National Ambient Air Quality Standards
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What are the National Ambient Air Quality Standards (NAAQS)?
The National Ambient Air Quality Standards (NAAQS) are air pollutant levels set by the Environmental Protection Agency (EPA) according to the Clean Air Act (CAA).
The CAA established primary and secondary standards for ambient air quality. Primary standards protect public health, especially for sensitive groups like children, the elderly, and people with asthma. Secondary standards aim to protect public welfare, prevent damage to animals, plants, and property.
NAAQS has set standards for six main pollutants, known as criteria pollutants: carbon monoxide, lead, nitrogen dioxide, particulate matter, sulfur dioxide, and ground-level ozone. From 1970 to 2022, emissions of these major air pollutants dropped 78% in the United States.
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Why were the National Ambient Air Quality Standards created?
The National Ambient Air Quality Standards (NAAQS) were created by the Environmental Protection Agency (EPA) following the Clean Air Act (CAA) of 1970 to combat air pollution, protect the ozone layer, and promote public health.
NAAQS set allowable levels for six main pollutants, known as criteria pollutants, that can be harmful: carbon monoxide, lead, nitrogen dioxide, particulate matter, sulfur dioxide, and ground-level ozone. The primary standards ensure air quality protects public health, especially for sensitive groups such as children, the elderly, and people with asthma. The secondary standards aim to protect public welfare by preventing damage to animals, plants, and property. States must meet these standards or face penalties.
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Which main air pollutants are covered by the NAAQS?
The National Ambient Air Quality Standards (NAAQS) covers six main air pollutants, also known as criteria pollutants. These are carbon monoxide, lead, nitrogen dioxide, particulate matter (airborne suspensions of extremely small solid or liquid particles), sulfur dioxide, and ground-level ozone. The Environmental Protection Agency (EPA) set these allowable levels of harmful air pollutants in accordance with the Clean Air Act (CAA).
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Who is responsible for setting and enforcing the NAAQS?
The Environmental Protection Agency (EPA) is responsible for setting and enforcing the National Ambient Air Quality Standards (NAAQS) in accordance with the Clean Air Act (CAA). These standards include primary standards to protect public health and secondary standards to prevent damage to animals, plants, and property. States must create plans to meet these standards, but they cannot have weaker pollution controls than the NAAQS.
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How do these standards affect what factories and cars can release into the air?
The National Ambient Air Quality Standards (NAAQS) set by the EPA under the Clean Air Act (CAA) impact the permissible levels of specific pollutants that factories and cars can release. These standards define the maximum acceptable concentrations of six major air pollutants, known as criteria pollutants: carbon monoxide, lead, nitrogen dioxide, particulate matter, sulfur dioxide, and ground-level ozone.
The CAA authorizes the EPA to establish New Source Performance Standards (NSPS), regulating emissions from various facilities, considering air quality, environmental impact, energy requirements and cost for businesses. States must meet these standards or face penalties. Individual states can have stronger pollution controls, but none can have weaker pollution controls than those set for the country as a whole.
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What happens if an area does not meet the NAAQS requirements?
If an area does not meet the National Ambient Air Quality Standards (NAAQS), it faces substantial "nonattainment" fines and penalties. The Clean Air Act (CAA) requires all states, cities, and towns in the United States to maintain levels of six major pollutants—sulfur dioxide, nitrogen dioxide, particulate matter, carbon monoxide, ground-level ozone, and lead—beneath the ceilings mandated by the NAAQS. States are responsible for creating plans, known as state implementation plans, to meet these standards for air quality regions within their borders.
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National Ambient Air Quality Standards (NAAQS), in the United States, allowable levels of harmful air pollutants set by the Environmental Protection Agency (EPA) in accordance with the Clean Air Act (CAA). The CAA established two types of standards for ambient air quality. Primary standards concern the minimum level of air quality necessary to keep people from becoming ill and therefore are aimed at protecting public health. The primary standards are intended to provide an adequate margin of safety for the public, which has been defined to include a representative sample of so-called sensitive populations, such as children, older people, and persons with asthma. The secondary standards are aimed at the promotion of public welfare and the prevention of damage to animals, plants, and property.
(Read Britannica’s essay “What Happened to Acid Rain?”)
National Ambient Air Quality Standards (NAAQS) have been set for six principal pollutants known as criteria pollutants. These are carbon monoxide, lead, nitrogen dioxide, particulate matter (airborne suspensions of extremely small solid or liquid particles), sulfur dioxide, and ground-level ozone (ozone is not directly emitted into the air but is formed by sunlight acting on emissions of nitrogen oxides and volatile organic compounds). There are two categories of particulate matter: coarse inhalable particles with dimensions between 2.5 and 10 micrometers (μm) and fine inhalable particles that are 2.5 μm or less (1 μm = 10−6 meter). Each of the categories has different primary standards. NAAQS for criteria pollutants are performance rather than design standards: they set the performance levels to be achieved as opposed to specifying the equipment that needs to be installed to clean up air pollution.
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Six major air pollutants have been designated by the U.S. Environmental Protection Agency as “criteria” pollutants—meaning that the concentrations of these pollutants in the atmosphere are useful as indicators of overall air quality.
- ground-level ozone
See also The six criteria air pollutants.
Because air pollution problems vary from place to place throughout the United States, a regional concept was adopted for air pollution control through the establishment of air quality control regions. An air quality control region is defined by the EPA as an area with established pollution problems, common pollution sources, and characteristic weather. States were given the responsibility of drawing up plans (state implementation plans) to attain the standards for the air quality regions within their boundaries. Individual states may have stronger pollution controls than listed by NAAQS. However, none can have weaker pollution controls than those set for the country as a whole.
Local ambient air quality is reported online using the air quality index (AQI), which communicates whether the relative air quality and air pollution level in a given area is healthy or unhealthy. Maps of local AQI values use color-coded air hazard levels (green, yellow, orange, red, purple, or maroon) to convey outdoor air pollution; the closer to maroon, the worse the air quality conditions. The AQI focuses on roughly 24-hour periods, allowing individuals to take precautionary measures to avoid acute health effects.