Air Pollution: Protecting Our Health

Air pollution is a global health crisis, causing an estimated 4.2 million premature deaths worldwide each year. It is a complex mixture of solid particles, liquid droplets, and gases, with sources ranging from household fuel burning to industrial chimneys, traffic exhausts, and agricultural practices. To combat this, the World Health Organization (WHO) has developed the WHO Air Quality Guidelines, which offer guidance on reducing the health impacts of air pollution. These guidelines are based on scientific evidence from multiple countries and are designed to support a broad range of policy options for air quality management. While they are not legally binding, they serve as a crucial reference for governments and organizations worldwide, aiming to protect public health and improve air quality.

Air pollution sources

Air pollution is a complex mixture of solid particles, liquid droplets, and gases. It can come from many sources, including household fuel burning, industrial chimneys, traffic exhausts, power generation, open burning of waste, agricultural practices, desert dust, and many other sources. Different sources can lead to different mixtures of air pollution. For example, an urban city near the sea can have particulate matter consisting of sea salt, road dust, and smoke from diesel engines. In contrast, a rural area near a forest may have particulate matter consisting of soil, smoke from cookstoves, and forest fires.

The World Health Organization (WHO) has identified several key sources of air pollution that are of particular concern due to their impact on human health and the environment. These sources include:

• Household fuel burning: The combustion of fossil fuels and biomass in households can release harmful pollutants such as particulate matter (PM), nitrogen dioxide (NO2), and carbon monoxide (CO).
• Industrial chimneys: Industrial activities, such as factories and power plants, can emit a range of pollutants, including PM, NO2, sulfur dioxide (SO2), and volatile organic compounds (VOCs).
• Traffic exhausts: Vehicles, especially those powered by diesel and gasoline engines, release pollutants such as NO2, carbon dioxide (CO2), and PM.
• Power generation: The burning of fossil fuels for electricity generation can release large amounts of CO2, NOx, SO2, and mercury.
• Open burning of waste: The open burning of garbage and agricultural waste can release toxic pollutants such as dioxins, furans, and heavy metals.
• Agricultural practices: Agriculture can contribute to air pollution through ammonia emissions from livestock farming, pesticide use, and the release of greenhouse gases such as methane (CH4) and nitrous oxide (N2O).

Addressing these sources of air pollution is crucial to improving air quality and protecting public health. The WHO's Air Quality Guidelines AQG provide global targets and recommendations for reducing air pollution and improving air quality. These guidelines are regularly updated to incorporate the latest scientific evidence and research on the health impacts of air pollution. By implementing measures to reduce emissions from these sources and improve air quality, significant health benefits can be achieved, saving millions of lives globally.

Air quality guidelines

Air pollution is a complex mixture of solid particles, liquid droplets, and gases. It can come from many sources, including household fuel burning, industrial chimneys, traffic exhausts, power generation, open burning of waste, agricultural practices, desert dust, and many other sources. The World Health Organization (WHO) has developed global air quality guidelines (AQG) to offer guidance on reducing the health impacts of air pollution. These guidelines are not legally binding but are based on scientific evidence and designed to protect public health.

The first release of the guidelines was in 1987, and several updated versions have been published since then. The latest global version was released in 2005, and the guidelines were most recently updated in 2021. The 2021 update includes recommendations for annual mean concentrations of PM2.5 and PM10 (particles with an aerodynamic diameter of equal to or less than 2.5 and 10 micrometres, respectively) and nitrogen dioxide (NO2). It also includes targets for reducing exposure to pollutants such as ozone (O3), nitrogen dioxide (NO2), and sulfur dioxide (SO2). These targets are designed to promote a gradual shift from high to lower concentrations, reducing the health risks associated with air pollution.

The WHO Air quality guidelines are developed through a rigorous process that involves multiple expert groups. One group selects the pollutants to be updated, while other teams of experts draft background materials, including literature reviews and assessments. Based on these materials, another expert group agrees on the format and content of the updated guidelines and recommends changes. The guidelines are designed to be relevant to diverse conditions in all WHO regions and to support a broad range of policy options for air quality management.

The guidelines have significant implications for public health and economic welfare. Exposure to air pollution has been linked to various health problems, including cardiovascular and respiratory diseases, cancers, developmental delays in children, and psychological and behavioural problems. In 2019, ambient (outdoor) air pollution was estimated to have caused 4.2 million premature deaths worldwide, with a disproportionate impact on people in low- and middle-income countries. The economic benefits of improving air quality can be substantial, as seen in the US, China, and the EU, where the gains from reduced mortality, lower medical expenditures, and improved worker productivity far outweigh the costs of implementing clean air policies.

Health risks

Air pollution is one of the greatest environmental threats to human health, alongside climate change. It is the leading cause of non-communicable diseases (NCDs) such as heart attacks, stroke, lung cancer, and chronic obstructive pulmonary disease (COPD). According to the World Health Organization (WHO), air pollution causes around 7 million premature deaths each year, with millions more suffering ill health as a result. The majority of these premature deaths occur in low- and middle-income countries.

WHO's Air Quality and Health Unit works across three cross-cutting 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 health risks associated with particulate matter equal to or smaller than 10 and 2.5 microns (PM10 and PM2.5, respectively) in diameter are of particular concern. These particles are capable of penetrating deep into the lungs, with PM2.5 also able to enter the bloodstream, affecting all major organs. PM is primarily generated by fuel combustion in sectors such as transport, energy, households, industry, and agriculture.

Recent studies have also found an association between prenatal exposure to high levels of air pollution and developmental delays at age three, as well as psychological and behavioural problems later in life, including symptoms of attention deficit hyperactivity disorder (ADHD), anxiety, and depression.

In children, exposure to air pollution can cause reduced lung growth and function, respiratory infections, and aggravated asthma. For adults, ischaemic heart disease and stroke are the most common causes of premature death attributable to outdoor air pollution. There is also emerging evidence of other effects, such as diabetes and neurodegenerative conditions.

Policy options

The World Health Organization (WHO) Air Quality Guidelines (AQG) are a set of evidence-based recommendations for limit values of specific air pollutants. The guidelines are designed to help countries achieve air quality that protects public health. While the guidelines are not legally binding, they are intended to offer direction in reducing the health impacts of air pollution.

The guidelines are based on scientific evidence from multiple countries, making them relevant to diverse conditions worldwide. They are meant to support a wide range of policy options for air quality management. The guidelines include recommendations for reducing emissions from various sources, such as industry, transport, power generation, and agriculture. They also provide guidance on reducing concentrations of pollutants in the ambient air and reducing exposure of individuals and populations.

One important policy option is to prioritize the prevention of emissions and their reduction at the source. For example, clean technologies can reduce industrial smokestack emissions, and improved waste management can capture methane gas emitted from waste sites for use as biogas. Another option is to promote access to affordable clean household energy solutions for cooking, heating, and lighting.

Policies can also focus on urban planning, such as improving the energy efficiency of buildings and making cities more green and compact. Transport policies can prioritize rapid urban transit, walking, and cycling networks, as well as the adoption of cleaner vehicles and fuels. Additionally, the guidelines recommend increasing the use of low-emission fuels and renewable combustion-free power sources, such as solar and wind energy.

WHO also emphasizes the importance of health risk assessments in decision-making for emission reduction measures. These assessments provide estimates of the health impacts on the population, allowing for comparisons between different policy options. The guidelines offer valuable insights into the concentration-response relationships, helping technical experts and decision-makers understand the health consequences of certain regulations and standards.

Expert evaluations

The World Health Organization (WHO) has been developing air quality guidelines since 1987. The guidelines are informed by the best available scientific evidence and are designed to offer guidance in reducing the health impacts of air pollution. They are based on expert evaluations of current scientific evidence from multiple countries, making them relevant to diverse conditions around the world.

The guidelines are not legally binding, but they are intended to support a broad range of policy options for air quality management. They incorporate scientific evidence from multiple countries, making them applicable to diverse conditions in all WHO regions. The guidelines include recommended levels and interim targets for common air pollutants such as particulate matter (PM), ozone (O3), nitrogen dioxide (NO2), and sulfur dioxide (SO2).

The development of the guidelines involves several expert groups, each with a specific function. One group selects the pollutants to be updated, while other teams of experts draft the background material, including literature reviews and assessments. Another expert group then reviews and comments on the background materials and agrees on the format and content of the updated guidelines. The guidelines are updated regularly to ensure their continued relevance and to incorporate new health studies.

WHO's AirQ+ tool, launched in 2016, is designed to facilitate the assessment of the impact of air pollution and should be used with the support of an epidemiologist or air pollution impact assessment expert. It has been used in over 300 cities by more than 1000 users from 112 countries.

In 2023, WHO published a report highlighting emerging methods such as machine learning and geostatistical data fusion for monitoring air pollution levels and tracking the progress of air pollution reduction policies. This report provides an overview of the strengths and weaknesses of different measurement and modelling methods and is intended to support countries in understanding their baseline air quality levels and developing plans for air quality monitoring and data management.

Frequently asked questions