Ambient Air Pollution: A Silent Killer

Ambient air pollution is a pressing issue that affects people worldwide. In 2019, it was deemed the largest environmental risk to health, causing approximately 4.2 million premature deaths annually. According to the World Health Organization (WHO), 99% of the global population breathes air that exceeds their guideline limits on pollutant levels. This issue is particularly severe in low- and middle-income countries, where 89% of premature deaths related to outdoor air pollution occur. WHO works with countries to address this issue, focusing on knowledge, institutional capacity building, and leadership. They also maintain an Ambient Air Quality Database that compiles ground measurements of pollutants like nitrogen dioxide and particulate matter. Successful policies to combat ambient air pollution include cleaner technologies, improved waste management, access to clean household energy, and promoting sustainable transport options.

Health risks and effects

Ambient air pollution is a major environmental health problem affecting people in low-, middle-, and high-income countries. It is the second-highest risk factor for non-communicable diseases, and it is the single largest environmental health risk in Europe. According to the World Health Organization (WHO), ambient air pollution in both cities and rural areas caused an estimated 4.2 million premature deaths worldwide per year in 2019. This number was 4.2 million in 2016 as well. About 88% of these deaths occurred in low- and middle-income countries.

The health impacts of exposure to ambient air pollution depend on the types and concentrations of the pollutants in the air. Fine particulate matter (PM2.5) is a common and critical pollutant that leads to negative health outcomes. These particles are less than 2.5 micrometres in diameter and can lodge deeply into the lungs. They can also enter the bloodstream and travel to organs, causing systemic damage to tissues and cells. The adverse health effects of particulate air pollution, even at relatively low levels, remain a global public concern.

The main pathway of exposure to air pollution is through the respiratory tract. Breathing in these pollutants leads to inflammation, oxidative stress, immunosuppression, and mutagenicity in cells throughout the body, impacting the lungs, heart, and brain, among other organs. Almost every organ in the body can be affected by air pollution. Exposure to air pollution, especially long-term exposure, increases the risk of respiratory infections, heart disease, stroke, and lung cancer. Emerging evidence suggests that exposure to ambient air pollution may also cause cerebrovascular, neurodevelopmental, and neuropsychiatric disorders, adverse pregnancy outcomes, other cancers, diabetes, cognitive impairment, and neurological diseases.

Children, the elderly, and people in low socioeconomic communities are more susceptible to the health impacts of air pollution. People who are already ill are also more vulnerable to the adverse effects of air pollution. The health risks and disease pathways between ambient and household air pollution exposure are often similar due to their comparable compositions. Additional safety risks are associated with the fuels and technologies used in households that emit air pollution.

To address the health risks posed by ambient air pollution, the WHO's Air Quality and Health Unit works in three key areas: knowledge, evidence, and measuring progress; institutional capacity building and technical support; and leadership and coordination. The WHO also provides global guidance on thresholds and limits for key air pollutants through its Global Air Quality Guidelines (AQG). These guidelines are developed through a transparent, evidence-based decision-making process and offer interim targets to promote a gradual shift towards lower pollutant concentrations.

Reducing air pollution levels

Air pollution is a major environmental health problem, causing an estimated 4.2 million premature deaths worldwide in 2019. The World Health Organization (WHO) considers air pollution a public health emergency and has invited governments, agencies, and organizations to pledge to reduce the health impacts of air pollution by 50% by 2040.

Industry and Energy

• Implement clean technologies to reduce industrial smokestack emissions.
• Improve the management of urban and agricultural waste, including capturing methane gas emitted from waste sites as an alternative to incineration (for use as biogas).
• Increase the use of low-emissions fuels and renewable, combustion-free power sources, such as solar and wind energy.
• Provide access to affordable clean household energy solutions for cooking, heating, and lighting.

Transport

• Shift to cleaner modes of power generation, such as electric vehicles and low-emissions fuels, including fuels with reduced sulfur content.
• Prioritize rapid urban transit, walking, and cycling networks in cities, as well as interurban rail travel for freight and passengers.
• Reduce emissions from vehicles and engines through stringent emission standards and cleaner-burning gasoline.

Urban Planning

• Improve the energy efficiency of buildings and make cities more green and compact, thereby reducing their carbon footprint.
• Plant and care for trees, as they filter pollutants, absorb carbon dioxide, and release oxygen into the atmosphere.

Individual Actions

• Limit energy consumption by using energy-efficient appliances and heating systems, turning off electrical items when not in use, and using a programmable thermostat.
• Choose sustainable products and reduce exposure to chemicals, especially those containing volatile organic compounds (VOCs) and particulate matter (PM).
• Opt for walking, cycling, or public transportation instead of driving whenever possible, and limit idling your vehicle.
• Support local initiatives and advocate for policies that promote clean air and sustainable practices.

Cleaner transport and energy-efficient homes

Ambient air pollution, combined with household air pollution, is associated with 6.7 million premature deaths annually, with 4.2 million of these occurring in 2019. The World Health Organization (WHO) considers air pollution a public health emergency and has invited governments, agencies, and organizations to take voluntary actions to reduce the health impacts of air pollution by 50% by 2040.

To address this, the WHO's Air Quality and Health Unit works in three cross-cutting areas: knowledge, evidence, and measuring progress; institutional capacity building and technical support; and leadership and coordination. Member States and sub-national entities are responsible for implementing and monitoring policies to promote air quality for health, which requires coordinated action between various stakeholders and sectors.

One of the successful policies to reduce air pollution is to promote cleaner transport and energy-efficient homes. Here are some ways to achieve this:

Cleaner Transport

• Shifting to cleaner modes of power generation, such as renewable, combustion-free power sources like solar, wind, or hydropower.
• Prioritizing rapid urban transit, walking, and cycling networks in cities, as well as interurban rail freight and passenger travel.
• Adopting cleaner heavy-duty diesel vehicles and low-emission vehicles and fuels, including fuels with reduced sulfur content.
• Improving fuel efficiency standards for passenger vehicles, heavy-duty trucks, and buses to cut carbon pollution and improve energy security.
• Encouraging the use of electric vehicles and reducing the use of cars, especially those with idling engines, as vehicle exhaust is a major source of air pollution.

Energy-Efficient Homes

• Improving the energy efficiency of buildings by using efficient appliances and heating systems, as well as better insulation.
• Transitioning to cleaner household fuels for cooking, heating, and lighting, such as affordable, clean household energy solutions.
• Reducing the use of polluting fuels like kerosene, wood, and coal for residential heating and cooking, which contribute to millions of deaths each year.
• Promoting the use of electric or hand-powered lawn equipment instead of gas-powered engines, as they often lack pollution control devices.

Policy implementation and monitoring

Policy Implementation

The implementation of policies to improve air quality and protect public health is primarily the responsibility of Member States and sub-national entities, as per WHO guidelines. Effective policies require coordinated action from various sectors and stakeholders, including cooperation with other UN agencies and non-state actors.

Successful policy implementation strategies include:

• Sustainable land use practices: This involves promoting cleaner household energy sources and sustainable transport options, such as electric vehicles and improved public transportation.
• Energy-efficient housing: Encouraging the use of renewable and low-emission energy sources for heating, lighting, and cooking can reduce household air pollution.
• Cleaner industry and waste management: Adopting clean technologies in industries can reduce smokestack emissions. Additionally, improving waste management practices, such as capturing methane gas from waste sites, can mitigate pollution.
• Greener power generation: Increasing the use of renewable and low-emission power sources, such as solar energy, helps reduce air pollution.
• Urban planning: Making cities more compact and energy-efficient, as well as promoting green spaces, can improve air quality in urban areas.

Monitoring and Evaluation

Monitoring air quality and evaluating the effectiveness of implemented policies are essential for addressing ambient air pollution. WHO has developed the Ambient Air Quality Database, which compiles ground measurements of air pollutants, particularly nitrogen dioxide (NO2) and particulate matter (PM) with diameters of 10 μm (PM10) or 2.5 μm (PM2.5). This database is regularly updated and provides critical information for global assessments and policy advocacy.

To ensure accurate monitoring, it is important to consider the following:

• Monitor placement: Monitors should reflect exposures over a wide area and not be influenced by a single source of pollution, such as a power plant or highway.
• Data availability: Currently, PM and NO2 data are more readily available for larger cities, but efforts are made to include measurements from smaller agglomerations and rural areas as well.
• Modelling estimates: In areas without ground monitors, WHO uses modelled estimates based on information from the Ambient Air Quality Database to assess air quality.

By combining robust data collection with effective policy implementation, WHO, along with national and local governments, can make significant progress in reducing ambient air pollution and protecting the health of people worldwide.

Global trends and changes

Ambient air pollution is a major environmental health problem affecting everyone in low-, middle-, and high-income countries. According to the World Health Organization (WHO), 99% of the world's population lives in places where air pollution levels exceed WHO guideline limits. This is supported by another source that states that 9 out of 10 people breathe air containing high levels of pollutants.

In 2019, air pollution, including ambient and household air pollution, was the largest environmental risk to health, causing about 6.7 million premature deaths annually. Of these, 4.2 million were attributed to ambient air pollution alone, with 89% of these premature deaths occurring in low- and middle-income countries. The greatest burden is found in the WHO South-East Asia and Western Pacific Regions.

Outdoor air pollution in both cities and rural areas is estimated to cause 4.2 million premature deaths worldwide per year. This mortality is due to exposure to fine particulate matter, which results in strokes, heart diseases, lung cancer, acute and chronic respiratory diseases, and other illnesses.

There have been some improvements in reducing air pollution globally. Since 1990, death rates from total air pollution have nearly halved, although this decline has been primarily driven by improvements in indoor air pollution. Death rates from outdoor air pollution have seen much more modest improvements.

To address ambient air pollution, the WHO has set guidelines and targets for key air pollutants that pose health risks. These guidelines are developed through a transparent, evidence-based decision-making process and provide interim targets to promote a gradual shift from high to lower pollutant concentrations. For example, achieving interim target one (35 µg/m3) would save around 300,000 deaths annually worldwide.

The WHO also works with countries to monitor air pollution and improve air quality through policies and investments that support sustainable land use, cleaner household energy and transport, energy-efficient housing, power generation, industry, and better municipal waste management. Additionally, the WHO provides technical support to its member states in developing normative guidance, tools, and authoritative advice on health issues related to air pollution and its sources.

Frequently asked questions