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Air pollution is the presence of substances in the air that are harmful to humans, other living beings or the environment. Pollutants can be Gas like ozone or nitrogen oxides or small particles like soot and dust. It affects both outdoor air and indoor air.
Natural sources of air pollution include Wildfire, Dust storm, and volcanic eruptions. Indoor air pollution is often caused by the use of biomass (e.g. wood) for cooking and heating. Outdoor air pollution comes from some industrial processes, the burning of Fossil fuel for electricity and transport, waste management and agriculture. Many of the contributors of local air pollution are also sources of greenhouse emissions i.e., burning of fossil fuel.
Air pollution causes around 7 or 8 million deaths each year. It is a significant risk factor for a number of diseases, including stroke, heart disease, chronic obstructive pulmonary disease (COPD), asthma and lung cancer. Particulate matter is the most deadly, both for indoor and outdoor air pollution. Ozone affects crops, and forests are impacted by the pollution that causes acid rain. Overall, the World Bank has estimated that welfare losses (premature deaths) and productivity losses (lost labour) caused by air pollution cost the world economy over $8 trillion per year.
Many different technologies and strategies are available for reducing air pollution. National air quality laws have often been highly effective, notably the 1956 Clean Air Act in Britain and the US Clean Air Act, introduced in 1963. Some of these efforts have been successful at the international level, such as the Montreal Protocol, which reduced the release of harmful Ozone layer-depleting chemicals, while others, such as international action on climate change, have been less successful.
Other industries cause air pollution too. A 2014 study found that in China, manufacturing and construction sectors contributed more than 50% of air pollution. This was due to high emission intensity and high emission factors in its industrial structure. Polluting industries have been pushed out of richer nations, and China has also started to push its most polluting industries out of the country.
Construction, renovation and demolition produces dust, but also other pollutants. Though banned in many countries, asbestos persists in older buildings, where it poses a risk of lung disease when disturbed. Building materials including carpeting and plywood emit formaldehyde (H-CHO) gas.
Open dump of waste are a common source of air pollution in low-income countries. They can support the growth of microbes which pollute water and air, and be a source of toxins. Through open burning of waste—whether self-ignited or burned on purpose—soot, methane, and other pollutants are released. The waste in landfills itself also produces methane. Globally, a quarter of solid waste is not collected. Another quarter is not disposed of properly.
Gas stove for cooking contribute to indoor air pollution by emitting , benzene and carbon monoxide. Toaster can produce particulate pollution. Similarly, Heating system such as furnaces and other types of fuel-burning heating devices release polllutants into the air. In some developed countries, including the UK and Sydney, Australia, wood stoves are the major source of particulate pollution in urban areas. Wood stoves can also emit carbon monoxide and .
Other sources of indoor air pollution are radon, building materials, biological material and tobacco smoke. Biological material, such as dander, house dust mite, mold and pollen, can come from humans, animals or plants. Some of this material can trigger allergies, such as allergic rhinitis. Fumes from paint, hair spray, varnish, can be substantial; emissions from these sources was estimated to account for almost half of pollution from volatile organic compounds in the Los Angeles basin in the 2010s.
Radon is a radioactive gas that can build up in buildings from the soil. It can cause lung cancer, especially in Smoking. Levels are generally low, but can be elevated in buildings with "leaky" foundations or areas with soils rich in uranium. (2025). 9781788016179, Royal Society of Chemistry. ISBN 9781788016179
Vegetation, in some regions, emits environmentally significant amounts of volatile organic compounds (VOCs) on warmer days. These VOCs react with human pollution sources – specifically, NOx, SO2, and organic carbon – to produce a seasonal haze of secondary pollutants. Black gum, poplar, oak and willow are some examples of vegetation that can produce abundant VOCs. The VOC production from these species result in ozone levels up to eight times higher than the low-impact tree species.
Volcano eruptions produce mostly steam (about 79 percent), but also carbon dioxide (12 per cent), sulfur dioxide (6.5 percent), and small amounts of other pollutants, such as chlorine and ash particulates.
is sometimes called an air pollutant, because it is the main [[greenhouse gas]] responsible for [[climate change]]. This question of terminology has practical consequences, for example, in determining whether the U.S. Clean Air Act (which is designed to improve air quality) is deemed to regulate emissions. The Inflation Reduction Act of 2022 amended the Clean Air Act to define from fossil fuel burning explicitly as an air pollutant.
Sea spray, wildfires, volcanoes and Dust storm are the main natural sources of PM, while the burning of biomass and fossil fuels, as well as road emissions and dust resuspension are the main human sources. Human PM is usually finer than natural PM. A definitive link between fine particulate pollution and higher death rates in urban areas was established by the Harvard Six Cities study, published in 1993.
High concentrations of SO2 in the air generally also lead to the formation of other sulfur oxides (SOx). SOx can react with other compounds in the atmosphere to form small particles and contribute to particulate matter pollution. At high concentrations, gaseous SOx can harm plants by damaging Leaf and decreasing growth. Further oxidation of SO2, mostly taking place in cloud droplets, forms sulfuric acid (H2SO4), which is one of the components of acid rain.
Persistent organic pollutants (POPs) are organic compounds that are resistant to environmental degradation. As a result, they persist in the environment, are capable of long-range transmission, bioaccumulate in humans and animals and Biomagnification in food chains. The Stockholm Convention on Persistent Organic Pollutants identified Pesticide and other POPs of concern. These include dioxins and furans which are created by waste combustion. POPs are usually either semi-volatile (gaseous only at higher temperatures) or non-volatile (emitted as particles). The harmful effects of the pesticide DDT, a POP, was popularised Silent Spring in the 1960. PFASs and polycyclic aromatic hydrocarbons (PAHs) are other examples of POPs.
Chlorofluorocarbons (CFCs) are a group of compounds which harm the ozone layer. These gases were emitted by air conditioners, freezers, aerosol sprays, and other similar devices. CFCs reach the stratosphere after being released into the atmosphere. They interact with other gases here, causing harm to the ozone layer. UV rays are able to reach the Earth's surface as a result of this. This can result in skin cancer, eye problems, and even plant damage.
some pollutants, low exposure can be seen as safe, whereas other pollutants have negative health effects even at low levels. As evidence has grown that even very low levels of air pollutants hurt human health, the WHO halved its recommended safe limit for particulate matter from 10 μg/m3 to 5 μg/m3 in 2021. Under the new guideline, nearly the entire global population—97.3 percent—is classified as exposed to unsafe levels of PM2.5. The new limit for nitrogen dioxide (NO2) became 75% lower. For all pollutants together, the WHO concluded that 99% of the world population is exposed to harmful air pollution.
For some pollutants such as black carbon, traffic related exposures may dominate total exposure despite short exposure times since high concentrations coincide with proximity to major roads or participation in (motorized) traffic. A large portion of total daily exposure occurs as short peaks of high concentrations.
Studies show that patterns in race and income disparities not only indicate a higher exposure to pollution but also higher risk of adverse health outcomes. Communities characterized by low socioeconomic status and racial minorities can be more vulnerable to cumulative adverse health impacts resulting from elevated exposure to pollutants than more privileged communities. In the United States, Blacks and Latinos generally face more pollution than Whites and Asians, and low-income communities bear a higher burden of risk than richer ones. Residents in public housing, who are generally low-income and cannot move to healthier neighborhoods, are highly affected by nearby Refinery and chemical plants.
| +Top 5 most polluted cities in 2024 !City !PM2.5 concentration | |
| Byrnihat | 128 |
| Delhi, India | 108 |
| Karaganda, Kazakhstan | 105 |
| Mullanpur Dakha, India | 102 |
| Lahore, Pakistan | 102 |
Pollutants strongly linked to negative health effects include particulate matter, carbon monoxide, nitrogen dioxide (NO2), ozone (O3), and sulphur dioxide (SO2). Fine particulates are especially damaging, as they can enter the bloodstream via the lungs and reach other organs. Air pollution causes disease by driving inflammation and oxidative stress, suppressing the immune system and by damaging DNA.
Even at very low levels (under the World Health Organization recommended levels), fine particulates can continue to cause harm. However, according to the WHO, 99% of the world's population lives in areas with air pollution that exceeds WHO recommended levels. People living in poverty, babies and Old age are also disproportionately affected by air pollution; pregnancy is also more risky when exposed to air pollution.
The WHO estimates that 6.7 million people die from air pollution each year, 4.2 million due to outdoor air pollution. Roughly 68% of outdoor air pollution-related premature deaths were due to ischaemic heart disease and stroke, 14% due to COPD and 14% due to lung infections (lower respiratory tract infections).
A study published in 2019 estimated that, for 2015, the number was around 8.8 million, with 5.5 million of these premature deaths due to air pollution from human sources. The global mean loss of life expectancy from air pollution in 2015 was 2.9 years, substantially more than, for example, 0.3 years from all forms of direct violence.
Annual premature European deaths from air pollution are estimated at 416,000 to 800,000. The UK saw some 17,000 deaths in 2021 due to air pollution. Nigeria, Indonesia and Pakistan each saw over 200,000 deaths resulting from air pollution.
Eliminating energy-related emissions in the United States would prevent 46,900–59,400 premature deaths each year and provide $537–$678 billion in benefits from avoided PM2.5-related illness and death. A 2023 study on sulfur dioxide emissions by coal power plants (coal PM2.5) concluded that "exposure to coal PM2.5 was associated with 2.1 times greater mortality risk than exposure to PM2.5 from all sources." From 1999 to 2020, a total of 460,000 deaths in the US were attributed to coal PM2.5.
A study concluded that PM2.5 air pollution induced by the contemporary free trade and consumption by the G20 nations causes two million premature deaths annually, suggesting that the average lifetime consumption of about ~28 people in these countries causes at least one premature death (average age ~67) while developing countries "cannot be expected" to implement or be able to implement countermeasures without external support or internationally coordinated efforts.
The World Health Organization (WHO) estimates that cooking-related pollution causes 3.8 million annual deaths. The Global Burden of Disease study estimated the number of deaths in 2021 at 3.1 million.
Air pollution is a leading risk factor for stroke, particularly in developing countries where pollutant levels are highest. A systematic analysis of 17 different risk factors in 188 countries found air pollution is associated with nearly one in three strokes (29%) worldwide (34% of strokes in developing countries versus 10% in developed countries). The mechanisms linking air pollution to increased cardiovascular mortality are not fully understood, but likely systemic inflammation and oxidative stress.
Air pollution is further associated with increased risk of asthma and worsening of symptoms, and this effect seems stronger in children. For adults, fine particles (PM2.5) or NO2 seem linked to asthma onset too. Short-term exposure to ozone makes asthma worse in children. There is limited evidence on (almost) fatal asthma attacks in children: ground-level ozone and PM2.5 seem to increase its risk.
The risk of lung disease from air pollution is greatest for infants and young children, whose normal breathing is faster than that of older children and adults; the elderly; those who work outside or spend a lot of time outside; and those who have heart or lung disease Comorbidity.
Outdoor air pollution may increase risk of other types of cancer too, but the evidence is not as clear as for lung cancer. For instance, there may be a relationship between kidney cancer and PM2.5 and NO2 levels. Household air pollution, for instance from cooking with solid fuels, but also from radon in building material, has been associated with Cervical cancer, Oral sex, and esophageal cancer.
Over a third of preterm births were associated with air pollution in 2021 globally. It causes more than half a million newborn deaths, a quarter of overall deaths. The source of PM2.5 differs greatly by region. In South and East Asia, pregnant women are frequently exposed to indoor air pollution because of wood and other biomass fuels being used for cooking, which are responsible for more than 80% of regional pollution. In the Middle East, North Africa and West sub-Saharan Africa, fine PM comes from natural sources, such as .
Including older children, polluted air leads resulted in the death of over 700,000 children in 2021 (709,000 under 5 years of age and 16,600 aged 5–14 years). Children in low or middle income countries are exposed to higher levels of fine particulate matter than those in high income countries. Further health effects of air pollution on children include asthma, pneumonia and lower respiratory tract infections. There is possibly a link between exposure to air pollution during pregnancy and after birth and autism in children.
Exposure to air pollution may also drive mental health issues, such as depression and Anxiety disorder. In particular, air pollution from the use of solid fuels was associated with a higher depression risk. Depression risk and suicide was more strongly linked to finer particulate matter (PM2.5), compared to coarser particles (PM10). The association was strongest for people over the age of 65.
Problems with thinking (cognitive issues) are also associated with air pollution. In people over the age of 40, both NOx and PM2.5 have been linked to general cognitive problems. PM2.5 was also associated with reduced verbal fluency (for instance, number of animals one can list in a minute) and worse executive functions (like attention and working memory). Similarly, children tended to fare worse in tests involving working memory when there was NOx, PM2.5, or PM10 pollution.
The COVID-19 lockdowns served as a natural experiment to expose the close links between air quality and surface greenness. In India, the lockdown induced improvement in air quality, enhanced surface greenness and photosynthetic activity, with the positive response of vegetation to reduce air pollution was dominant in croplands. On the other hand, agriculture in its traditional form is one of the primary contributors to the emission of trace gases like atmospheric ammonia.
In terms the welfare cost on human health (non-market costs), a World Bank study found that PM2.5 pollution in 2019 cost the world economy over $8 trillion, over 6% of global GDP. In India and China, the loss of GDP was over 10%. Around 85% of this loss globally came from the loss of life, the rest from increased ill health. The costs of lives lost are calculated using the Value of Statistical Life, a number that tries to estimate how much people would be willing to pay to reduce their risk of dying. This number differs by country and is difficult to estimate for low- and middle-income countries.
The direct market impacts on productivity loss, healthcare use and crop losses were estimated to rise to 1% of GDP by 2060, according to the OECD. The Caspian region and China would see the largest impact. Air pollution also has an impact on energy production, as it reduces the amount of sunlight that reaches Solar panel. It also causes the panels to become dirty, further reducing their energy output.
During the Industrial Revolution, outdoor air pollution started to rise strongly, mostly due to the large-scale burning of coal. This occurred first in Britain, then in the rest of Northern Europe and the United States. By the 19th century, buildings around industrial plants started to blacken, while plants and trees in public parks started to wither. Smoke-induced fogs reduced the amount of sunlight city-dwellers got, contributing to cases of rickets, a childhood disease caused by lack of sunlight and poor diet. In the 1830s, anti-smoke groups emerged in Britain, followed by groups in the United States in the 1880s. Legislation against pollution was weak however, as it was seen to conflict with industrial interests. During the Interwar period, a move towards gas and oil meant there was less air pollution, but this trend reversed when World War II broke out. The United Kingdom suffered its worst air pollution during the 1952 Great Smog of London, with some 12,000 deaths, which led to the Clean Air Act 1956. The 1948 Donora Smog in the US, killing 20 people, prompted the US to start regulating air pollution. Japan followed in the 1960, but other heavily-polluted regions, such as the Soviet Union and China, did not implement effective regulation.
Technological disasters have caused severe problems with air pollution. The world's worst pollution disaster was the 1984 Bhopal Disaster in India. Leaked industrial vapours from the Union Carbide factory (later bought by Dow Chemical Company), killed at least 20,000 people and affected around 600,000. An accidental leak of anthrax spores from a biological warfare laboratory in the former USSR in 1979 is believed to have caused at least 64 deaths.
From the 1950s, smog in developed countries was regulated, but other pollutants were not. Acid rain, caused by Sulfur dioxide, became a major issue as it spread across borders. In the 1990s, for instance, Japan experienced acid rain from Chinese and Korean industry. International cooperation was needed to curb acid rain, and various coalitions were started. In 1975, it was discovered that certain chemicals caused a hole in the ozone layer; thanks to succesfull international negotiations, these chemicals were banned worldwide in the 1987 Montreal Protocol. There has been far less success in curbing greenhouse gas emissions, mostly from the production and burning of fossil fuels. The 1997 Kyoto Protocol introduced modest reduction targets but lacked strong enforcement, while the 2015 Paris Agreement set no binding limits, instead encouraging countries to raise their ambition over time.
Air quality indexes (AQIs) offer a simple way for governments to communicate changes in air quality and associated health risks, especially during short-term pollution episodes, such as wildfires. An AQI is essentially a health protection tool people can use to help reduce their short-term exposure to air pollution by adjusting activity levels during increased levels of air pollution. Examples include Canada's Air Quality Health Index (AQHI), Malaysia's Air Pollution Index, and Singapore's Pollutant Standards Index.
Air quality models use Meteorology and emissions data to simulate how pollutants disperse and react in the atmosphere. Regulatory agencies use them to assess whether a new source of air pollution would exceed acceptable pollution levels, for permitting purposes. They can also be used to predict future pollution levels under different policy scenarios. There are models for local pollution, but also for cross-boundary pollution.
In the power sector, a very effective means to reduce air pollution is the transition to renewable energy or nuclear power.
A growing number of countries regulates waste, which include national or city-wide waste management systems, opening managed Landfill, landfill gas capture (for electricity production), and Waste sorting. In agriculture, air pollution can be minimised by not overusing fertilisers and by not feeding excess protein to livestock.
Traffic can be shifted to cleaner modes of transport, for instance by increased use of public transport. The 9-Euro-Ticket scheme in Germany which allowed people to buy a monthly pass allowing use on all local and regional transport (trains, trams and busses) for 9 euro (€) for one month of unlimited travel saved 1.8 million tons of emissions during its three-month implementation from June to August 2022. Finally, road vehicles can be improved from increased fuel efficiency, conversion to cleaner fuels, and conversion to . For example, buses in New Delhi, India, have run on compressed natural gas since 2000, to help eliminate the city's "pea-soup" smog. Phase-out of fossil fuel vehicles is a critical component of a shift to sustainable transport. However, even in electric vehicles, Rubber pollution, ranking as 13th worst pollutant in Los Angeles.
Areas downwind (over 20 miles) of major airports have more than double total particulate emissions in air than other areas, even when factoring in areas with frequent ship calls, and heavy freeway and city traffic like Los Angeles. Aviation biofuel mixed in with jetfuel at a 50/50 ratio can reduce jet derived cruise altitude particulate emissions by 50–70%, according to a NASA led 2017 study (however, this should imply ground level benefits to urban air pollution as well).
Kerosine for lighting can be replaced with efficient , for instance solar-powered LED lights. Combustion of fossil fuels for space heating can be replaced by using heat pumps and seasonal thermal energy storage.
In the United Kingdom, air pollution campaigning currently involves a mixture of grassroots activism (by groups such as Mums for Lungs and individual campaigners such as Rosamund Kissi-Debrah), public health awareness (through events such as Clean Air Day), legal work (advanced by activist lawyers such as ClientEarth), and more traditional campaigning (by environmental groups such as Greenpeace and Friends of the Earth, public health advocacy groups such as British Lung Foundation and Asthma UK, and organizations that raise health and safety issues, such as the British Safety Council). Citizen science projects combine scientific research with public health awareness raising and grassroots environmental campaigning.
In 2019, the Court of Justice of the EU, found that France did not comply with the limit values of the EU air quality standards applicable to the concentrations of nitrogen dioxide (NO2) in 12 air quality zones.
Some air pollution laws include specific air quality standards, such as the U.S. National Ambient Air Quality Standards and E.U. Air Quality Directive, which specify maximum atmospheric concentrations for specific pollutants. Other examples of air quality laws around the world include the Clean Air Act in Britain, the US Clean Air Act, and TA Luft in Germany. Some air pollution laws put limits on emissions (e.g. from vehicles), as well as air standards.
The World Health Organization's Global Air Quality Guidelines encourage improvements in a similar way to national standards, but are "recommendations" and "good practice" rather than mandatory targets that countries must achieve.
Other networks include the C40 Cities Climate Leadership Group, a public 'non-state' network of the world's leading cities that aims to curb their greenhouse emissions. The C40 has been identified as 'governance from the middle' and is an alternative to intergovernmental policy. It has the potential to improve urban air quality as participating cities "exchange information, learn from best practices and consequently mitigate carbon dioxide emissions independently from national government decisions". A criticism of the C40 network is that its exclusive nature limits influence to participating cities and risks drawing resources away from less powerful city and regional actors.
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