Brian Barton
Air pollution is a pressing global issue that poses significant health risks to people worldwide. In 2019, 4.2 million premature deaths were attributed to ambient (outdoor) air pollution, with 89% of these occurring in low- and middle-income countries. The World Health Organization (WHO) has developed global air quality guidelines (AQG) to address this problem by providing thresholds and limits for key air pollutants. These guidelines, most recently updated in 2021, aim to reduce the health effects of air pollution, including cardiovascular and respiratory diseases, and cancers. While they are not legally binding, the WHO guidelines offer valuable targets for countries to work towards improving air quality and protecting the health of their citizens.
| Characteristics | Values |
|---|---|
| Particulate matter (PM) | PM2.5 should not exceed 5 μg/m3 annual mean, or 15 μg/m3 24-hour mean; PM10 should not exceed 15 μg/m3 annual mean, or 45 μg/m3 24-hour mean |
| Ozone (O3) | No higher than 100 μg/m3 for an 8-hour mean and 60 μg/m3 peak season mean |
| Nitrogen dioxide (NO2) | 10 μg/m3 for the annual mean or 25 μg/m3 for a 24-hour mean |
| Sulfur dioxide (SO2) | Concentrations not exceeding 40 μg/m3 24-hour mean |
| Carbon monoxide (CO) | Not specified |
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What You'll Learn
Interim targets for gradual reduction of pollutant concentrations
The World Health Organization's (WHO) Global Air Quality Guidelines (AQG) provide interim targets to promote a gradual shift from high to lower concentrations of pollutants and their associated health benefits. These targets are unique to the 2021 guidelines and are designed to be achievable in a graded manner.
The targets are designed to reduce the health impacts of air pollution, although they are neither standards nor legally binding criteria. The guidelines offer qualitative statements on good practices for the management of certain types of particulate matter (PM), for which there is insufficient quantitative evidence to derive AQG levels. This includes practices for the management of black carbon/elemental carbon, ultrafine particles, and particles originating from sand and dust storms.
The achievement of interim target one (35 µg/m3) would save an estimated 300,000 deaths worldwide annually. This target is designed to be realistic and achievable, with gradual improvements in air quality at each location. For example, in India, higher levels of air pollutants, including PM2.5, have been recorded, and the implementation of interim targets would help to minimise air pollution in specific locations.
The implementation of air quality standards for PM2.5 in the European Union (EU), United States (US), and other countries with high PM2.5 levels could prevent millions of premature deaths per year. The benefits of the US Clean Air Act from 1970 to 1990 were estimated at a central value of $22.2 trillion, compared to implementation costs of $0.52 trillion. Similarly, strategies for waste reduction, waste separation, recycling, and reuse, as well as improved methods of biological waste management, can help to reduce ambient air pollution.
In addition to the health benefits, achieving air pollution control targets can also have economic benefits. For example, China's war on pollution has resulted in a 3.2% decrease in pollution in areas near automated monitors, demonstrating the potential for technology-aided monitoring to improve enforcement and achieve pollution control targets.
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Particulate matter (PM) guidelines
Particulate matter (PM) is a common proxy indicator for air pollution. The major components of PM are sulfates, nitrates, ammonia, sodium chloride, black carbon, mineral dust, and water. PM is primarily generated by fuel combustion in different sectors, including transport, energy, households, industry, and agriculture.
PM is associated with several negative health impacts. In 2019, exposure to fine particulate matter was estimated to cause 4.2 million premature deaths worldwide per year. The mortality is due to cardiovascular and respiratory diseases, and cancers. WHO estimates that in 2019, about 68% of outdoor air pollution-related premature deaths were due to ischaemic heart disease and stroke, 14% were due to chronic obstructive pulmonary disease, 14% were due to acute lower respiratory infections, and 4% of deaths were due to lung cancers.
The World Health Organization's Air quality guidelines (AQG) serve as a global target for national, regional, and city governments to work towards improving their citizens' health by reducing air pollution. While the guidelines are neither standards nor legally binding criteria, they are designed to offer guidance in reducing the health impacts of air pollution based on expert evaluation of current scientific evidence. These guidelines incorporate scientific evidence from multiple countries, making them relevant to diverse conditions around the world and capable of supporting a broad range of policy options for air quality management.
The WHO's new guidelines recommend air quality levels for six pollutants, including PM, where evidence has advanced the most on health effects from exposure. The guidelines also highlight good practices for the management of certain types of PM, such as black carbon/elemental carbon, ultrafine particles, and particles originating from sand and dust storms. The health risks associated with PM equal to or smaller than 10 and 2.5 microns (µm) in diameter (PM10 and PM2.5, respectively) are of particular public health relevance. Both PM2.5 and PM10 are capable of penetrating deep into the lungs, but PM2.5 can even enter the bloodstream, primarily resulting in cardiovascular and respiratory impacts, and also affecting other organs.
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Ozone (O3) guidelines
Ozone (O3) is a major constituent of photochemical smog and is formed through the reaction with gases in the presence of sunlight. The World Health Organization (WHO) has developed air quality guidelines (AQG) to provide global targets for governments at all levels to improve the health of their citizens by reducing air pollution. The guidelines are based on expert evaluations of current scientific evidence and are designed to reduce the health impacts of air pollution. They are neither standards nor legally binding criteria, but they offer guidance and support for a broad range of policy options for air quality management.
The 2021 update to the WHO AQG was in response to the ongoing threat of air pollution to public health. The guidelines recommend levels and interim targets for common air pollutants, including O3. While the guidelines are not legally binding, they are intended to influence air quality policies worldwide. The recommended peak season mean 8-hour ozone concentration is 60 µg/m3. This is a significant reduction from the 2005 guideline, which did not provide a recommendation for long-term ozone concentrations.
The WHO recognizes that air pollution is a significant environmental threat to health and a leading cause of non-communicable diseases (NCDs) such as heart attacks, stroke, chronic obstructive pulmonary disease, asthma, and cancer. According to the WHO, there are approximately 7 million premature deaths annually due to the combined effects of outdoor and household air pollution. The guidelines aim to reduce these health impacts by providing targets for policy-makers to improve air quality.
The AQG also offer qualitative statements on the management of certain types of particulate matter (PM), such as black carbon/elemental carbon, ultrafine particles, and particles from sand and dust storms. These statements are based on the recognition that air pollution has significant health impacts and that interventions can provide multiple potential benefits. The guidelines are part of WHO's efforts to support countries in protecting public health through evidence-based policies and actions.
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Nitrogen dioxide (NO2) guidelines
Nitrogen dioxide (NO2) is one of the six pollutants considered harmful to public health and the environment. The other five pollutants are ozone, particulate matter, carbon monoxide, sulfur dioxide, and lead. The Clean Air Act requires the EPA to set national ambient air quality standards (NAAQS) for nitrogen oxides to address this issue.
In 1997, the WHO proposed an annual guideline value for outdoor nitrogen dioxide of 40 μg/m3 (0.023 ppm). This value was based on the Hasselblad meta-analysis, which found that significant adverse health effects occur at levels of 28.2 μg/m3 (0.015 ppm) or more. The WHO's guideline aimed to prevent the most severe exposures to nitrogen dioxide, which can have harmful effects on respiratory health, particularly in children.
Several studies have investigated the health impacts of nitrogen dioxide exposure. One study found that a 30 μg/m3 increase in nitrogen dioxide levels was associated with a 20% increased risk of respiratory symptoms in children under 12 years of age. Another study reviewed the health effects of indoor gas appliances, which can emit nitrogen dioxide, and found respiratory symptoms such as wheeze, cough, chest infections, shortness of breath, and bronchitis. These studies have contributed to the development of guidelines for indoor and outdoor air quality by the WHO.
It is important to note that while the WHO provides global guidance on air pollutant thresholds and limits, they are not legally binding criteria. However, they offer valuable recommendations to reduce the health impacts of air pollution. Implementing air quality standards can have significant public health benefits, as evidenced by the estimated $22.2 trillion in benefits from the US Clean Air Act from 1970 to 1990.
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Sulfur dioxide (SO2) guidelines
Sulfur dioxide (SO2) is one of the six pollutants that the Clean Air Act requires the US Environmental Protection Agency (EPA) to set national ambient air quality standards (NAAQS) for. The other pollutants are ozone (O3), particulate matter (PM2.5 and PM10), nitrogen dioxide (NO2), carbon monoxide (CO), and lead. The EPA is also required to periodically review and update these standards to ensure they provide adequate health and environmental protection.
The World Health Organization (WHO) has also established air quality guidelines (AQG) for sulfur dioxide, among other pollutants. These guidelines are not legally binding but are designed to offer guidance to policy-makers in reducing the health impacts of air pollution. They are based on expert evaluations of scientific evidence from multiple countries, making them relevant to diverse conditions and capable of supporting a broad range of policy options for air quality management.
The WHO's AQGs serve as a global target for national, regional, and city governments to strive toward improving their citizens' health by reducing air pollution. According to the WHO, air pollution is the greatest environmental threat to health and is a leading cause of non-communicable diseases (NCDs) such as heart attacks, strokes, chronic obstructive pulmonary disease (COPD), asthma, and cancer. In 2019, 99% of the world's population lived in areas that did not meet the WHO's AQG levels, and air pollution was associated with 6.7 million premature deaths annually.
To reduce sulfur dioxide emissions, the WHO recommends policies supporting cleaner transport, energy-efficient homes, power generation, industry, and better municipal waste management. For example, the capture of methane gas emitted from waste sites as an alternative to incineration can reduce sulfur dioxide emissions. Additionally, the use of cleaner fuels with reduced sulfur content can also help decrease sulfur dioxide levels in the atmosphere.
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Frequently asked questions
The World Health Organization (WHO) air quality guidelines offer global guidance on thresholds and limits for key air pollutants that pose health risks. The guidelines are developed through a transparent, evidence-based decision-making process.
The guidelines provide recommendations for the following pollutants: particulate matter (PM2.5 and PM10), ozone (O3), nitrogen dioxide (NO2), sulfur dioxide (SO2), and carbon monoxide (CO). For example, the guidelines suggest that PM2.5 should not exceed 5 μg/m3 as an annual mean.
The WHO first released the air quality guidelines in 1987 and has since updated them in 1997 and 2021. The latest update, released in 2021, adjusted the guidelines for several pollutants, including halving the guideline value for PM2.5.
No, the WHO air quality guidelines are not legally binding. They are intended to provide global guidance and reduce the health impacts of air pollution. However, they are not standards or criteria that countries are required to meet.
