Outdoor Air Pollution: Who Suffers?

Outdoor air pollution is a leading environmental risk factor affecting populations worldwide, causing an estimated 4.2 million premature deaths in 2019. It is caused by the presence of substances in the air at higher concentrations than their natural levels, with sources including residential energy, vehicles, power generation, industry, and agriculture. Outdoor air pollution is closely linked to climate and ecosystems and is a major health and environmental problem that affects people in low-, middle-, and high-income countries. WHO is working with countries to monitor and improve air quality through interventions and initiatives for healthy sectoral policies.

Outdoor air pollution is a major environmental health problem

Outdoor air pollution is a pressing issue that poses significant risks to human health and the environment. It is a leading environmental risk factor affecting populations worldwide, causing an estimated 4.2 million premature deaths annually, according to the World Health Organization (WHO). The problem is particularly acute in low- and middle-income countries, where 89% of these premature deaths occur.

The sources of outdoor air pollution are diverse and context-specific. They include residential energy use for cooking and heating, vehicle emissions, power generation, waste incineration, and industrial activities. Fine particulate matter, a product of these pollution sources, has detrimental health effects, including strokes, heart diseases, lung cancer, and acute and chronic respiratory diseases. Short-term exposure to elevated levels of air pollution can also lead to adverse outcomes such as impacts on lung function, exacerbation of asthma, and increased hospital admissions for respiratory and cardiovascular issues.

Particulate matter (PM) is a critical indicator of air pollution, encompassing sulfates, nitrates, ammonia, sodium chloride, black carbon, mineral dust, and water. Other harmful pollutants include ozone (O3), nitrogen dioxide (NO2), and carbon monoxide (CO), an odourless and colourless toxic gas released from the incomplete combustion of fuels. These pollutants have far-reaching health consequences, with 99% of the global population breathing air that exceeds WHO guideline limits.

Addressing outdoor air pollution requires concerted action by policymakers at various levels. Successful policies have been implemented in sectors such as transport, energy, waste management, and urban planning. For example, promoting clean technologies, improving waste management practices, transitioning to cleaner vehicles and fuels, and increasing the energy efficiency of buildings can significantly reduce outdoor air pollution.

The WHO actively supports initiatives to improve air quality and mitigate the health risks associated with air pollution. They provide technical assistance, guidance, and advice to member states while also monitoring global trends and reporting on the outcomes of actions taken to tackle this pressing issue.

Fine particulate matter causes strokes, heart disease, lung cancer, and respiratory diseases

Outdoor air pollution is a significant environmental health problem, causing an estimated 4.2 million premature deaths worldwide in 2019. Fine particulate matter (PM), a major component of air pollution, has been linked to strokes, heart disease, lung cancer, and respiratory diseases.

PM is a mix of tiny solid and liquid particles suspended in the air we breathe. These particles vary in size, with some being one-tenth the diameter of a strand of hair, while others are even smaller and can only be seen under an electron microscope. Fine particles (PM2.5) are the main cause of reduced visibility (haze) and can be carried over long distances by wind, eventually settling on the ground or water. The major components of PM are sulfates, nitrates, ammonia, sodium chloride, black carbon, mineral dust, and water.

Numerous epidemiological, biomedical, and clinical studies have found a strong association between exposure to PM and an increased risk of cardiovascular disease. The molecular mechanisms by which PM causes cardiovascular disease include direct toxicity to the cardiovascular system or indirect injury by inducing systemic inflammation and oxidative stress in peripheral circulation. Short-term exposure to PM has been linked to triggering CVD-related events, especially in susceptible individuals such as the elderly or those with pre-existing coronary artery disease.

Fine particulate matter has also been linked to an increased risk of strokes. Studies have shown that exposure to PM alters cerebral hemodynamics in the elderly and is associated with hospital admissions for ischemic and hemorrhagic strokes and transient ischemic attacks.

In addition to cardiovascular and cerebrovascular effects, PM exposure has been linked to respiratory symptoms such as irritation of the airways, coughing, or difficulty breathing. People with pre-existing heart or lung diseases, children, older adults, and minority populations are more likely to be affected by particle pollution exposure due to increased sensitivity or higher exposure levels.

Lung cancer has also been associated with exposure to fine particulate matter. A 2022 public health study in seven Western European countries found a strong association between long-term exposure to very low levels of PM2.5 and lung cancer mortality.

Common sources of outdoor air pollution include vehicles, power generation, and industry

Outdoor air pollution is a major environmental health problem affecting everyone in low-, middle-, and high-income countries. It is estimated to have caused 4.2 million premature deaths worldwide in 2019, with 89% of those premature deaths occurring in low- and middle-income countries. The greatest number of deaths were in the WHO South-East Asia and Western Pacific Regions.

Secondly, power generation, particularly coal-fueled power plants, is a major source of air pollution. The combustion of fossil fuels, such as coal, releases hazardous substances and greenhouse gases, including carbon dioxide, nitrogen oxides, and sulfur oxides. Additionally, power generation can produce polycyclic aromatic hydrocarbons (PAHs) as by-products, which are organic compounds containing carbon and hydrogen and are known to have negative health effects.

Lastly, industrial facilities and processes are significant contributors to outdoor air pollution. Industries often release pollutants through industrial smokestacks, including particulate matter, nitrogen dioxide, and sulfur dioxide. Certain industrial processes, such as iron, steel, and rubber product manufacturing, can also produce PAHs. Additionally, the combustion of industrial fuels can release carbon monoxide, a toxic gas that is harmful to human health.

Addressing these sources of outdoor air pollution requires concerted action by local, national, and regional policymakers. Successful policies include promoting clean technologies, improving waste management practices, transitioning to cleaner modes of transportation and power generation, and improving energy efficiency in buildings. These interventions not only reduce air pollution but also offer public health and wellbeing co-benefits.

Outdoor air pollution is caused by pollutants such as sulfates, nitrates, ammonia, and black carbon

Outdoor air pollution is a pressing global issue that adversely affects human health and the environment. It is caused by various pollutants, including sulfates, nitrates, ammonia, and black carbon, which are released into the atmosphere through human activities and natural processes. These pollutants have severe health impacts, contributing to the approximately 4.2 million premature deaths recorded worldwide in 2019.

Sulfates, scientifically known as sulfur dioxide (SO2), are primary air pollutants emitted directly into the environment. They are produced mainly through the combustion of fossil fuels and biomass fuels. Sulfates are a major component of particulate matter (PM), specifically PM2.5, which also includes other pollutants like nitrates and ammonia. PM2.5, due to its small particle size, can be easily inhaled, leading to adverse health effects.

Nitrates, or nitrogen dioxide (NO2), are another pollutant contributing to outdoor air pollution. They are commonly released from the combustion of fuels in the transportation and industrial sectors. Nitrates, along with other nitrogen oxides (NOx), also contribute to the formation of ground-level ozone (O3), a major constituent of smog. Exposure to ozone can cause respiratory problems, trigger asthma, reduce lung function, and lead to lung disease.

Ammonia (NH3) is also a significant contributor to outdoor air pollution. It is often released into the atmosphere through agricultural practices, such as fertilizer use, and livestock waste. Ammonia, in combination with other pollutants, can lead to the formation of fine particulate matter, which has adverse health effects.

Black carbon, a component of PM2.5, is another critical pollutant. It is sometimes referred to as soot and is produced through the incomplete combustion of fossil fuels, biofuels, and biomass. Black carbon can be emitted from both anthropogenic sources, such as diesel vehicles, and natural sources, like wildfires. Exposure to black carbon has been associated with cardiovascular health issues and premature mortality.

These pollutants, released into the outdoor air, have severe consequences for human health and the environment. The World Health Organization (WHO) has recognized the urgency of addressing air pollution, especially in low- and middle-income countries, where the majority of premature deaths occur. By managing these pollutants and implementing cleaner technologies, we can mitigate the harmful impacts of outdoor air pollution on a global scale.

WHO provides technical support and guidance to member states to address outdoor air pollution

Outdoor air pollution is a leading environmental risk factor that affects populations worldwide, causing an estimated 4.2 million premature deaths in 2019, with 68% of these being due to ischaemic heart disease and stroke. The World Health Organization (WHO) recognises the urgency of this issue and supports countries in protecting public health through evidence-based policies and actions.

WHO provides technical support and guidance to its member states to address outdoor air pollution. WHO's Air Quality and Health Unit works across three cross-cutting areas: knowledge, evidence and measuring progress; institutional capacity building; and technical support. WHO promotes interventions and initiatives for healthy sectoral policies, addressing key risks to health from outdoor air pollution and contributing to achieving health co-benefits from climate change mitigation policies.

WHO supports countries by providing evidence, building institutional capacity, and leveraging the health argument to bring different sectors together to tackle air pollution. WHO provides technical support to its member states in developing normative guidance, tools, and authoritative advice on health issues related to outdoor air pollution and its sources. WHO monitors and reports on global trends and changes in health outcomes associated with actions taken to address outdoor air pollution at the national, regional, and global levels.

WHO has also developed and implemented a strategy to raise awareness of the risks of outdoor air pollution and the solutions that can be implemented to mitigate these risks. WHO provides guidance on successful policies that reduce outdoor air pollution, such as clean technologies that reduce industrial smokestack emissions and improved management of urban and agricultural waste. WHO also promotes access to affordable clean household energy solutions for cooking, heating, and lighting, as well as the adoption of cleaner modes of power generation and transport.

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