Air Pollution

air pollution image


    Air pollution is contamination of the indoor or outdoor environment by any chemical, physical or biological agent that modifies the natural characteristics of the atmosphere. Household combustion devices, motor vehicles, industrial facilities and forest fires are common sources of air pollution. Pollutants of major public health concern include particulate matter, carbon monoxide, ozone, nitrogen dioxide and sulfur dioxide. Outdoor and indoor air pollution cause respiratory and other diseases, which can be fatal.

    Disease Outbreak

    There is no Disease Outbreak data at this time

    Factsheet: Air pollution

    Key Facts

    • Around 3 billion people cook and heat their homes using open fires and simple stoves burning biomass (wood, animal dung and crop waste) and coal.
    • Over 4 million people die prematurely from illness attributable to the household air pollution from cooking with solid fuels.
    • More than 50% of premature deaths due to pneumonia among children under 5 are caused by the particulate matter (soot) inhaled from household air pollution.
    • 3.8 million premature deaths annually from noncommunicable diseases including stroke, ischaemic heart disease, chronic obstructive pulmonary disease (COPD) and lung cancer are attributed to exposure to household air pollution.


    Factsheet: Ambient (outdoor) air quality

    Key facts

    • Air pollution is a major environmental risk to health. By reducing air pollution levels, countries can reduce the burden of disease from stroke, heart disease, lung cancer, and both chronic and acute respiratory diseases, including asthma.
    • The lower the levels of air pollution, the better the cardiovascular and respiratory health of the population will be, both long- and short-term.
    • The "WHO Air quality guidelines" provide an assessment of health effects of air pollution and thresholds for health-harmful pollution levels.
    • In 2014, 92% of the world population was living in places where the WHO air quality guidelines levels were not met.
    • Ambient (outdoor air pollution) in both cities and rural areas was estimated to cause 3 million premature deaths worldwide in 2012.
    • Some 88% of those premature deaths occurred in low- and middle-income countries, and the greatest number in the WHO Western Pacific and South-East Asia regions.
    • Policies and investments supporting cleaner transport, energy-efficient housing, power generation, industry and better municipal waste management would reduce key sources of urban outdoor air pollution.
    • Reducing outdoor emissions from household coal and biomass energy systems, agricultural waste incineration, forest fires and certain agro-forestry activities (e.g. charcoal production) would reduce key rural and peri-urban air pollution sources in developing regions.
    • Reducing outdoor air pollution also reduces emissions of CO2 and short-lived climate pollutants such as black carbon particles and methane, thus contributing to the near- and long-term mitigation of climate change.
    • In addition to outdoor air pollution, indoor smoke is a serious health risk for some 3 billion people who cook and heat their homes with biomass fuels and coal.
    Household air pollution and health

    Indoor air pollution and household energy: the forgotten 3 billion

    Around 3 billion people still cook and heat their homes using solid fuels (i.e. wood, crop wastes, charcoal, coal and dung) in open fires and leaky stoves. Most are poor, and live in low- and middle-income countries.

    Such inefficient cooking fuels and technologies produce high levels of household air pollution with a range of health-damaging pollutants, including small soot particles that penetrate deep into the lungs. In poorly ventilated dwellings, indoor smoke can be 100 times higher than acceptable levels for fine particles. Exposure is particularly high among women and young children, who spend the most time near the domestic hearth.

    Impacts on health

    4.3 million people a year die prematurely from illness attributable to the household air pollution caused by the inefficient use of solid fuels (2012 data) for cooking. Among these deaths:

    • 12% are due to pneumonia
    • 34% from stroke
    • 26% from ischaemic heart disease
    • 22% from chronic obstructive pulmonary disease (COPD), and
    • 6% from lung cancer.

    Exposure to household air pollution almost doubles the risk for childhood pneumonia. Over half of deaths among children less than 5 years old from acute lower respiratory infections (ALRI) are due to particulate matter inhaled from indoor air pollution from household solid fuels (WHO, 2014).


    Nearly one quarter of all premature deaths due to stroke (i.e. about 1.4 million deaths of which half are in women) can be attributed to the chronic exposure to household air pollution caused by cooking with solid fuels.

    Ischaemic heart disease

    Approximately 15% of all deaths due to ischaemic heart disease, accounting for over a million premature deaths annually, can be attributed to exposure to household air pollution.

    Chronic obstructive pulmonary disease

    Over one-third of premature deaths from chronic obstructive pulmonary disease (COPD) in adults in low- and middle-income countries are due to exposure to household air pollution. Women exposed to high levels of indoor smoke are more than 2 times as likely to suffer from COPD than women who use cleaner fuels. Among men (who already have a heightened risk of COPD due to their higher rates of smoking), exposure to indoor smoke nearly doubles (i.e. 1.9) that risk.

    Lung cancer

    Approximately 17% of annual premature lung cancer deaths in adults are attributable to exposure to carcinogens from household air pollution caused by cooking with solid fuels like wood, charcoal or coal. The risk for women is higher, due to their role in food preparation.

    Other health impacts and risks

    More generally, small particulate matter and other pollutants in indoor smoke inflame the airways and lungs, impairing immune response and reducing the oxygen-carrying capacity of the blood.

    There is also evidence of links between household air pollution and low birth weight, tuberculosis, cataract, nasopharyngeal and laryngeal cancers.

    Mortality from ischaemic heart disease and stroke are also affected by risk factors such as high blood pressure, unhealthy diet, lack of physical activity and smoking. Some other risks for childhood pneumonia include suboptimal breastfeeding, underweight and second-hand smoke. For lung cancer and chronic obstructive pulmonary disease, active smoking and second-hand tobacco smoke are also main risk factors.

    Impacts on health equity, development and climate change

    Without a substantial change in policy, the total number of people relying on solid fuels will remain largely unchanged by 2030 (World Bank, 2010). The use of polluting fuels also poses a major burden on sustainable development.

    • Fuel gathering consumes considerable time for women and children, limiting other productive activities (e.g. income generation) and taking children away from school. In less secure environments, women and children are at risk of injury and violence during fuel gathering.
    • Black carbon (sooty particles) and methane emitted by inefficient stove combustion are powerful climate change pollutants.
    • The lack of access to electricity for at least 1.2 billion people (many of whom then use kerosene lamps for lighting) exposes households to very high levels of fine particulate matter, as well introduces other health risks, e.g. burns, injuries and poisonings from fuel ingestion, constraining other opportunities for health and development, e.g. studying or engaging in small crafts and trades, which require adequate lighting.
    WHO's response

    WHO provides technical support to countries in their own evaluations and scale-up of health-promoting household fuels and technologies. WHO is building capacity at the country and regional level to address household air pollution with workshops and the development of tools to help design, implement and monitor policies addressing household energy.


    New indoor air quality guidelines for household fuel combustion

    To ensure healthy air in and around the home, WHO’s new indoor air quality guidelines for household fuel combustion provide health-based recommendations on the types of fuels and technologies to protect health as well as strategies for the effective dissemination of such home energy technologies. These build upon existing WHO outdoor air quality guidelines and WHO guidance on levels of specific indoor pollutants.

    Household energy database

    The WHO Household Energy Database is used to monitor global progress in the transition to cleaner fuels and stove combinations, as well as contributes to assessments of disease burden from household energy and the energy access situation in low and middle-income countries. Recently this database has been expanded to include, in addition to extensive data on cooking, information on household fuels and technologies used for heating lighting and other impacts like time spent collecting fuel. The WHO Household Energy Database is used to monitor global progress in the transition to cleaner fuels and improved stoves as well as contribute to assessments of disease burden from household energy and the energy access situation in developing countries.

    Research and programme evaluation

    WHO is working with countries, researchers and other partners to harmonize methods of evaluation across settings so that health impacts are assessed consistently and rigorously and also incorporate economic assessment of health benefits.

    Leadership and advocacy in the health, energy and climate community
    Health sector

    WHO is working to integrate guidance and resources for supporting clean household energy into global health initiatives and decision-support tools, such as the Global Action Plan for Pneumonia and Diarrheal Disease (GAPPD), or Global Strategy for Women and Children’s Health, as well as into other aspects of WHO's own health policy guidance. WHO advocates about the compelling health arguments for cleaner household energy in a range of global forums addressing maternal and child health issues related to pneumonia as well as forums concerned with noncommunicable diseases in adults. This can help awareness of the importance of providing and scaling up of cleaner household energy as a core preventive public health measure.

    Health and climate change

    WHO is a partner of the Climate and Clean Air Coalition to Reduce Short-Lived Climate Pollutants (CCAC). As a member of the CCAC’s health task force, WHO is providing technical support for harnessing health benefits from actions to reduce short-lived climate pollutants, and working to scale up health sector engagement to address such pollutants and improve air quality.

    Health, energy and sustainable development

    Reductions in air pollution-related disease burden (both for household and outdoor) will be used to monitor the progress towards attaining the Sustainable Development Goal on Health (SDG 3).

    Ensuring universal access to clean fuel and technologies is a target of the Sustainable Development Goal on energy (SDG 7). If this target is met it could prevent millions of deaths and improve the health and well-being of the billions of people relying on polluting fuels and technologies for cooking, heating and lighting.

    To better assess the health risks, as well as differentiated gender impacts from household energy, WHO is leading an effort with countries and surveying agencies (e.g. USAID’s DHS, UNICEF’S MICS, World Bank’s LSMS) to enhance, harmonize and pilot new questions for national censuses. The effort will also survey to better capture information on all the fuels and technologies used in the home for cooking, heating and lighting, as well as other impacts like time lost to fuel collection.

    WHO also contributes to the development and updating of the global tracking framework used to measure progress toward the UN Secretary-General’s Sustainable Energy for All initiative target of universal access to clean energy by 2030.

    WHO also supports international initiatives to improve air pollution and related health impacts such as the Global Alliance for Clean Cookstoves and the Climate Clean Air Coalition.

    Ambient (outdoor) air quality and health


    Outdoor air pollution is a major environmental health problem affecting everyone in developed and developing countries alike.

    WHO estimates that in 2012, some 72% of outdoor air pollution-related premature deaths were due to ischaemic heart disease and strokes, while 14% of deaths were due to chronic obstructive pulmonary disease or acute lower respiratory infections, and 14% of deaths were due to lung cancer.

    Some deaths may be attributed to more than one risk factor at the same time. For example, both smoking and ambient air pollution affect lung cancer. Some lung cancer deaths could have been averted by improving ambient air quality, or by reducing tobacco smoking.

    A 2013 assessment by WHO’s International Agency for Research on Cancer (IARC) concluded that outdoor air pollution is carcinogenic to humans, with the particulate matter component of air pollution most closely associated with increased cancer incidence, especially cancer of the lung. An association also has been observed between outdoor air pollution and increase in cancer of the urinary tract/bladder.

    Ambient (outdoor air pollution) in both cities and rural areas was estimated to cause 3 million premature deaths worldwide per year in 2012; this mortality is due to exposure to small particulate matter of 10 microns or less in diameter (PM10), which cause cardiovascular and respiratory disease, and cancers.

    People living in low- and middle-income countries disproportionately experience the burden of outdoor air pollution with 87% (of the 3 million premature deaths) occurring in low- and middle-income countries, and the greatest burden in the WHO Western Pacific and South-East Asia regions. The latest burden estimates reflect the very significant role air pollution plays in cardiovascular illness and premature deaths – much more so than was previously understood by scientists.

    Most sources of outdoor air pollution are well beyond the control of individuals and demand action by cities, as well as national and international policymakers in sector like transport, energy waste management, buildings and agriculture.

    There are many examples of successful policies in transport, urban planning, power generation and industry that reduce air pollution:

    • for industry: clean technologies that reduce industrial smokestack emissions; improved management of urban and agricultural waste, including capture of methane gas emitted from waste sites as an alternative to incineration (for use as biogas);
    • for transport: shifting to clean modes of power generation; prioritizing rapid urban transit, walking and cycling networks in cities as well as rail interurban freight and passenger travel; shifting to cleaner heavy duty diesel vehicles and low-emissions vehicles and fuels, including fuels with reduced sulfur content;
    • for urban planning: improving the energy efficiency of buildings and making cities more compact, and thus energy efficient;
    • for power generation: increased use of low-emissions fuels and renewable combustion-free power sources (like solar, wind or hydropower); co-generation of heat and power; and distributed energy generation (e.g. mini-grids and rooftop solar power generation);
    • for municipal and agricultural waste management: strategies for waste reduction, waste separation, recycling and reuse or waste reprocessing; as well as improved methods of biological waste management such as anaerobic waste digestion to produce biogas, are feasible, low cost alternatives to the open incineration of solid waste. Where incineration is unavoidable, then combustion technologies with strict emission controls are critical.

    In addition to outdoor air pollution, indoor smoke is a serious health risk for some 3 billion people who cook and heat their homes with biomass fuels and coal. Some 4.3 million premature deaths were attributable to household air pollution in 2012. Almost all of that burden was in low-middle-income countries as well.

    The 2005 "WHO Air quality guidelines" offer global guidance on thresholds and limits for key air pollutants that pose health risks. The Guidelines indicate that by reducing particulate matter (PM10) pollution from 70 to 20 micrograms per cubic metre (μg/m), we can cut air pollution-related deaths by around 15%.

    The Guidelines apply worldwide and are based on expert evaluation of current scientific evidence for:

    • particulate matter (PM)
    • ozone (O3)
    • nitrogen dioxide (NO2) and
    • sulfur dioxide (SO2), in all WHO regions.

    Particulate matter

    Definition and principal sources

    PM affects more people than any other pollutant. The major components of PM are sulfate, nitrates, ammonia, sodium chloride, black carbon, mineral dust and water. It consists of a complex mixture of solid and liquid particles of organic and inorganic substances suspended in the air. The most health-damaging particles are those with a diameter of 10 microns or less, (≤ PM10), which can penetrate and lodge deep inside the lungs. Chronic exposure to particles contributes to the risk of developing cardiovascular and respiratory diseases, as well as of lung cancer.

    Air quality measurements are typically reported in terms of daily or annual mean concentrations of PM10 particles per cubic meter of air volume (m3). Routine air quality measurements typically describe such PM concentrations in terms of micrograms per cubic meter (μg/m3). When sufficiently sensitive measurement tools are available, concentrations of fine particles (PM2.5 or smaller), are also reported.

    Health effects

    There is a close, quantitative relationship between exposure to high concentrations of small particulates (PM10 and PM2.5) and increased mortality or morbidity, both daily and over time. Conversely, when concentrations of small and fine particulates are reduced, related mortality will also go down – presuming other factors remain the same. This allows policymakers to project the population health improvements that could be expected if particulate air pollution is reduced.

    Small particulate pollution have health impacts even at very low concentrations – indeed no threshold has been identified below which no damage to health is observed. Therefore, the WHO 2005 guideline limits aimed to achieve the lowest concentrations of PM possible.

    Guideline values

    10 μg/m3 annual mean
    25 μg/m3 24-hour mean

    20 μg/m3 annual mean
    50 μg/m3 24-hour mean

    In addition to guideline values, the Air Quality Guidelines provide interim targets for concentrations of PM10 and PM2.5 aimed at promoting a gradual shift from high to lower concentrations.

    If these interim targets were to be achieved, significant reductions in risks for acute and chronic health effects from air pollution can be expected. Progress towards the guideline values, however, should be the ultimate objective.

    The effects of PM on health occur at levels of exposure currently being experienced by many people both in urban and rural areas and in developed and developing countries – although exposures in many fast-developing cities today are often far higher than in developed cities of comparable size.

    "WHO Air Quality Guidelines" estimate that reducing annual average particulate matter (PM10) concentrations from levels of 70 μg/m3, common in many developing cities, to the WHO guideline level of 20 μg/m3, could reduce air pollution-related deaths by around 15%. However, even in the European Union, where PM concentrations in many cities do comply with Guideline levels, it is estimated that average life expectancy is 8.6 months lower than it would otherwise be, due to PM exposures from human sources.

    In developing countries, indoor exposure to pollutants from the household combustion of solid fuels on open fires or traditional stoves increases the risk of acute lower respiratory infections and associated mortality among young children; indoor air pollution from solid fuel use is also a major risk factor for cardiovascular disease, chronic obstructive pulmonary disease and lung cancer among adults.

    There are serious risks to health not only from exposure to PM, but also from exposure to ozone (O3), nitrogen dioxide (NO2) and sulfur dioxide (SO2). As with PM, concentrations are often highest largely in the urban areas of low- and middle-income countries. Ozone is a major factor in asthma morbidity and mortality, while nitrogen dioxide and sulfur dioxide also can play a role in asthma, bronchial symptoms, lung inflammation and reduced lung function.

    Ozone (O3)
    Guideline values

    100 μg/m3 8-hour mean

    The recommended limit in the 2005 Air Quality Guidelines was reduced from the previous level of 120 µg/m3 in previous editions of the "WHO Air Quality Guidelines" based on recent conclusive associations between daily mortality and lower ozone concentrations.

    Definition and principal sources

    Ozone at ground level – not to be confused with the ozone layer in the upper atmosphere – is one of the major constituents of photochemical smog. It is formed by the reaction with sunlight (photochemical reaction) of pollutants such as nitrogen oxides (NOx) from vehicle and industry emissions and volatile organic compounds (VOCs) emitted by vehicles, solvents and industry. As a result, the highest levels of ozone pollution occur during periods of sunny weather.

    Health effects

    Excessive ozone in the air can have a marked effect on human health. It can cause breathing problems, trigger asthma, reduce lung function and cause lung diseases. In Europe it is currently one of the air pollutants of most concern. Several European studies have reported that the daily mortality rises by 0.3% and that for heart diseases by 0.4%, per 10 µg/m3 increase in ozone exposure.

    Nitrogen dioxide (NO2)
    Guideline values

    40 μg/m3 annual mean
    200 μg/m3 1-hour mean

    The current WHO guideline value of 40 µg/m3 (annual mean) was set to protect the public from the health effects of gaseous.

    Definition and principal sources

    As an air pollutant, NO2 has several correlated activities.

    • At short-term concentrations exceeding 200 μg/m3, it is a toxic gas which causes significant inflammation of the airways.
    • NO2 is the main source of nitrate aerosols, which form an important fraction of PM2.5 and, in the presence of ultraviolet light, of ozone.

    The major sources of anthropogenic emissions of NO2 are combustion processes (heating, power generation, and engines in vehicles and ships).

    Health effects

    Epidemiological studies have shown that symptoms of bronchitis in asthmatic children increase in association with long-term exposure to NO2. Reduced lung function growth is also linked to NO2 at concentrations currently measured (or observed) in cities of Europe and North America.

    Sulfur dioxide (SO2)
    Guideline values

    20 μg/m3 24-hour mean
    500 μg/m3 10-minute mean

    A SO2 concentration of 500 µg/m3 should not be exceeded over average periods of 10 minutes duration. Studies indicate that a proportion of people with asthma experience changes in pulmonary function and respiratory symptoms after periods of exposure to SO2 as short as 10 minutes.

    The (2005) revision of the 24-hour guideline for SO2 concentrations from 125 to 20 μg/m3 was based on the following considerations.

    • Health effects are now known to be associated with much lower levels of SO2than previously believed.
    • A greater degree of protection is needed.
    • Although the causality of the effects of low concentrations of SO2 is still uncertain, reducing SO2 concentrations is likely to decrease exposure to co-pollutants.
    Definition and principal sources

    SO2 is a colourless gas with a sharp odour. It is produced from the burning of fossil fuels (coal and oil) and the smelting of mineral ores that contain sulfur. The main anthropogenic source of SO2 is the burning of sulfur-containing fossil fuels for domestic heating, power generation and motor vehicles.

    Health effects

    SO2 can affect the respiratory system and the functions of the lungs, and causes irritation of the eyes. Inflammation of the respiratory tract causes coughing, mucus secretion, aggravation of asthma and chronic bronchitis and makes people more prone to infections of the respiratory tract. Hospital admissions for cardiac disease and mortality increase on days with higher SO2 levels. When SO2 combines with water, it forms sulfuric acid; this is the main component of acid rain which is a cause of deforestation.

    WHO response (Ambient)
    • WHO Member States recently adopted a resolution and a road map for an enhanced global response to the adverse health effects of air pollution.
    • WHO develops and produces "Air quality guidelines" recommending exposure limits to key air pollutants.
    • WHO creates detailed health-related assessments of different types of air pollutants, including particulates and black carbon particles, ozone, etc.
    • WHO produces evidence regarding the linkage of air pollution to specific diseases, such as cardiovascular and respiratory diseases and cancers, as well as burden of disease estimates from existing air pollution exposures, at country, regional, and global levels.
    • WHO’s "Health in the green economy" series is assessing the health co-benefits of climate mitigation and energy efficient measures that reduce air pollution from housing, transport, and other key economic sectors.
    • WHO’s work on "Measuring health gains from sustainable development" has proposed air pollution indicators as a marker of progress for development goals related to sustainable development in cities and the energy sector.
    • WHO assists Member States in sharing information on successful approaches, on methods of exposure assessment and monitoring of health impacts of pollution.
    • The WHO co-sponsored "Pan European Programme on Transport Health and Environment (The PEP)", has built a model of regional, Member State and multi-sectoral cooperation for mitigation of air pollution and other health impacts in the transport sector, as well as tools for assessing the health benefits of such mitigation measures.


    Air Pollution