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Air pollution is the world’s largest environmental risk to health,1 and a major cause of disease and premature death.2

Ambient (outdoor) and household (indoor) air pollution both contribute to the global burden. Emissions from transport, industry, power generation and agricultural processes affect both cities and rural areas and, according to estimates from the World Health Organization, 9 out of 10 of people worldwide breathe polluted air.2

Within the home, 3 billion people are at risk of household air pollution from use of unclean fuels and technologies for cooking and heating.3

Several common pollutants are harmful to health. However, ambient particulate matter  a complex mixture of solid and liquid particles suspended in air  is of particular concern, and levels of particulate matter are a key indicator of air quality and health risk.4

The respiratory system, as the first point of contact with inhaled pollutants, is uniquely vulnerable, but air pollution also affects the cardiovascular system and other aspects of health.5 Studies are continuing to identify causal associations of air pollutants with adverse health outcomes, and to uncover plausible biological mechanisms for these effects. The impact of air pollution on quality of life,6 and the effects of climate change on air pollution and health, are other important areas of study.

Here, The Clean Breathing Institute discusses the global burden of air pollution and the effects of air pollution on respiratory health.


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Air pollution mainly results from human activity and is a complex mix of solid, liquid and gas particles from both ambient (outdoor) and household (indoor) sources.5,7 Ambient sources include combustion of fossil fuels, road traffic and industry. Household sources can include fuels such as biomass, coal and kerosene used for cooking, heating and lighting.5,7 Important gaseous pollutants include volatile organic compounds (VOCs) such as benzene.Indoor sources of VOCs include construction materials, furnishing, paints, glues, heating appliances, tobacco smoke and cleaning products.Air pollution can also arise from natural sources such as dust, pollen and wildfires.5,9

Air pollution is a mixture of solid, liquid and gas particles suspended in the air4,9 and may include components such as ozone, nitrogen oxides, carbon monoxide and sulphur dioxide, metals, organic chemicals and biological materials.5,9

Particulate matter is used as an indicator of air pollution and is usually divided into groups based on particle size (Figure 1):5,9–12


  • Coarse particulate matter has an aerodynamic diameter of between 10 μm and 2.5 μm, and is referred to as PM10–2.5
  • Fine particulate matter has an aerodynamic diameter of less than 2.5 μm and is referred to as PM2.5
  • Ultrafine particulate matter has an aerodynamic diameter of less than 0.1 μm and is referred to as PM0.1


Fine (PM2.5) and ultrafine (PM0.1) particulate matter are associated with the greatest health risks, as they can travel deeper into the airways, reaching distal regions of the lungs, where water-soluble components can enter the bloodstream by translocating through alveolar capillaries (Figure 1).11,12  PM2.5 is commonly used as an indicator of global air pollution by organisations such as the World Health Organization.4


Particulate matter

Figure 1. Particulate matter in air pollution.5,10–21 


Global burden of air pollution

Ambient (outdoor) and household (indoor) air pollution cause an estimated 7 million premature deaths each year,22 including approximately 600,000 deaths per year in children under 5 years of age.23 Outside the home, incineration and combustion of fossil fuels emit a complex array of pollutants, including particulate matter, nitrogen dioxide, sulphur dioxide and carbon monoxide, which may react in the air to generate secondary pollutants, such as ground-level ozone. In 2016, 91% of the global population lived in places that did not meet the World Health Organization’s (WHO) air quality guideline levels for particulate matter,4 and more than 50% lived in cities with at least 2.5 times the recommended levels of fine particulate matter.24 The latest air quality data from over 100 countries can be viewed on the WHO interactive map.25

Ambient air pollution

Exposure to ambient air pollution was estimated to cause 4.2 million premature deaths worldwide in 2016.4 In 2015, the Global Burden of Diseases study identified ambient PM2.5 (particulate matter with diameter <2.5 μm) as responsible for 7.6% of total global mortality ─ this makes it the fifth most important global risk factor for death.26  

Ambient air pollution affects all geographical regions and countries, and people of all socioeconomic groups.22 However, low- and middle-income (LMI) countries are the most affected, with the poorest air quality in Eastern Mediterranean and African regions.24 In 2016, 91% of deaths linked to ambient air pollution occurred in LMI countries, with the highest numbers in South-East Asia and Western Pacific regions.4

Household air pollution

Household air pollution is another major cause of premature death. Around 3 billion people still cook using solid fuels or kerosene in inefficient stoves or open hearths.3 This releases particulate matter, methane, carbon monoxide, polyaromatic hydrocarbons and volatile organic compounds into the home,27 and also contributes to ambient air pollution. Each year, 3.8 million people die prematurely as a result of household air pollution.3

Household air pollution from cooking fuels is strongly linked to poverty, with rural households in Sub-Saharan Africa, South and East Asia and the Western Pacific experiencing the greatest health burden.27 This interactive graph28 shows mortality from household and ambient air pollution in WHO regions and countries.



Impact of air pollution on health

The effects of ambient (outdoor) and household (indoor) air pollution on human health are wide-ranging. Inhalation of airborne pollutants damages the respiratory tract, reduces lung function, and causes or exacerbates acute and chronic respiratory diseases, including asthma.More than 25% of premature deaths associated with air pollution are respiratory in nature.12


Outdoor air pollution and particulate matter are classed as carcinogenic to humans29 and exposure to air pollution is estimated to cause 29% of all adult deaths from lung cancer.2 It is estimated that air pollution causes 43% of all adult deaths from chronic obstructive pulmonary disease, 25% from stroke and 24% from heart disease.2 Household air pollution is responsible for nearly half (45%) of all pneumonia deaths in children under 5 years of age and contributes to 28% of pneumonia deaths in adults.3 There is mounting evidence for the adverse effects of prenatal exposure to air pollution on lung development, respiratory health and development of chronic disease in adulthood.30 BreatheLife – a joint campaign led by the World Health Organization (WHO), United Nations Environment, and Climate & Clean Air Coalition – provides tips on reducing prenatal exposure.31

In recent years, evidence for effects of inhaled pollutants on the central nervous system has also emerged. Exposure to air pollution has been associated with impaired cognitive and psychomotor development in children, and with cognitive decline and dementia in the elderly.32

Click here to learn more about the mechanisms through which air pollution leads to adverse health effects.

Why breathing clean air is important

Life-time exposure to ambient air pollution, in a highly polluted city such as Beijing in China, may result in an estimated loss of life expectancy of approximately 3 years.33,34 Other estimates suggest that long-term exposure to air pollution may reduce life expectancy by as much as 11 years (based on WHO consensus estimates for the mortality risk ratio related to an annual PM2.5 increase of 10 μg/m3).35

By reducing air pollution in cities to WHO air quality guideline levels (PM2.5 annual mean concentrations reduced to 10 μg/m3), air pollution-related deaths could be reduced by 15%.4

The Energy Policy Institute at the University of Chicago have estimated the extra life gained per person if air pollution in major cities met WHO air quality guideline levels:36



United Kingdom


<1 month

United States

US flag

1.6 months


Poland flag

1.3 years


China flag

3 years


India flag

4 years 


Evidence for health impacts of common air pollutants

Particulate matter

There is a well-documented causal link between exposure to particulate matter (especially PM2.5) and cardiorespiratory health outcomes and mortality, although effect sizes vary across studies, location and season.37 In a meta-analysis of the effects of short-term exposure to PM2.5 constituents, the strongest associations with mortality were observed for elemental carbon and potassium.37 Studies are uncovering the biological mechanisms for the effects of particulate matter on cardiorespiratory health, including modulation of the airway epithelium and induction of specific cytokine pathways in asthma,38 promotion of oxidative stress in atherosclerosis,13 and mechanisms relating to cell death.39  

Ground-level ozone

Ground-level ozone (O3), a constituent of photochemical smog, can cause breathing problems, trigger asthma, reduce lung function and cause lung diseases.4 Short-term exposure is associated with mortality and hospitalisation, and there is growing evidence for the effects of long-term exposure on respiratory and cardiorespiratory mortality in warm-season months.40 Ozone exposure may also have metabolic effects.41

Nitrogen dioxide

Short- and long-term exposure to nitrogen dioxide (NO2) has been associated with mortality, hospital admissions and respiratory symptoms, including among asthmatic children.42,43 However, it is difficult to identify a direct effect of NO2 exposure due to its strong correlation with other air pollutants.43  

Sulphur dioxide

Sulphur dioxide (SO2) can inflame the respiratory tract, affect lung function, and irritate the eyes; changes in lung function and respiratory symptoms may arise in people with asthma after just 10 minutes of exposure.4 SO2 has also been associated with cardiac disease hospitalisation and mortality.4

Co-exposure to pollutants

Alongside studies of individual pollutants, there are increasing efforts to understand the real-world complexity of the interactive effects of exposure to more than one inhalent – for example, effects of co-exposure to air pollutants plus aeroallergens on respiratory tract function.44,45 The interaction of physical activity and air pollution on cardiorespiratory health,46,47 and effects of climate change on air quality and health,40 are further areas of current study. 


Impact of air pollution on quality of life (QoL)

Clean air is a basic human requirement. Air quality and risk to health can affect physical, mental, and social well-being,6 although further studies are needed to fully elucidate the impact of air pollution on QoL. Health-related QoL is impacted by pollution-related symptoms, diseases, and exacerbations of existing respiratory conditions.48–50 Beyond the physical effects, studies have shown that air quality is an important determinant of subjective well-being, which encompasses individuals’ life satisfaction, happiness and optimism.6 Exposure to air pollution has been linked to impaired subjective well-being.51–57

Daily life is also affected - air pollution has been associated with reduced productivity,58,59 lower daily activity scores and lower social functioning,49 and may entail avoidance of physical outdoor activity to limit exposure. Pollution-induces cognitive deficits in children and adults60 and this may further impact QoL.

Download our literature review and our advisory meeting summary to find out more about the global burden of air pollution and the effects of air pollution on respiratory health.



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man with mask


When avoiding air pollution is difficult, introducing measures to prevent the effects of air pollution and minimise respiratory symptoms can help.


group of doctors


The respiratory tract is our first line of defence against pollution. So when pollutants stop it from doing its job, some people are at greater risk than others.