Epa's Air Quality Monitoring: Six Key Pollutants

The United States Environmental Protection Agency (EPA) is mandated by the Clean Air Act to set National Ambient Air Quality Standards (NAAQS) for six principal pollutants, known as criteria pollutants, that are prevalent in outdoor air and pose risks to human health and the environment. These six criteria air pollutants, which include carbon monoxide, lead, ground-level ozone, particulate matter, nitrogen dioxide, and sulfur dioxide, are monitored by the EPA through ambient air monitors placed across the country, with a focus on areas expected to have higher pollutant concentrations or larger populations. The EPA works in collaboration with state, local, and tribal agencies to implement emission reduction strategies and ensure compliance with the NAAQS, striving to improve air quality and safeguard public health and welfare.

Carbon monoxide

CO is a significant air pollutant that contributes to climate change and adversely affects human health. It participates in chemical reactions in the atmosphere that produce ozone, a known climate change gas. Additionally, when inhaled, CO reduces the amount of oxygen delivered to the body's organs and tissues, potentially leading to serious health issues, especially for individuals with heart disease.

Outdoor air pollution by CO is primarily attributed to vehicles and machinery that burn fossil fuels. Higher levels of CO are typically found in areas with heavy traffic congestion. Industrial processes, such as metal processing and chemical manufacturing, as well as residential wood burning and natural sources like forest fires, also contribute to outdoor CO emissions.

Indoor CO levels can be significantly higher than outdoors. In addition to the indoor sources mentioned earlier, indoor air quality can be affected by outdoor sources, especially in enclosed environments. Elevated CO levels can be of particular concern for individuals with heart disease, as it may cause chest pain, reduced exercise capacity, and other cardiovascular effects. Even healthy individuals can experience negative effects from high CO exposure, including vision problems, reduced cognitive function, and difficulty performing complex tasks.

Lead

The six most common air pollutants are called "criteria" air pollutants and include carbon monoxide (CO), lead (Pb), ground-level ozone (O3), particulate matter (PM), nitrogen dioxide (NO2), and sulfur dioxide (SO2). These pollutants are monitored by the EPA through its Air Quality System (AQS) database, which collects data from ambient air monitors placed throughout the United States.

The sources of lead pollution vary, but some common sources include industrial emissions, vehicle exhaust, and lead-based paint. Lead can be released into the air during the manufacturing, burning, or disposal of products containing lead. Older houses may also contain lead-based paint, which can deteriorate over time and release lead dust and chips into the air.

The EPA has set National Ambient Air Quality Standards (NAAQS) for lead to protect public health and welfare. These standards aim to limit the amount of lead in the air to safe levels. The EPA works with state, tribal, and local air agencies to enforce these standards and reduce lead emissions.

To monitor lead pollution, the EPA deploys ambient air monitors in areas with expected higher lead concentrations or larger populations. While not every county in the United States has air pollution monitors, the monitors are strategically placed to capture long-term trends and support data analysis. The data collected from these monitors helps the EPA assess compliance with the NAAQS for lead and drive actions to improve air quality.

In 2021, it was reported that 0.1% of U.S. children lived in a county with lead concentrations above the level of the three-month standard. This highlights the ongoing importance of monitoring and regulating lead pollution to safeguard public health, especially that of vulnerable populations.

Ground-level ozone

Tropospheric or ground-level ozone is not emitted directly into the air but is created by chemical reactions between oxides of nitrogen and volatile organic compounds. This occurs when pollutants emitted by cars, power plants, industrial boilers, refineries, chemical plants, and other sources chemically react in the presence of sunlight. Ground-level ozone levels are typically higher on hot sunny days in urban environments, but they can still reach high levels during the colder months. The transport of ozone over long distances by wind can result in high ozone levels even in rural areas.

Particulate matter

The EPA uses the term PM to refer to particulate matter. PM10 refers to inhalable coarse particles with diameters between 2.5 and 10 micrometers, while PM2.5 refers to fine particles with diameters of 2.5 micrometers or less. These fine particles pose the greatest risk to health, as they can get deep into the lungs and even into the bloodstream. They are also the main cause of reduced visibility (haze) in some areas of the United States.

The health effects of inhaling particulate matter have been widely studied, and exposure to PM has been linked to a range of adverse health outcomes. These include respiratory illnesses such as asthma, lung cancer, cardiovascular disease, developmental disorders, neurodegenerative disorders, mental disorders, and even premature death. Fine particulate matter has been found to be particularly harmful, with studies showing that it is responsible for the majority of deaths and hospital visits caused by particulate matter in the air.

The EPA regulates inhalable particles and has implemented rules to reduce emissions of pollutants that form particulate matter, helping state and local governments meet the Agency's national air quality standards. The Air Quality Index (AQI) is a useful tool that informs individuals about the quality of their outdoor air and any associated health risks, allowing them to take necessary protective actions.

Nitrogen dioxide

NO2 primarily gets in the air from the burning of fuel. Emissions from cars, trucks, and buses, power plants, and off-road equipment are the main sources of NO2. Trucks, buses, and cars are the largest sources of NO2 emissions, followed by diesel-powered non-road equipment, industrial processes such as oil and gas production, industrial boilers, and other movable engines, and coal-fired power plants. Monitors show the highest concentrations of outdoor NO2 in large urban regions such as the Northeast corridor, Chicago, and Los Angeles. Levels are higher on or near heavily traveled roadways.

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