While the EPA has established standards for these six pollutants, it is important to note that other chemicals and pollutants not covered by the NAAQS may still be regulated under different frameworks, such as the National Emissions Standards for Hazardous Air Pollutants.
| Characteristics | Values |
|---|---|
| Number of pollutants | 6 |
| Type of standards | Primary and secondary |
| Purpose | Protect public health and the environment |
| Pollutants | Ozone (O3), atmospheric particulate matter (PM2.5/PM10), lead (Pb), carbon monoxide (CO), sulfur oxides (SOx), and nitrogen oxides (NOx) |
| Other pollutants covered | Nitric oxide (NO), nitrous oxide (N2O), and nitrogen dioxide (NO2) |
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What You'll Learn
The Clean Air Act
To achieve the NAAQS goals, the Clean Air Act directs states to develop state implementation plans (SIPs) applicable to industrial sources within their borders. The Act also establishes a risk-based program for emissions from major sources and certain area sources. "Major sources" are defined as stationary sources emitting or capable of emitting 10 tons or more of a hazardous pollutant annually. The EPA is mandated to set emission standards, known as "maximum achievable control technology" (MACT) standards, for these major sources to ensure the highest possible reduction in hazardous air pollutant emissions.
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Primary Standards
The Clean Air Act requires the Environmental Protection Agency (EPA) to set National Ambient Air Quality Standards (NAAQS) for six principal pollutants, or "criteria pollutants", that are common in outdoor air and harmful to public health and the environment. These six criteria pollutants are:
- Ozone (O3)
- Atmospheric particulate matter (PM2.5/PM10)
- Lead (Pb)
- Carbon monoxide (CO)
- Sulfur oxides (SOx)
- Nitrogen oxides (NOx)
The EPA is required to periodically review and revise the NAAQS for each pollutant, taking into account the latest scientific knowledge. These reviews occur every five years and are conducted by a Clean Air Scientific Advisory Committee (CASAC) consisting of seven members appointed by the EPA administrator.
The primary standards for the other criteria pollutants are also regularly reviewed and revised as necessary to ensure the protection of public health. These standards play a crucial role in safeguarding the well-being of individuals, especially those who are more vulnerable to the harmful effects of air pollution.
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Secondary Standards
The Clean Air Act requires the Environmental Protection Agency (EPA) to set National Ambient Air Quality Standards (NAAQS) for six principal pollutants, or "'criteria pollutants'", that are harmful to public health and the environment. These six criteria pollutants are:
- Ozone (O3)
- Atmospheric particulate matter (PM2.5/PM10)
- Lead (Pb)
- Carbon monoxide (CO)
- Sulfur oxides (SOx)
- Nitrogen oxides (NOx)
The Clean Air Act identifies two types of national ambient air quality standards: primary standards and secondary standards. While primary standards are designed to protect public health, secondary standards are designed to protect public welfare.
For example, in 1971, the secondary NAAQS for nitrogen dioxide (NO2) was set at an annual average of 0.053 ppm. The EPA reviewed this NAAQS in 1985 and 1996, concluding that the existing standard was sufficient. In 2010, the EPA reviewed the environmental impacts separately from the health impacts for the first time for this group of criteria air pollutants. As a result, a new 1-hour secondary standard of 100 ppb was established.
The NAAQS standards are periodically reviewed and revised. For instance, in 2015, the ozone standard was lowered to 70 ppb from 75 ppb, and the annual PM2.5 standard was lowered to 12 µg/m3 from 15 µg/m3 in 2012.
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Criteria Air Pollutants
The Clean Air Act requires the Environmental Protection Agency (EPA) to set National Ambient Air Quality Standards (NAAQS) for six principal pollutants, or "criteria pollutants", which are common in outdoor air and harmful to public health and the environment. These criteria air pollutants can be found all over the United States and can cause property damage, harm human health, and damage vegetation and crops.
The six criteria air pollutants are:
- Carbon Monoxide (CO): In the past, portions of states have been designated nonattainment for the 1971 CO standard.
- Nitrogen Oxides (NOx): NOx reacts with other chemicals in the air to form particulate matter, ozone, and acid rain. Nitrate particles that result from NOx reduce visibility and cause regional haze.
- Ozone (O3): Ozone is a gas composed of three atoms of oxygen. The 1979 1-hour and 1997 8-hour ozone standards have not been met in some areas.
- Sulfur Dioxide (SO2): SO2 largely comes from burning fossil fuels (coal and oil) in power plants and industrial facilities, as well as burning diesel fuel in vehicles. Short-term exposure can harm the human respiratory system.
- Particulate Matter (PM): Particulate matter is formed through the reaction of certain chemicals in the air, such as SO2 and NOx.
- Lead (Pb): In areas that have not met the Pb standards, previous standards remain in effect.
Primary NAAQS standards aim to protect public health, including sensitive populations such as asthmatics, children, and the elderly. Secondary NAAQS standards aim to protect public welfare, including crops, vegetation, animals, and buildings. The EPA periodically reviews the NAAQS for each of the six criteria pollutants to determine if changes are warranted based on scientific and technical information.
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Nitrogen Oxides
The Clean Air Act, last amended in 1990, requires the US Environmental Protection Agency (EPA) to set National Ambient Air Quality Standards (NAAQS) for six principal pollutants, referred to as "criteria pollutants." These pollutants are common in outdoor air and are considered harmful to public health and the environment. Nitrogen dioxide (NO2) is one of the six criteria pollutants for which the EPA has established NAAQS.
The NAAQS for NO2 aim to protect public health and welfare. Primary standards focus on safeguarding the health of sensitive populations, such as asthmatics, children, and the elderly. Secondary standards aim to protect against adverse effects on the environment, including damage to soils, water, crops, vegetation, animals, and buildings.
To meet the NAAQS for NO2, the EPA has implemented various measures, including monitoring and regulating emissions from vehicles and industrial sources. The EPA also works closely with state, tribal, and local air agencies to attain and maintain the required standards across the country.
The NAAQS for NO2 are periodically reviewed and revised as necessary to ensure they are up-to-date with the latest scientific and technical information. For example, in 2009, a proposed revision to the NO2 NAAQS was published, and in 2013, a final rule was issued, revising the ambient nitrogen dioxide monitoring requirements.
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Frequently asked questions
Ozone (O3), atmospheric particulate matter (PM2.5/PM10), lead (Pb), carbon monoxide (CO), sulfur oxides (SOx), and nitrogen oxides (NOx).
Criteria pollutants are those that are common in outdoor air and are harmful to public health and the environment. Anything that does not meet these criteria is not a criteria pollutant.
The two types of NAAQS standards are primary and secondary. The primary standards are designed to protect the health of 'sensitive' populations such as asthmatics, children, and the elderly. The secondary standards are concerned with protecting the environment and addressing visibility, damage to crops, vegetation, buildings, and animals.
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