Meghan Hodges
The Clean Air Act, enacted in 1970, established regulations to control six common pollutants that formed dense, visible smog in many cities and industrial centers across the United States. These six criteria pollutants, including particulate matter, ozone, carbon monoxide, sulfur dioxide, nitrogen dioxide, and lead, are known for their detrimental effects on human health and the environment. While significant progress has been made in reducing emissions, it is important to continuously monitor and address these pollutants to ensure the well-being of our planet and its inhabitants.
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What You'll Learn
Particulate matter
PM is commonly referred to as particle pollution and is found everywhere, not just in haze, smoke, and dust, but also in air that appears to be clean. It is produced by a variety of sources, including construction sites, unpaved roads, fields, smokestacks, and fires. Some particles are emitted directly from these sources, while others form in the atmosphere as a result of complex reactions between chemicals such as sulfur dioxide and nitrogen oxides.
Particle pollution can remain in the atmosphere for days to weeks and can travel long distances, affecting the air quality of regions far from the original source. Levels of particle pollution are often higher near busy roads, in urban areas (especially during rush hour), and in industrial areas.
Of particular concern are the fine particles, known as PM2.5, which have diameters of 2.5 micrometers or less. These particles can be inhaled and pose serious health risks, including adverse effects on the respiratory system. Short-term exposures to larger particles (PM10) have been linked to worsening respiratory diseases, while long-term exposure to PM2.5 has been associated with premature death, especially in individuals with chronic heart or lung diseases.
To address the issue of particulate matter pollution, the EPA has implemented rules to reduce emissions of pollutants that form PM, helping state and local governments meet national air quality standards.
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Ozone
Tropospheric or ground-level ozone is the main ingredient in "smog." 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. People at the greatest risk of harm from breathing air containing ozone include those with asthma. Ozone is most likely to reach unhealthy levels on hot sunny days in urban environments, but it can still reach high levels during colder months.
To improve air quality, states must draft a state implementation plan (SIP) to improve air quality in nonattainment areas. The EPA's national and regional rules to reduce emissions of pollutants that form ground-level ozone help state and local governments meet the Agency's national air quality standards. Actions include vehicle and transportation standards, regional haze and visibility rules, and regular reviews of the NAAQS.
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Carbon monoxide
The main sources of carbon monoxide emissions are vehicles, gas-powered furnaces, and portable generators. In homes, carbon monoxide can come from gas stoves, leaking furnaces, car exhaust from attached garages, and space heaters.
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Sulfur dioxide
The major sources of sulfur dioxide emissions include the burning of fossil fuels, particularly coal, in utility and industrial boilers, as well as automobiles and trucks. In the United States, New Hampshire experienced violations of SO2 NAAQS in the late 1970s, but the state has been in attainment for SO2 since the early 1980s.
To address sulfur dioxide pollution, the EPA is responsible for establishing and updating NAAQS for SO2. Additionally, states may develop State Implementation Plans (SIPs) to outline the steps necessary to achieve and maintain the NAAQS. These plans include measures such as emission controls on power plants and vehicles to reduce SO2 emissions and improve air quality.
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Nitrogen dioxide
Sources of NO2 include the burning of fuels in utility and industrial boilers, as well as automobiles and trucks. While emission controls have been implemented in power plants and vehicles, the increasing energy demand and vehicle mileage have reduced the effectiveness of these measures.
The health impacts of NO2 include irritation of the airways, aggravation of asthma, and increased susceptibility to respiratory infections. The nitrate particles formed from NOx reduce visibility and contribute to regional haze, which blocks natural sunlight. Additionally, NOx in the atmosphere leads to nutrient pollution in coastal waters.
To address the harmful effects of NO2 and other criteria air pollutants, the Clean Air Act requires the EPA to establish National Ambient Air Quality Standards (NAAQS). These standards aim to protect public health and welfare by setting criteria for common air pollutants, including particulate matter, ozone, carbon monoxide, sulfur dioxide, and lead.
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Frequently asked questions
Criteria pollutants are common in New Hampshire, the United States, and much of the world. They are generally combustion products released by the burning of fossil fuels.
The six criteria pollutants are particulate matter, ozone, carbon monoxide, sulfur dioxide, nitrogen dioxide, and lead.
Carbon dioxide is not one of the six criteria pollutants.
Sources of the six criteria pollutants include fossil fuel combustion, industrial boilers, automobiles, trucks, and buses.
The health effects of the six criteria pollutants include respiratory problems, heart attacks, strokes, asthma attacks, and even premature death.
