Bronte Wells
The Clean Air Act, enacted in 1970, requires the EPA to establish National Ambient Air Quality Standards (NAAQS) for six common air pollutants, also known as criteria air pollutants. These pollutants are widespread and harmful to human health, the environment, and property. They are formed by the combustion of fossil fuels and include particulate matter, ozone, carbon monoxide, sulfur dioxide, nitrogen dioxide, and lead. These criteria pollutants are monitored by the EPA through ambient air monitors placed across the United States, particularly in areas with expected higher pollutant concentrations or larger populations.
| Characteristics | Values |
|---|---|
| Number of pollutants | 6 |
| Pollutants | Carbon monoxide (CO), lead (Pb), ground-level ozone (O3), particulate matter (PM), nitrogen dioxide (NO2), and sulfur dioxide (SO2) |
| Health effects | Coughing, wheezing, aggravation of respiratory illnesses such as asthma, neurodevelopmental effects (for lead), premature death in people with heart or lung disease, nonfatal heart attacks, irregular heartbeat, decreased lung function, etc. |
| Data source | EPA’s Air Quality System (AQS) database |
| Air Quality Index (AQI) categories | Good, moderate, unhealthy, hazardous, and no monitoring data |
| Air Quality Index (AQI) values | Unhealthy category: AQI values above 100 |
| Trends in air quality | Percentage of children’s days with “good” air quality increased from 38% in 1999 to 53% in 2021. Percentage of children’s days designated as having “unhealthy” air quality decreased from 10% in 1999 to 4% in 2021. |
| Population affected | In 2021, almost 75% of Asian non-Hispanic children lived in counties where air quality standards for any pollutant were exceeded. This was followed by Hispanic children (73%), Black non-Hispanic (59%), White non-Hispanic (51%), and other racial groups. |
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What You'll Learn
Particulate matter
PM is classified into two main categories based on particle size: PM10 and PM2.5. PM10 refers to inhalable particles with diameters generally 10 micrometres and smaller. PM2.5, on the other hand, denotes fine inhalable particles with diameters of 2.5 micrometres or less. These fine particles pose the greatest risk to health as they can penetrate deep into the lungs and even enter the bloodstream. Exposure to PM10 and PM2.5 has been linked to adverse health effects, particularly for individuals with heart or lung disease. Short-term exposure to PM10 can worsen respiratory conditions such as asthma and COPD, while long-term exposure to PM2.5 has been associated with premature death and reduced lung function growth in children.
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Ozone
However, at ground level, ozone is a harmful air pollutant and is the primary constituent of smog. Ground-level ozone is formed by chemical reactions between nitrogen oxides (NOx) and volatile organic compounds (VOCs). Cars, power plants, industrial boilers, refineries, chemical plants, and other sources emit pollutants that react chemically in the presence of sunlight to form ground-level ozone. On hot, sunny days in urban areas, ozone levels are more likely to be unhealthy. Nonetheless, high ozone levels can also occur during the colder months, and wind can carry ozone over long distances, causing even rural areas to experience high ozone levels.
The Clean Air Act mandates that the EPA establish National Ambient Air Quality Standards (NAAQS) for six common air pollutants, including ozone, to protect public health and welfare. These pollutants are referred to as "criteria" air pollutants because the EPA sets NAAQS for them based on specific criteria, such as the latest scientific information on their health and welfare effects. States must develop implementation plans to improve air quality in areas that do not meet the standards, and the EPA works with state, tribal, and local air agencies to achieve and maintain compliance with the NAAQS.
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Carbon monoxide
The primary sources of carbon monoxide emissions are vehicle exhausts, gas-powered furnaces, and portable generators. In homes, gas stoves, leaking furnaces, car exhaust from attached garages, and space heaters can contribute to carbon monoxide levels. Additionally, areas with high traffic congestion, such as parking garages, tunnels, or traffic signals surrounded by buildings, tend to have higher concentrations of carbon monoxide due to vehicle emissions.
The health risks associated with carbon monoxide exposure are particularly concerning for individuals with certain types of heart disease. These individuals may experience chest pains during physical activity or periods of higher stress. Even at low concentrations, carbon monoxide can cause fatigue, while higher concentrations may lead to impaired vision and nausea. Therefore, it is crucial to maintain proper ventilation and take preventive measures to minimize carbon monoxide exposure, especially in indoor environments.
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Sulfur dioxide
The presence of sulfur dioxide in the air can have significant health consequences. When inhaled, it can irritate the respiratory system, causing coughing, throat irritation, and airway inflammation. It can also worsen existing respiratory conditions such as bronchitis, emphysema, and asthma. People with these conditions, as well as children, older adults, and those who are active outdoors, are particularly vulnerable to the harmful effects of sulfur dioxide pollution.
Elevated concentrations of SO2 can also have detrimental effects on the natural environment. Gaseous sulfur oxides, including SO2, can contribute to acid rain, which damages foliage and decreases the growth of trees and plants. This, in turn, can disrupt ecosystems and negatively impact biodiversity. Additionally, the formation of particulate matter from SO2 can have indirect effects on the environment, such as reducing visibility and contributing to climate change.
To address the harmful effects of sulfur dioxide and other criteria pollutants, the EPA works with state, tribal, and local agencies to implement and enforce air quality standards. These standards aim to reduce emissions, improve air quality, and protect public health and the environment. As a result of these efforts, significant reductions in criteria pollutant emissions have been achieved over the years, leading to improved air quality and positive health outcomes for millions of people in the United States.
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Nitrogen dioxide
Sources of nitrogen dioxide include vehicle emissions, power plants, and off-road equipment that burns fuel at high temperatures. Additionally, road traffic is the primary outdoor contributor to nitrogen dioxide pollution. Indoor sources, such as tobacco smoke and the burning of fuels like gas, wood, oil, kerosene, and coal in appliances, can also significantly increase nitrogen dioxide levels.
The health risks associated with nitrogen dioxide exposure are particularly pronounced for individuals with asthma, young children, and the elderly. Studies have shown that nitrogen dioxide exposure can cause cell injury and inflammation, membrane damage, and increased membrane permeability in human cells. Furthermore, nitrogen dioxide can irritate the lungs and compromise immune responses to respiratory infections.
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Frequently asked questions
The Clean Air Act requires the Environmental Protection Agency (EPA) to set National Ambient Air Quality Standards (NAAQS) for six common air pollutants, known as criteria air pollutants. These pollutants are common in the United States and much of the world and can harm human health, the environment, and cause property damage.
The six criteria air pollutants are: particulate matter (or particle pollution), ground-level ozone, carbon monoxide, sulfur dioxide, nitrogen dioxide, and lead.
Exposure to criteria air pollutants has been associated with adverse health effects such as coughing, wheezing, and aggravation of respiratory illnesses like asthma. Children may be especially vulnerable to these pollutants as their organ systems are still developing, and they may experience higher exposure due to their outdoor activities.
