Helena Joyce
Air pollution is a pressing global issue that poses significant health risks to people worldwide. It is a complex mixture of solid particles, liquid droplets, and gases, with sources ranging from household fuel burning to industrial emissions. While there are safety standards and guidelines in place, such as the National Ambient Air Quality Standards (NAAQS) in the US and the WHO Air Quality Guidelines globally, the negative health impacts of air pollution are well-documented and associated with millions of premature deaths annually. Fine particulate matter (PM2.5) and gases like nitrogen dioxide (NO2) have been linked to cardiovascular and respiratory issues, developmental delays, and psychological problems. The challenge lies in minimizing exposure to pollutants and recognizing that there is no safe amount of air pollution. Addressing air pollution requires concerted action from policymakers and society as a whole to reduce emissions and protect public health.
| Characteristics | Values |
|---|---|
| Air Quality Index (AQI) | AQI values at or below 100 are generally thought of as satisfactory. When AQI values are above 100, air quality is unhealthy: at first for certain sensitive groups of people, then for everyone as AQI values increase. |
| Clean Air Act | The Clean Air Act requires the EPA to set National Ambient Air Quality Standards (NAAQS) for six commonly found air pollutants known as "criteria" air pollutants. |
| Criteria Air Pollutants | Carbon monoxide (CO), ozone (O3), nitrogen dioxide (NO2), sulfur dioxide (SO2), sulfates, nitrates, ammonia, sodium chloride, black carbon, mineral dust, and water. |
| WHO Air Quality Guidelines | Interim targets to promote a gradual shift from high to lower concentrations and their associated health benefits. For example, through the achievement of interim target one (35 µg/m3), around 300,000 deaths would be saved worldwide annually. |
| No Safe Level of Air Pollution | There is strong empirical evidence that there is no "safe" amount of air pollution below which adverse effects do not occur. |
| Planning Considerations | Minimizing exposure to pollutants, not simply ensuring they are below arbitrary threshold standards. |
| Fine Particulate Matter | The effect was greatest on the day of high pollutant exposure and the succeeding 3 days, then began to decay. |
| NO2 | The effect was greatest in the 4 days after the exposure event. |
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What You'll Learn
There is no safe amount of air pollution
Air pollution is a major environmental health problem affecting individuals in low-, middle-, and high-income countries. It is the second-highest risk factor for non-communicable diseases, and there is no safe amount of air pollution. Even the smallest amount of exposure to minute soot particles, known as PM2.5, raises the risk of cardiovascular disease.
PM2.5 is a form of airborne pollution consisting of tiny particles of soot, measuring less than the width of a human hair. In the US, the annual allowable PM2.5 emissions have been cut from 12 micrograms per cubic meter to 9 micrograms per cubic meter. However, this is still above the World Health Organization (WHO) limit of 5 micrograms per cubic meter. According to a study published in the BMJ, the increased level of risk is significant, with the average pollution amount in the US causing a 29% jump in the risk of hospital admission.
The Clean Air Act requires the EPA to set National Ambient Air Quality Standards (NAAQS) for six commonly found air pollutants known as criteria air pollutants. These pollutants can harm human health and the environment and cause property damage. The six criteria air pollutants are particulate matter (PM), carbon monoxide (CO), ozone (O3), nitrogen dioxide (NO2), and two others. PM is a common proxy indicator for air pollution and has major components such as sulfates, nitrates, ammonia, sodium chloride, black carbon, mineral dust, and water. CO is a colorless, odorless, and toxic gas produced by the incomplete combustion of carbonaceous fuels such as wood, petrol, charcoal, natural gas, and kerosene. Ground-level O3 is a major constituent of photochemical smog and is formed through the reaction with gases in the presence of sunlight. NO2 is commonly released from the combustion of fuels in the transportation and industrial sectors.
The WHO Global Air Quality Guidelines (AQG) offer global guidance on thresholds and limits for key air pollutants that pose health risks. These guidelines are developed through a transparent, evidence-based decision-making process. The guidelines also provide interim targets to promote a gradual shift to lower concentrations and their associated health benefits. For example, achieving interim target one (35 µg/m3) would save around 300,000 deaths worldwide annually. In addition to quantitative guidance, the WHO also offers qualitative statements on the management of certain types of particulate matter, such as black carbon and ultrafine particles.
While the US, UK, and EU have air quality standards in place, these standards still allow for dangerous risks to public health. It is important for policymakers in sectors such as energy, transport, waste management, urban planning, and agriculture to take concerted action to reduce air pollution and protect public health.
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The Clean Air Act and National Ambient Air Quality Standards
The Clean Air Act (CAA) is a comprehensive federal law that regulates air emissions from stationary and mobile sources. It was last amended in 1990 to require the Environmental Protection Agency (EPA) to set National Ambient Air Quality Standards (NAAQS) for six principal pollutants ("criteria" air pollutants) that are harmful to public health and the environment. These criteria air pollutants are found all over the US. The six criteria air pollutants are:
- Lead (Pb)
- Nitrogen dioxide (NO2)
- Ground-level ozone (O3)
- Carbon monoxide (CO)
- Sulfur dioxide (SO2)
- Particle pollution, also known as particulate matter (PM)
The Clean Air Act identifies two types of NAAQS: primary standards and secondary standards. Primary standards aim to protect public health, including sensitive populations such as asthmatics, children, and the elderly. Secondary standards aim to protect public welfare, including crops, vegetation, and buildings. The NAAQS are set through a comprehensive process that involves scientific literature review, risk and exposure assessments, and public input. The EPA works with state, tribal, and local air agencies to achieve and maintain these standards.
The Menu of Control Measures (MCM) is a document that provides state, local, and tribal air agencies with information on existing emission reduction measures, efficiency, and cost-effectiveness. These agencies can then develop strategies, plans, and programs to meet the NAAQS. The MCM is a living document that can be updated with new data.
The Air Quality Index (AQI) is a scale used to communicate the level of pollution in the air. An AQI value of 100 corresponds to the level of the short-term NAAQS for protection of public health. Values above 100 indicate unhealthy air quality, first for sensitive groups and then for everyone as values increase.
California has its own ambient air quality standards (CAAQS), which predate the formation of the EPA and the adoption of the NAAQS. California's standards were established in 1959, and while they are still mandated by state law, the NAAQS take precedence.
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WHO Air Quality Guidelines and health impacts
The World Health Organization (WHO) air quality guidelines (AQGs) are a set of evidence-based recommendations of limit values for specific air pollutants. They are designed to help countries achieve air quality that protects public health. The guidelines are based on expert evaluations of current scientific evidence from multiple countries, making them relevant to diverse conditions worldwide. While they are not legally binding, governments can use them as a reference to develop standards that suit their unique, local conditions.
The first release of the guidelines was in 1987, with several updated versions appearing since then. The latest global version was published in 2005, and the guidelines are regularly updated to maintain their relevance and support a wide range of policy options for air quality management. The 2021 update, for example, focused on particulate matter, ozone, nitrogen dioxide, and sulfur dioxide.
WHO's Air Quality and Health Unit works in three key areas to reduce air pollution levels and protect populations from health risks: knowledge, evidence, and measuring progress; institutional capacity building and technical support; and leadership and coordination. The guidelines provide interim targets to promote a gradual shift towards lower pollutant concentrations, highlighting the associated health benefits. For instance, achieving interim target one (35 µg/m3) could save around 300,000 lives worldwide each year.
The guidelines also offer qualitative statements on managing certain types of particulate matter, such as black carbon/elemental carbon, ultrafine particles, and particles from sand and dust storms. This is because there is insufficient quantitative evidence to derive specific AQG levels for these pollutants. Fine particulate matter (PM2.5) can penetrate the lungs and enter the bloodstream, affecting all major organs. Exposure to PM2.5 is linked to cardiovascular and respiratory issues, including stroke, lung cancer, and chronic obstructive pulmonary disease (COPD).
In 2019, 99% of the world's population lived in areas that did not meet WHO air quality guidelines. Ambient outdoor air pollution is estimated to have caused 4.2 million premature deaths worldwide in 2019, with 89% of these occurring in low- and middle-income countries. Air pollution is the largest environmental health risk in Europe, causing cardiovascular and respiratory issues that lead to the loss of healthy years of life and premature deaths.
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Pollutants and their sources
Air pollution is the release of various gases, finely divided solids, or finely dispersed liquid aerosols into the atmosphere at rates that exceed the environment's capacity to dilute or absorb them. These pollutants can have harmful effects on human health and the environment.
There are four main types of air pollution sources: mobile, stationary, area, and natural. Mobile sources, which account for more than half of the air pollution in the United States, include cars, buses, trucks, and trains. The primary mobile source of air pollution is the automobile. Stationary sources, such as power plants, oil refineries, industrial facilities, and factories, emit large amounts of pollution from a single location and are also known as point sources. Area sources, such as agricultural areas, cities, and wood-burning fireplaces, are made up of smaller pollution sources that can collectively have a significant impact. Natural sources, such as wind-blown dust, wildfires, and volcanoes, can also contribute to air pollution, but they typically do not create ongoing pollution problems.
Some of the main gaseous criteria air pollutants of concern, especially in urban areas, include sulfur dioxide, nitrogen dioxide, and carbon monoxide. These pollutants are emitted directly into the air from the burning of fossil fuels such as fuel oil, gasoline, and natural gas in power plants, automobiles, and other combustion sources. Another gaseous pollutant, ozone, is a key component of smog and forms in the atmosphere through complex chemical reactions between nitrogen dioxide and volatile organic compounds like gasoline vapors.
Particulate matter, or airborne suspensions of extremely small solid or liquid particles, is also a significant pollutant. Examples include soot, dust, smokes, fumes, and mists, especially those less than 10 micrometres in size, as they can have harmful effects on human health. Lead fumes, with particulate sizes of less than 0.5 micrometres, are particularly toxic and are commonly found in diesel fuels.
The Clean Air Act, last amended in 1990, requires the EPA to set National Ambient Air Quality Standards (NAAQS) for six principal pollutants ("criteria" air pollutants) that can harm public health and the environment. These criteria air pollutants are found throughout the United States and include the pollutants mentioned above. The EPA establishes an Air Quality Index (AQI) for each of these pollutants, with an AQI value of 100 corresponding to the short-term national ambient air quality standard for protection of public health. Values above 100 indicate unhealthy air quality for certain sensitive groups and then for everyone as values increase.
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Strategies to reduce pollution
The Clean Air Act requires the Environmental Protection Agency (EPA) to set National Ambient Air Quality Standards (NAAQS) for six major air pollutants that can be harmful to public health and the environment. These pollutants are commonly found across the United States and are known as "criteria" air pollutants. The EPA also establishes an Air Quality Index (AQI) for these pollutants, with an AQI value of 100 corresponding to the short-term NAAQS for protection of public health.
To reduce air pollution, individuals can take several measures, including:
- Choosing cleaner commutes, such as carpooling, using public transportation, biking, or walking.
- Conserving energy by using energy-efficient appliances and heating systems, turning off electrical items when not in use, and setting air conditioners no lower than 78 degrees.
- Reducing the use of cars, especially those with diesel engines, and considering switching to electric or hybrid vehicles.
- Limiting the burning of garbage and firewood, as this can release harmful pollutants into the air and negatively impact health and the environment.
- Encouraging the use of electric or hand-powered lawn equipment instead of gas-powered engines, which often lack pollution control devices.
- Promoting walking and cycling to reduce congestion and lower CO2 emissions from cars, which contribute significantly to overall UK emissions.
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Frequently asked questions
There is no safe amount of air pollution. While there are standards and guidelines in place, such as the National Ambient Air Quality Standards (NAAQS) in the US and the WHO Air Quality Guidelines, these are not safe thresholds below which there are no adverse health effects. Instead, they are targets to work towards to reduce the health impacts of air pollution and protect public health.
The Clean Air Act requires the EPA to set NAAQS for six commonly found air pollutants, also known as criteria air pollutants. These pollutants are harmful to public health and the environment. NAAQS includes primary standards, which protect public health, and secondary standards, which protect against damage to the environment.
The WHO Air Quality Guidelines are a set of recommendations for limit values of specific air pollutants. They are based on scientific evidence and aim to help countries achieve air quality that protects public health. While they are not legally binding, governments can use them as guidance to reduce air pollution and its health impacts.
