Air Pollutants: What's Not A Criteria Pollutant?

The Clean Air Act requires the US Environmental Protection Agency (EPA) to set National Ambient Air Quality Standards (NAAQS) for six commonly found air pollutants known as criteria air pollutants. These pollutants are harmful to public health and the environment and can cause property damage. The six criteria air pollutants are: carbon monoxide, nitrogen oxide, tropospheric ozone, sulfur dioxide, particulate matter, and lead. These pollutants are found all over the US and are regulated by the EPA to protect the health of sensitive populations and the environment. The EPA works with state, tribal, and local air agencies to attain and maintain air quality standards through various measures, such as implementing emission reduction strategies.

The Clean Air Act

Amendments to the Clean Air Act were made in 1977 to address areas that had not met the NAAQS requirements. These amendments introduced more stringent measures for emission reduction in non-compliant areas and established the Prevention of Significant Deterioration (PSD) regulations for regions already meeting the standards. The PSD regulations aimed to prevent any notable worsening of air quality, maintaining it above a predetermined baseline level.

Section 112 of the Clean Air Act specifically addresses hazardous air pollutant emissions. The 1990 amendments to this section mandated the issuance of technology-based standards for "major sources" and certain "area sources." Major sources refer to stationary sources or groups of stationary sources with the potential to emit 10 tons or more of a hazardous air pollutant annually, or a combination of such pollutants totaling 25 tons or more per year. The EPA is required to establish emission standards, known as Maximum Achievable Control Technology (MACT) standards, for these major sources to ensure the maximum feasible reduction in hazardous air pollutant emissions.

National Ambient Air Quality Standards

The United States National Ambient Air Quality Standards (NAAQS) are limits on the atmospheric concentration of six pollutants that cause smog, acid rain, and other health hazards. These six criteria air pollutants (CAP), or criteria pollutants, are: ozone (O3), atmospheric particulate matter (PM2.5/PM10), lead (Pb), carbon monoxide (CO), sulfur oxides (SOx), and nitrogen oxides (NOx).

The Clean Air Act requires the Environmental Protection Agency (EPA) to set these standards for the six principal pollutants, which are common in outdoor air and harmful to public health and the environment. The Act identifies two types of national ambient air quality standards: 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, including visibility, damage to crops, vegetation, buildings, and animals.

The EPA established the NAAQS according to Sections 108 and 109 of the US Clean Air Act, which was last amended in 1990. The standards are reviewed and sometimes revised to establish new standards. The most recent review took place in 1996, where the EPA considered implementing a new NAAQS for 5-minute peaks of SO2 affecting sensitive populations, but ultimately decided to maintain the existing standards. In 2010, the EPA replaced the dual primary standards with a new 1-hour standard set at 75 ppb.

Units of measure for the standards are parts per million (ppm) by volume, parts per billion (ppb) by volume, and micrograms per cubic meter of air (µg/m3). For example, the level of the annual NO2 standard is 0.053 ppm. The EPA also set the first NAAQS for carbon monoxide in 1971, with the primary standard set at 9 ppm averaged over an 8-hour period and 35 ppm over a 1-hour period.

Harmful to public health and the environment

Air pollution is a major cause for concern when it comes to public health and the environment. It is the single largest environmental health risk in Europe, and it affects people all over the world. According to the World Health Organization (WHO), air pollution is responsible for nearly seven million deaths globally each year. The effects of air pollution can be detrimental to human health, causing a wide range of diseases and health complications. It can also have economic impacts, such as increased medical costs and missed workdays.

Fine particulate matter (PM2.5) is one of the most harmful air pollutants. These tiny particles can penetrate deep into the lungs and enter the bloodstream, causing systemic damage to tissues and cells. They can also worsen existing health conditions, such as asthma and bronchitis, and increase the risk of heart attacks. In addition, exposure to PM2.5 has been linked to an increased risk of cancer, with the International Agency for Research on Cancer classifying it as a leading cause.

Other harmful air pollutants include ozone (O3), nitrogen dioxide (NO2), carbon monoxide (CO), and sulphur dioxide (SO2). These pollutants can cause respiratory issues, inflammation, oxidative stress, immunosuppression, and mutagenicity in cells. They can also have adverse effects on children, with evidence suggesting that exposure to air pollution during childhood can increase the risk of diseases later in life. Older individuals and those with pre-existing health conditions are also more susceptible to the harmful effects of air pollution.

The sources of air pollution are varied, but most air pollution comes from energy use and production, such as burning fossil fuels for transportation, heating, and power generation. The release of harmful chemicals and gases from these processes contributes to the degradation of air quality. To address this issue, organizations like the WHO and the European Commission have developed guidelines and commitments to improve air quality and reduce pollution levels to protect public health and the environment.

In summary, air pollution poses a significant threat to public health and the environment. It increases the risk of various diseases, exacerbates existing health conditions, and can even lead to premature death. Fine particulate matter is of particular concern, along with other common air pollutants. The sources of air pollution are diverse, but efforts are being made to mitigate their impacts and improve air quality through regulations, standards, and targeted measures. These actions are crucial to safeguard the well-being of people and the planet.

Primary and secondary standards

The Clean Air Act requires the Environmental Protection Agency (EPA) to set National Ambient Air Quality Standards (NAAQS) for six criteria pollutants: fine particle pollution, ozone, carbon monoxide, lead, nitrogen dioxide, and sulfur dioxide. These pollutants are common in outdoor air and can be harmful to public health and the environment.

The NAAQS are comprised of two types of standards: primary and secondary. Primary standards are those that protect public health, specifically the health of "sensitive" populations such as asthmatics, children, and the elderly. These standards aim to safeguard vulnerable individuals from the detrimental effects of air pollution.

On the other hand, secondary standards focus on public welfare protection. These standards address issues like decreased visibility and damage to animals, crops, vegetation, and buildings. They seek to minimise the indirect impacts of air pollution on communities and the environment.

The NAAQS are periodically reviewed and revised to ensure their effectiveness and relevance. For instance, in 2015, the ozone standard was lowered from 75 ppb to 70 ppb, and this remained unchanged during the 2020 review. Similarly, in 2012, the annual PM2.5 standard was lowered to 12 µg/m3 from 15 µg/m3 and has been maintained at that level.

State, local, and tribal agencies utilise the NAAQS to develop emission reduction strategies, plans, and programs. This ensures compliance with the standards and helps protect public health and the environment from the harmful effects of air pollution. The Menu of Control Measures (MCM) is a valuable resource for these agencies, providing information on existing emission reduction measures and their efficiency and cost-effectiveness.

Units of measure for the standards

The Clean Air Act requires the US Environmental Protection Agency (EPA) to set National Ambient Air Quality Standards (NAAQS) for six principal pollutants, or "criteria" air pollutants, which are harmful to public health and the environment. The six criteria air pollutants are particulate matter, ozone, carbon monoxide, sulfur dioxide, nitrogen dioxide, and lead.

The EPA establishes NAAQS based on the latest scientific information regarding the effects of these pollutants on health and welfare. The NAAQS are set in terms of specific units of measure to determine the acceptable or unacceptable concentrations of pollutants in the air. The units of measure for the standards are typically expressed in parts per million (ppm).

For example, the previous standards for sulfur dioxide (SO2) were set at 0.14 ppm for a 24-hour period and 0.03 ppm as an annual average. These standards remain in effect in certain areas, such as areas that have not yet reached one year since the effective date of designation under the current (2010) standards.

The EPA also considers other factors, such as the visibility-reducing effects of pollutants like NOx, which reacts with other chemicals to form particulate matter, ozone, and acid rain. The EPA's standards aim to protect public health, especially sensitive populations like asthmatics, children, and the elderly, and to safeguard the environment, including crops, vegetation, and buildings.

To ensure compliance with the NAAQS, the EPA designates areas as meeting (attainment) or not meeting (nonattainment) the standards. States are required to develop and submit specific implementation plans (SIPs) to achieve and maintain the standards, particularly for areas designated as nonattainment. These plans address emission reduction measures and their effectiveness, aiming to improve air quality across the country.

Frequently asked questions