Frequently Asked Questions on Air Pollution

All the questions you've ever had on this deadly form of pollution, answered by scientists from all over the world.

1. WHY IS IT SO IMPORTANT TO REDUCE AIR POLLUTION?

Air pollution is all around us. Most people in the world live in areas with high levels of air pollution. It harms human health and wellbeing, reduces quality of life, and can negatively impact the economy and ecosystems. These impacts also disproportionately affect the most vulnerable people and communities.

Air pollution is the largest environmental risk to public health globally. People everywhere are exposed to air pollution: in the workplace, during travel, and in their homes. Exposure to household and ambient (outdoor) fine particulate matter air pollution causes an estimated 6.7 million premature deaths each year, according to the World Health Organization (WHO), and is responsible for a substantial amount of disability for those living with diseases caused by air pollution.

While complex and requiring a coordinated government response, air pollution can be greatly reduced. Air pollution is also a transboundary issue, meaning that pollution does not stop at administrative or country borders, which means countries and communities must cooperate to address the problem.

In many developing countries, reliance on solid fuels (like biomass and coal for cooking and heating, and the use of kerosene for lighting) increases air pollution in homes, harming the health of those exposed. WHO estimates that more than 2.3 billion people rely on these types of fuels. Most of these effects are felt in parts of Asia and sub-Saharan Africa, where burning biomass for cooking is especially prevalent.

While the impacts on human health are the most pressing, air pollution also significantly impacts several different types of ecosystems. For example, it could cause the extinction of ozone-sensitive plant species. It reduces crop yields as well as the yield and health of forests. It also reduces atmospheric visibility and increases corrosion of materials, buildings, monuments, and cultural heritage sites, and causes acidification of sensitive lake ecosystems.

Air pollution also has high economic costs related to human health, lost productivity, reduced crop yields and reduced competitiveness of globally connected cities. For example, a 2021 World Bank study found that the economic cost of only the health impacts of air pollution totalled US$8.1 trillion, equivalent to 6.1 percent of global Gross Domestic Product (GDP) in 2019.

Air pollution is strongly linked to climate change, with many greenhouse gases (GHGs) and air pollutants coming from the same sources. Many air pollutants are both bad for human health and deadly for the planet, impacting people’s lives today and making the future less safe for coming generations. This has given rise to coordinated measures to reduce air pollution and GHGs, such as those addressing Short-Lived Climate Pollutants (SLCPs). Higher temperatures can also increase the volatilization of some pollutants, such as Persistent Organic Pollutants (POPs) that are already in the environment, causing addition exposure to these pollutants.

Reducing air pollution is tied to the achievement of the Sustainable Development Goals (SDGs), and directly affects the achievement of SDG 2: Zero Hunger, SDG 3: Good Health and Wellbeing, SDG 7: Affordable and Clean Energy, SDG 11: Sustainable Cities and Communities, and SDG 13: Climate Change. It indirectly impacts the achievement of many other SDGs: SDG 3: Good Health and Wellbeing, SDG 7: Affordable and Clean Energy, SDG 11: Sustainable Cities and Communities, and SDG 13: Climate Change. It indirectly impacts the achievement of many other SDGs.

From past and current experience, we know that much of human caused air pollution is preventable, and as the examples show, reducing air pollution will provide additional benefits like healthier and more productive lives, a healthier natural environment, poverty alleviation and increased shared prosperity.

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2. WHAT IS AIR POLLUTION?

Air pollution is caused by gases and particles emitted to the atmosphere from a variety of human activities, such as the inefficient combustion of fuels or the open burning of waste, agriculture, and farming. There are also natural sources contributing to air pollution, many of which are impacted by human activities such as forest fires, soil dust, and salt in sea spray.

Air pollutants can be emitted directly from a source (i.e. primary pollutants) or can form from chemical reactions in the atmosphere (i.e. secondary pollutants). When concentrations of these substances reach critical levels in the air, they harm humans, animals, plants and ecosystems, reduce visibility and corrode materials, buildings and cultural heritage sites.

The main pollutants affecting human health are particulate matter, ground-level ozone (O₃) and nitrogen dioxide (NO₂), sulfur dioxide (SO₂), ammonia (NH₃), volatile organic compounds (VOCs), and carbon monoxide (CO). The fine particles that damage human health are known as PM_2.5 (particles with a diameter of less than 2.5 micrometres), which can penetrate deep into the lungs and pass into the bloodstream affecting different organs and bodily functions. These particles can either be emitted directly (e.g. black carbon, organic carbon, mineral particles, brake dust and tire wear) or formed in the atmosphere from several different emitted pollutants (e.g. SO₂, NO_X, NH₃, and VOCs).

Ozone (O₃) is an important secondary pollutant. It is a potent lung irritant and stunts growth in plants, including important crops and trees. It is also a powerful greenhouse gas (GHG). O₃ is formed in the troposphere, near the Earth’s surface, when certain precursor pollutants (NOx, non-methane VOCs, methane, CO) react in the presence of sunlight. The powerful GHG methane (CH₄), is responsible for a significant portion of O₃ formation. This tropospheric ozone is different from the ozone in the upper atmosphere (stratosphere), which protects us from ultraviolet light from the sun.

Nitrogen oxides (NOx) are a group of air polluting chemical compounds, comprising nitrogen dioxide (NO₂) and nitrogen monoxide (NO). NO₂ is the most harmful of these compounds for human health and is generated from human activities. It impacts human health, reduces atmospheric visibility, and can play a significant role in climate change, at high concentrations. Finally, it is a critical precursor to the formation of O₃ and fine particulate.

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3. HOW LONG HAS AIR POLLUTION BEEN A PROBLEM?

Air pollution has been associated with humans for millennia, starting with the use of fire for cooking and warmth. Dangerously high levels of outdoor air pollution became a problem during the industrial revolution, where the massive use of coal gave rise to many episodes of serious urban air pollution.

The case of the London Smog Disaster of 1952, is an extreme example, causing a surge in deaths over a one-week episode. The pollution from residential coal fires, coal for electricity generation, dirty transport fuels, and industrial pollution interacted with weather phenomena which trapped the pollution over London and led to over 4,000 excess deaths over just a few days and estimates of up to 12,000 in the following few weeks. The public outcry that followed led to the adoption of the UK Clean Air Act (1956). Other fatal air pollution episodes, like in Donora, USA (1948), and Meuse Valley, Belgium (1930), prompted similar actions to be taken to tackle air pollution in other countries.

Continued reliance on fossil fuels through the 20th century saw air pollution increase as countries industrialized. In newly industrialised countries like China and India, this has led to extreme air pollution events, like those experienced in the past in the USA and Europe. However, new forms of cleaner and renewable energy, and the adoption of air quality regulations and management processes, are reducing reliance on some polluting fuels and practices.

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4. WHERE DOES AIR POLLUTION COME FROM?

Air pollution comes from a wide array of sources, both natural and caused by human activities (anthropogenic). Natural sources include volcanic eruptions, sea spray, soil and desert dust, natural vegetation fires and lightning. Some of the most common human activity-related sources include power generation, transportation, industry, residential heating and cooking, agriculture, solvent use, oil and gas production, waste burning and construction. Some sources, such as forest and savanna fires and windblown mineral dust, occur naturally, but are exacerbated by human activities.

For much of the world’s population, human activities account for most of the air pollution they are exposed to.

Different pollutants have different sources. In cities, air pollution comes from both inside and outside city boundaries, some of it travelling over long distances. Major urban sources include vehicles, burning of gas, coal and charcoal, wood for cooking and heating, and industrial sources located in cities. Many large industrial sources, such as cement plants, steel plants and electricity generation, oil and gas production and refining, and maritime sources are often located away from cities, but still contribute a lot to the urban air pollution through long distance transport in the air.

Agricultural sources, including burning to clear land, and forest fires, contribute a lot to urban and rural air pollution levels. Most ammonia is emitted from agriculture and human waste treatment and can lead to PM_2.5 formation. In very dry areas, close to deserts and eroded land, wind-blown dust can make up a large fraction of the PM_2.5.

One of the most common sources of air pollution in rural and peri-urban areas of low- and middle-income countries comes from households burning biomass, other solid fuels like coal, or kerosene for cooking, heating and lighting. Household air pollution also contributes to outdoor air pollution.

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5. IS AIR POLLUTION MAINLY A LOCAL PROBLEM OR CAN IT TRAVEL LONG DISTANCES?

Air pollution significantly impacts places near its source, but because it can be carried long distances in the atmosphere, air pollution can also affect faraway places. For example, pollutants that form into fine particulate matter (PM_2.5), persistent organic pollutants (POPs), and ozone (O₃) can travel over hundreds or thousands of kilometres, causing regional and continental impacts. This transboundary air pollution leads to challenges for regulations and enforcement because different countries or regions, have little regulatory control over air pollution coming from outside their borders (also see question 14).

Despite the contribution of long-distance air pollutants to local air pollution, nearby sources remain a very significant determining factor of local air quality. Pollutants like nitrogen dioxide (NO₂) and sulphur dioxide (SO₂)_, have concentration levels which are highest close to their sources (transport, energy production and industries). Within a city, areas closest to large sources can have huge pollutant concentrations, while other areas of the same city can be much cleaner.

Atmospheric conditions, such as wind, affect pollutant dispersion and can vary widely. Strong winds enable long-distance transport, and stagnant conditions can lead to a build-up of pollutants. Large cities in subtropical and tropical regions that have very light winds and many hours of sunshine experience serious pollution episodes. Mountains surrounding cities, land-sea breezes, and other local weather conditions can affect the spread of pollutants and influence the formation of secondary pollutants.

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6. HOW DOES AIR POLLUTION AFFECT HUMAN HEALTH?

The air pollutant of greatest concern for human health, and which we know most about, is fine particulate matter. This has a diameter of 2.5 micrometres or less, which is why it is also known as PM_2.5. These fine particles are invisible to the human eye and 40 times smaller than the width of a human hair. They can do a lot of damage to our bodies: these particles are small enough to penetrate deep into our lungs, where they cause inflammation of sensitive lung tissue and can pass into the blood stream, affecting organs like the heart and brain. The WHO estimates that, globally, air pollution is responsible for about 6.7 million premature deaths per year.

Air pollution causes both acute disease and chronic disease. There is strong evidence linking long-term exposure (i.e. exposure over many months or years) to air pollution with an increased risk for ischaemic heart disease, stroke, chronic obstructive pulmonary disease (COPD), lung and upper aerodigestive cancers, adverse pregnancy outcomes (i.e. low-birth rate, pre-term births and reduced birth weight (babies born weighing less than five pounds / 2.2 kilos), diabetes and cataracts. The WHO’s International Agency for Research on Cancer (IARC) has designated outdoor air pollution as a carcinogen.

Some immediate health effects of air pollution exposure, even for a few minutes to a few hours, include irritation of the eyes, nose and throat, shortness of breath, cough, and exacerbation of pre-existing conditions, like asthma attacks and chest pain. Age, pre-existing conditions, and other risk factors for disease and sensitivity to the pollutant can all affect how a person reacts to air pollution.

Air pollutant gases can also seriously affect human health. Carbon monoxide (CO) restricts the transfer of oxygen to tissues and can be fatal in very high concentrations. Sulphur dioxide (SO₂) is a potent lung irritant affecting the health of those with pre-existing respiratory disease (asthma and COPD), especially those living and working close to SO₂ sources. Nitrogen oxides (NOx) are linked to a range of impacts, spanning from respiratory irritation to the development of asthma and increased mortality. Exposure to ozone (O₃) causes respiratory diseases and was associated with 365,000 premature deaths in 2019, according to the Global Burden of Disease (IHME).

Left out of these statistics are the serious health consequences that have been associated with air pollution in the scientific literature, but for which data and/or methods do not yet exist in order to estimate attributable disease burdens on a global scale, or for which more research is needed to establish causal attribution in a rigorous and statistically robust way. For example, studies have identified associations between air pollution and asthma, cognitive decline and dementia in later life, and pregnancy loss and infant mortality. As the research continues to develop, and more of these health outcomes are incorporated into the GBD estimates, the air pollution- related disease burden is likely to change over time.

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7. HOW DOES AIR POLLUTION AFFECT CHILDREN'S HEALTH?

Children are particularly vulnerable to the damaging health effects of air pollution due to their unique susceptibility and exposure. Children’s respiratory tracts are more permeable, their breathing rate is twice as much as adults, and they take in more air per kilogram (kg) of their body weight. Children’s bodies, especially their lungs and brains, are still developing, with narrower blood vessels. And their immune systems are weaker than adults; hence, polluted air affects children more than adults.

According to State of Global Air 2020 estimates, air pollution contributed to nearly 500,000 deaths among infants in their first month of life in 2019. Most of those deaths related to complications of low birth weight and preterm birth. According to the World Health Organization close to half of deaths due to pneumonia among children under 5 years of are caused by particulate matter inhaled from household air pollution. 20 percent of newborn deaths are attributed to air pollution and many of the risk factors for newborn deaths are influenced by similar sociodemographic factors that increase women’s risk of being exposed to air pollution. As such, women in countries with low levels of sociodemographic development are at risk for adverse birth outcomes, with related consequences for their children. Air pollution affects a child’s development, learning, and well-being throughout their lifetime.

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8. DOES GENDER IMPACT HOW AIR POLLUTION AFFECTS HEALTH AND WELL-BEING?

The effects of air pollution are not distributed equally among populations. Variables such as race, ethnicity, migrant status, informality, and age play a crucial role in determining both the level of exposure to air pollution at home and work, as well as the resulting health consequences and access to healthcare. To ensure fair and effective policymaking regarding air pollution, it is essential to understand and act on the uneven distribution of exposure and susceptibility to air pollution among different groups of people.

Gender plays a significant role in shaping the impact of air pollution on various populations. It influences how individuals spend their time, affecting their exposure to pollution, especially concerning work-related activities, leisure, and household responsibilities. A recent scoping review conducted by the Stockholm Environment Institute (SEI) examined existing research on air pollution's effects in the workplace in southeast and east Asia. The findings revealed that men bear a higher health burden from total air pollution exposure, possibly due to increased exposure to air pollutants in their workplaces. Conversely, the study highlighted that women and girls experience more exposure to household air pollution, stemming from traditional division of responsibilities. Apart from direct health consequences, air pollution can also have indirect effects on women and girls, leading to increased caregiving responsibilities for family members affected by pollution.

However, gender considerations are seldom incorporated into the design and implementation of policy responses to address air pollution issues. One of the contributing factors is the lack of disaggregated data, resulting in unequal outcomes for different groups. To address this issue, obtaining high-quality and timely data that is disaggregated not only by gender but also by other factors – such as income, age, ethnicity, and location - is crucial. This data is vital in identifying those who might be left behind and ensuring their inclusion in the decision-making process. By meaningfully integrating gender dimensions into the assessment of air pollution impacts and the development of mitigation measures, society as a whole can benefit, leaving no one behind in the quest for clean air.

The UNECE Convention on Long-range Transboundary Air Pollution has also provided threshold (critical) levels for ozone (O ₃ ) , above which, impacts on crops and other vegetation can occur.

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9. IS THERE A SAFE LEVEL OF AIR POLLUTION TO PROTECT YOUR HEALTH?

While all individuals experience different levels of health impacts from air pollution, across large city or country populations, there is no evidence of a completely safe level of air pollution, especially in the case of particulate matter and NO₂. However, to help guide countries achieve cleaner air for health, the WHO has set normative guideline values for all major air pollutants. Compliance with those values would protect public health from adverse effects. In 2021 the WHO published updated air quality guidelines for common air pollutants as well as interim target levels for PM (PM_2.5 and PM₁₀), O₃, NO₂, and SO₂.

This does not mean that there are no health effects below those guidelines; however, available studies do not include sufficiently large populations with exposure levels below those concentrations. The guideline values represent health-based targets useful for tracking the burden of disease from air pollution, informing national level targets and standards, and monitoring the effectiveness of air quality management efforts designed to improve health.

Many countries have established national air quality standards. National standards may differ from country to country and may be above or below the respective WHO guideline value. It is a policy issue to decide which specific at-risk groups should be protected by the standards, and what degree of risk is considered to be acceptable. However, the number of countries with no or insufficient regulations are still very high, especially in the developing world, and the new WHO values are indeed substantially lower. This means almost all countries will need to set strategies for further clean air policies towards meeting the WHO interim goals and ultimately its guideline values.

The UNECE Convention on Long-range Transboundary Air Pollution has also provided threshold (critical) levels for ozone (O₃), above which, impacts on crops, forest and grassland can occur.

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10. WHAT EFFECT DOES AIR POLLUTION HAVE ON FOOD, CROPS, FORESTS AND BIODIVERSITY?

Ozone (O₃) is by far the main air pollutant affecting plant growth. It reduces crop yields, forest health and biodiversity generally. Different plant species have different sensitivity to O₃; those more sensitive to O₃ will have reduced competitive advantage in ecosystems, while more resistant species will become more dominant. Some crops are very sensitive to O₃, especially beans and wheat. Soybean yields, for example, can be reduced by 15% or more. Yield losses due to O₃ might put pressure on crop markets and prices, thereby affecting crop availability and accessibility and hence regional food security. There is also a knock-on effect on the climate, as the reduced growth of forest trees caused by O₃ pollution, reduces the ability of forests to absorb carbon dioxide and their potential to help regulate climate change.

Other pollutants like sulphur and nitrogen can also damage forest and lake ecosystems through acidification of soils and surface water, affecting forest growth and killing fish and other organisms. Nitrogen deposition also causes eutrophication (over-fertilisation) of low nutrient ecosystems such as heathlands, causing large shifts in biodiversity.

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11. HOW IS ACID RAIN CONNECTED TO AIR POLLUTION?

Some air pollutants cause ‘acid rain’, a problem that received particular focus in Europe and North America in the 1980s and 90s. Sulphur dioxide (SO₂), ammonia (NH₃) and nitrogen oxides (NOx) react in the atmosphere, producing sulphuric acid, nitric acid and ammonium that return to earth as ‘acid rain’.

Acid rain impacts the environment by damaging the leaves of plants, thereby reducing plant productivity, and can strip the soil of the nutrients that plants need to survive. In the 1970s and 80s, acidification of soils and surface waters in sensitive catchments of Sweden led to massive loss of fish populations, causing a public outcry. Similar impacts were experienced across Scandinavia and other parts of Europe and Canada. Acid rain is also known to cause irreversible damage to buildings and monuments.

Acid rain in Europe and North America has reduced greatly because of stronger SO₂ and NOx emission controls, such as the U.S. Clean Air Act of 1970 , the Canada–United States Air Quality Agreement in 1991, and similar measures in Europe. While acid rain has decreased in Europe and North America, it remains a concern in Asia.

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12. HOW DO I KNOW THE LEVEL OF THE POLLUTION PROBLEM IN MY COMMUNITY?

Many cities have implemented monitoring networks that continuously measure air pollutants as part of their air quality management systems. Many regularly report an Air Quality Index (AQI) designed for public information purposes that is easy to interpret, and often color-coded, to warn of dangerous levels of air pollution. The information is accessible through websites, newspapers, and apps. Countries define their own indices based on their own air quality standards. Therefore, they are not comparable between countries. There are also a wide variety of AQIs available globally, which are also not readily comparable.

The availability of air quality monitoring is unequal globally and regionally. This is because high quality monitors are expensive, as is the cost of training people to run and maintain monitoring networks. Even in places with good monitoring, there are discrepancies. For example, in some parts of Europe, there are very dense monitoring networks, while in other parts the networks are less dense. In many developing countries across the world there is no official air pollution monitoring.

Investing in air quality monitoring is very important because the larger the networks are, the more information we can have for a city, a region, or country. This information can be invaluable for helping people understand the air pollution levels where they live and take action to reduce their exposure. It’s also important for governments, to be able to make short and long-term planning decisions to reduce air pollution. According to UNEP’s first global assessment of air quality legislation, 37% of countries do not currently require monitoring mechanisms in their national air quality management systems.

In many places, private companies are developing lower-cost air quality monitors that people can install in their own homes. This is leading to networks of citizen scientists reporting on air quality and citizen led online air quality databases. Though these datasets are growing, the data must be used with caution for individual and public decision making. A number of international and civil society organizations and private companies also collect and report air quality information, often based on a combination of monitoring and satellite data. Where local information is unavailable, these can be useful resources to understand the air pollution problem in your city or country. For example, the WHO Air Quality Database compiles data on ground measurements of air pollutants from over 8,600 human settlements in more than 120 countries. The database is updated every 2-3 years and was last updated in May 2023.

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13. HAS AIR POLLUTION BEEN SOLVED ANYWHERE?

Air pollution has not been solved in any region, but there have been remarkable decreases in emissions and pollutant concentrations in many European countries, as well as the USA, Canada, and Japan, where strong policies, regulations and regular monitoring systems have been put into place.

One of the most famous examples is London, which had some of the worst levels of pollution, earlier than other cities, probably peaking in the year 1900. Since then, air quality in the UK has improved remarkably. Particulate air pollution levels fell by over 97% between 1900 and 2016. Other cities and regions have also shown significant reductions, brought about by similar policies. However, this does not mean that air pollution has been solved. In London PM_2.5 remains higher than the WHO air quality standard.

Beijing, once notorious for its air pollution problem, has in the last 20 years taken increasingly aggressive steps to reduce air pollution and its air quality has improved substantially. Similarly, in 1992, Mexico City was labelled as the world’s most polluted city, but in 1995 the government launched an extensive programme named ProAire with concrete measures to increase public awareness and achieve sustainable development in eight areas including reduction of energy consumption, cleaner and more efficient energy and promotion of public transport. Mexico City’s air pollution has decreased by nearly 60% since the introduction of ProAire. From a peak in 1989, O₃ levels decreased by two-thirds by 2015 – still high enough to cause significant health impacts, but a massive reduction nevertheless.

Aerosols and photochemical oxidants (like ozone) can also create haze and reduce visibility, which can shroud cities in dense smog. During the London Smog Disaster (see question 3) and similar pollution episodes, visibility was extremely low. The strong link between visibility and pollution was illustrated when people in parts of Northern India could see the Himalayas for the first time in a generation, when air pollution levels fell due to the lock-down and reduced emissions, caused by the COVID-19 crisis. Falling concentrations in North America and Europe has reduced this haze significantly, but it is very prevalent in other parts of the world, especially in Asia.

These decreases show that air pollution is a problem that we know how to solve, and that there are policies and technologies needed, and indeed in principle available, to achieve cleaner air. In many countries, improved air quality has happened while countries have increased in wealth. This means that unlike in the past, where air pollution was considered an unavoidable cost of economic growth, air pollution reduction does not impact economic growth. It is effectively decoupled from wealth creation.

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14. WHAT ACTIONS CAN GOVERNMENTS TAKE TO IMPROVE AIR QUALITY?

Governments are responsible for providing their citizens with clean air. There are multiple options for national and local governments to improve air quality. Air pollution is a problem that we know how to solve.

Air pollution impacts everyone and its sources and solutions are diverse. Actions to reduce air pollution require cooperation among various sectors and stakeholders (including the general public), different levels of government, and among governments and regions. However, clean air strategies vary in approach according to the context of each country and city, as well as its capacity to develop and implement control measures. There is not one uniform policy prescription for air quality that is applicable to all cities, countries and regions; such an approach would be neither possible nor desirable for a problem that is so diverse in local circumstances.

Governments should invest in capacity to measure and monitor air pollution by establishing monitoring networks and ensuring that such networks are properly operated, maintained, and subjected to procedures that guarantee the quality and reliability of air quality measurements.

The first step towards responsible management of air pollution is to make sure that necessary laws, regulations, policies, and enforcement mechanisms are in place and sufficiently supported. Governments should ensure that the appropriate institutions have sufficient capacity to monitor and assess air pollution emissions. This will ensure that decision makers know where their air pollution comes from, how large the different sources of emissions are, the levels of air pollution in different parts of their country, the impacts on health, and what high impact actions can be taken to reduce pollution levels and reduce the harm caused.

Where capacity to undertake such activities is limited or local data is not available, there are still resources available to help countries understand their air pollution problem and identify priority actions that can be taken. These include sources for emissions, estimated by global programmes (e.g. EDGAR emission estimates), or concentrations and health impacts (WHO, IHME, State of Global Air), estimated from satellites and global modelling, with ground truthing from monitoring stations. These datasets have their limitations and uncertainties and should be used in the cases where local data are not available, or where there is limited monitoring capacity.

It is important that governments understand the benefits and costs associated with alternative actions or interventions to improve air quality; and to prioritize actions. Most air pollution reduction measures have health and social benefits that far outweigh the costs of implementation.

Strengthening institutions and governance, promoting behavioural change, instilling a pro-clean air culture, increasing the capacity in all sectors to effectively engage and contribute to solutions, political will, and increased funding, are also key elements of success.

Last but not least, it is of utmost importance and duty that governments inform the general public about the policies, measures and technologies being used to monitor and reduce air pollution – and to provide easy-to-understand analyses of the impacts these actions have on air quality. A simple and effective way to interact with the public and create a sense of ownership of solutions to the problem of air pollution are citizen science approaches, which have been successfully trialed in developed and developing countries.

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15. WHY IS REGIONAL COOPERATION CRUCIAL FOR MANAGING AIR POLLUTION?

Since some air pollutants travel long distances and across borders, a multi-national/regional approach is important to manage cross-border air pollution. International cooperation facilitates knowledge sharing of experiences and good practices, and raises the profile and resources needed to address the air pollution crisis, at a scale consistent with the magnitude of the problem.

A good example of the positive achievements of a multi-national intergovernmental air pollution reduction approach is the UNECE Convention on Long-range Transboundary Air Pollution, which was the first coordinated approach between countries to address their common and shared air pollution problems. Scientific cooperation has also been initiated in Asia, and the Acid Deposition Monitoring Network in East Asia (EANET) has been building capacity and cooperation on monitoring across East and Southeast Asia. The Asia Pacific Clean Air Partnership has been fostering knowledge sharing on solutions to address air pollution in the region. The Association of Southeast Asian Nations (ASEAN) Agreement on Transboundary Haze Pollution has been developed to limit the air pollution from forest fires in Southeast Asia. The Ministers of Environment of the Latin America and the Caribbean region adopted a Regional Action Plan on Air Quality in 2014 and updated in 2022 support countries' efforts to implement low-cost air quality monitoring networks, as well as policies and strategies for controlling air pollution, recognizing synergies with the energy conservation and climate change agenda. In 2022, the UNESCAP Regional Action Programme on Air Pollution was adopted to respond to the regional and transboundary challenges posed by air pollution.

Another example is the global monitoring plan for persistent organic pollutants (POPs). This is an important component of the effectiveness evaluation of the Stockholm Convention and provides a harmonized organizational framework for the collection of comparable monitoring data on the presence of POPs from all regions, in order to identify changes in their concentrations over time, as well as on regional and global environmental transport. Monitoring results supports the informed decision making of Parties to the Stockholm Convention in identifying, characterizing, quantifying and prioritizing sources of releases of unintentional POPs, and developing strategies with concrete measures, timelines and goals to minimize or eliminate these releases.

The development of regional agreements to address the shared problem of transboundary air pollution

During the 1960s, scientists found that the deposition of air pollutants, often emitted thousands of kilometres away, were causing the ‘acid rain’ that was affecting forests, causing acidification and associated fish loss in lakes, and putting entire ecosystems at risk in parts of the Northern Hemisphere, particularly in Scandinavia, Canada and Scotland.

Two landmark conferences in the 70s, the United Nations Conference on the Human Environment and the Helsinki Conference on Security and Cooperation in Europe, paved the way for negotiations on an intergovernmental agreement to reduce air pollution.

In 1979, 32 countries signed the UNECE Convention on Long-range Transboundary Air Pollution: the first international treaty to deal with air pollution on a broad regional basis. Entering into force in 1983, the Convention laid down the general principles of international cooperation for air pollution reduction and set up an institutional framework that has brought together science and policy.

With 40 years of experience, 51 Parties in the Northern Hemisphere and 8 Protocols in force today, the results of the work under the Convention so far, have been significant. The Convention is unique in that it provides an international legally binding agreement, which sets emission reduction targets for several pollutants. It provides a platform for countries to discuss policies and to exchange best practices. The Convention counts on a solid science-policy interface, a compliance mechanism and a capacity-building support programme.

In order to share the lessons learned and successes from the Convention and to facilitate mutual learning, the Convention has recently set up the Forum for International Cooperation on Air Pollution (FICAP) which will provide a means for all countries and regions globally, to cooperate and collaborate on reducing the impacts of air pollution on health and nature.

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16. WHAT IS THE ROLE OF AIR QUALITY MONITORING IN AIR QUALITY MANAGEMENT?

Countries face several challenges when addressing air quality. The cost of certified monitoring equipment, as well as regular calibration and maintenance, can be a heavy burden to many local authorities and national governments. It is important to note that the cost of air quality monitoring is much lower than the cost of air pollution reduction, the former being a public investment and the latter a private investment. It therefore makes sense for national governments and cities in developing countries to prioritize and invest in the establishment, operation, and maintenance of ground-level air quality monitoring networks, to generate reliable data on air quality.

Many countries have no government-run monitoring networks using regulatory-standard equipment at all. In countries with limited resources, monitoring sites are often only located in their largest, most populated city. Many cities in developing countries can only afford to have a single monitoring site, or a few at most. This is something that needs to be addressed.

In many places, private companies are developing lower-cost air quality monitors that people can install in their own homes. This is leading to networks of citizen scientists reporting on air quality and citizen led online air quality databases. Though these datasets are growing, the data have to be used with caution for the individual and public decision making. A cross-calibration of these low-cost sensors with high quality, regulatory monitoring devices is strongly recommended, as is a double or triple installation of low-cost sensors at each location for purposes of comparison (faulty devices can then be easily detected). Recently, successful approaches of combining a small number of high-precision regulatory monitoring devices with a large number of low-cost sensors to record the air pollution concentration across the area of entire cities have been developed.

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17. WHAT ACTIONS CAN BUSINESSES AND INDUSTRY TAKE TO REDUCE AIR POLLUTION?

Businesses and industry have a key role to play in reducing air pollution, since many of their activities produce different types of air pollutants. The private sector can contribute to air pollution reduction through its various operations and supply chains across different sectors. Pollution sources from the private sector range from burning fuels, to distribution and delivery vehicles. Since air pollution also contributes to climate change, companies that pledge to reduce their air pollution emissions can simultaneously reduce their carbon footprint. This double win reducing air pollution and their carbon footprint can and has been the driver of innovative solutions from the sector. In the past, these solutions have mostly been technological (e.g. switching from one technology to another), but some parts of the private sector may need to move beyond those technological solutions. There are several actions the private sector can take to reduce air pollution:

Add air quality to their Corporate Social Responsibility activities and pledge to regular reporting and monitoring.
Identify, quantify, and report air pollution emissions along with co-emitted greenhouse gases from separate facilities, manufacturing processes and supply chains.
Establish programmes that reduce air pollution, specific to each sector including implementation of best available techniques and best environmental practices and adopting measures to improve energy efficiency.
Promote awareness campaigns to transparently communicate the levels of emissions caused by their operations and explain what they will do to reduce those emissions.

One example of how a large industry can act to reduce air pollution is presented in a report by the International Aluminium Institute (IAI), ‘Sustainable Bauxite Mining Guidelines’, which includes air quality.

World Economic Forum’s Alliance for Clean Air : the first global corporate initiative to bring together leading businesses to tackle air pollution.

Launched at COP26 by the World Economic Forum, in partnership with the Clean Air Fund, the Alliance’s founding members include Accenture, Bloomberg, Biogen, Google, GoTo, IKEA, Maersk, Mahindra Group, Siemens and Wipro. The Alliance has now grown and includes, Oracle, EY, Moderna, Haleon, GSK, and GEA.

Alliance members commit to:

Establish air pollution footprints on nitrogen oxides, sulphur oxides and particulate matter within 12 months.

Pinpoint where they are being emitted to track human exposure

Set ambitious targets and objectives to reduce the air pollution emissions, with a clear action plan

Act as champions for clean air by raising awareness among employees, customers and communities about the impact of air pollution. They will also help them to reduce their exposure and support them to take action to reduce pollution

Use their assets innovatively to accelerate clean air solutions

Alliance members are implementing a practical guide for businesses on how to quantify air pollutant emissions across value chains. This Guide is, being developed by the Stockholm Environment Institute, Climate and Clean Air Coalition, in co-operation with IKEA.

Five of the Alliance members have already published their air pollutant emissions as part of their sustainability reports including IKEA, Maersk, GoTo, Bloomberg, and Biogen.

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18. WHAT CAN I DO TO IMPROVE AIR QUALITY IN MY COMMUNITY?

Most sources of air pollution are structural and embedded in the economic processes underpinning modern society. Even in countries and communities with strong air pollution policies, individuals may not always have access to technologies or transportation options to meaningfully impact air pollution on their own. It will take a collective effort.

The most important thing people can do is to get informed about the levels of air pollution where they live and how it affects them, and to put pressure on politicians, leaders, and decision makers to reduce air pollution in their city, region, or country.

Some of the things individuals can do to reduce their personal contribution to air pollution are:

Choose clean modes of transport when available (e.g. public transport, cycling or walking rather than private cars or motorbikes)
If you’re considering buying a car, look at its fuel economy, nitrogen dioxide emissions, and check the real-world emissions. Buying a hybrid or electric vehicle or smaller engine capacity vehicles will also help to cut down your contributions to emissions
Use clean (low and ultra-low Sulphur) fuels together with advanced vehicle emissions control technologies identified above
If you have a car, ensure it is serviced regularly to minimize its contribution to air pollution
Use clean fuels and technologies for cooking, lighting and heating
Use renewable energy sources wherever possible
Stop burning household and agricultural waste
Eliminate fireplace and wood stove use
Monitor your energy demand and waste at home and install energy-efficient appliances and light bulbs, insulation and draught-proof windows
Support policies, economic incentives and regulations which increase access to the actions/choices above
Join a local group of citizen scientists to help monitor local air quality and support data collection and reporting to build an evidence-base for action (see Question 12).

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19. HOW ARE AIR POLLUTION AND CLIMATE CHANGE CONNECTED?

Air pollution and climate change are inherently linked. All major air pollutants have an impact on the climate and most share common sources with greenhouse gases (GHGs), especially related to the combustion of fossil fuels. They also aggravate each other in multiple ways. For example, the dangerous GHG methane contributes to the formation of ground-level-ozone, and levels of ground-level ozone increase with rising temperatures. Rising temperatures increase the frequency of wildfires, which in turn further elevate levels of particulate air pollution.

One increasingly important link between air pollution and climate change are wildfires which are increasing around the globe in frequency, severity, and duration. With climate change leading to warmer and drier conditions, the fire season is starting earlier and ending later. Wildfires are increasingly more extreme, burning larger areas and with greater duration and intensity. Wildfire smoke is a mixture of hazardous air pollutions and can also impact the climate by releasing large quantities of CO2 and other greenhouse gases into the atmosphere. According to Europe’s Copernicus Atmosphere Monitoring Service (CAMs), Canadian wildfires emitted 290 Mt of carbon into the atmosphere between 1 January and 31 July 2023, nearly double the previous record for the year as a whole.

Methane is a potent greenhouse gas that forms ozone in the atmosphere. Reducing methane is one of the most cost-effective strategies to rapidly reduce the rate of warming while simultaneously protecting human health and crop yields. Integrated actions, such as those that target SLCPs, can therefore provide triple-win scenarios by achieving real-world multiple benefits for human health, agriculture and the climate.

The interlinkages between air pollution and climate change provide an opportunity to amplify the benefits of our actions and catalyse even greater mitigation ambition. At the same time, not all air pollution reduction strategies are beneficial for climate, and vice versa. Win-win strategies to rapidly reduce warming must therefore integrate actions to reduce all air pollutants and greenhouse gases that contribute to both near- and long-term climate impacts. This will put the world on a trajectory that maximizes benefits, reduces the risk of policy failure, and delivers national development priorities.

Methane is a clear multi-win option for air quality and the climate

The IPCC Sixth Assessment report identified methane as a clear option for achieving substantial near- and long-term avoided warming while simultaneously achieving air quality benefits by reducing ground-level ozone concentrations. Methane is a an extremely powerful greenhouse gas, responsible for about 30 per cent of warming since pre-industrial times. Unlike CO₂ which stays in the atmosphere for 100s of years, methane starts breaking down quickly, with most of it gone after a decade. This means cutting methane emissions now can rapidly reduce the rate of warming in the near-term. Because methane is a key ingredient in the formation of ground-level ozone (smog), a powerful climate forcer and dangerous air pollutant, a 45 per cent reduction would prevent 260 000 premature deaths, 775 000 asthma-related hospital visits, 73 billion hours of lost labour from extreme heat, and 25 million tonnes of crop losses annually.

Recognizing the importance of rapid methane abatement, since 2021, over 100 countries, representing more than 50% of global anthropogenic methane emissions and over two thirds of global GDP have joined the Global Methane Pledge. Participating countries have agreed to act to reduce global methane emissions at least 30 per cent below 2020 levels by 2030.

For more information:

Global Methane Assessment: Summary for Decision Makers

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20. HOW IS AIR POLLUTION CONNECTED TO SUSTAINABLE DEVELOPMENT?

Air pollution is a threat to sustainable development, as it simultaneously affects various social, environmental, and economic criteria linked to equitable human development, such as good health, food security, gender equality, climate stability and poverty reduction.

Progress on air quality results in multiple development benefits. Several SDGs are linked to air quality, including SDG target 3.9 on good health and well-being, SDG target 7.1.2 on access to clean energy for cooking, SDG target 11.6.2 on air quality in cities, SDG target 11.2 on access to sustainable transport, and SDG 13 on climate action.

Air pollution is also at the heart of social justice and global inequality. According to the World Health Organization (WHO), 97 per cent of cities with more than 100,000 inhabitants in low- and middle-income countries do not meet air quality guidelines. That percentage falls to 49 in high-income countries.

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21. IS CLEAN AIR A HUMAN RIGHT?

In 2022, the United National General Assembly adopted Resolution 76/300, recognizing the right to a clean, healthy, and sustainable environment as a human right. Resolution 76/300 recognizes air pollution as one of the factors which interfere with the enjoyment of a clean, healthy and sustainable environment. The Resolution follows a similar landmark recognition by the UN Human Rights Council in October 2021, which recognized for the first time that having a clean, healthy, and sustainable environment is a human right. These resolutions build on a 2019 report by the Special Rapporteur for Human Rights and the Environment which highlighted seven steps that States must implement, to fulfil the right to breathe clean air.

The UN resolutions are not legally binding, but can be a powerful catalyst for action and expansion of legal developments in a large number of jurisdictions. For example, in at least 155 countries, a healthy environment is recognized as a constitutional right. Obligations related to clean air are implicit in a number of international human rights instruments, including the Universal Declaration of Human Rights and the International Covenant on Economic, Social and Cultural Rights.

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22. HOW DO WILDFIRES CONTRIBUTE TO AIR POLLUTION?

Smoke from wildfires as well as other landscape fires used for land clearing and agriculture are a major contributor to air pollution, contributing to roughly 4 per cent of global PM_2.5. In many countries of the world, this number can be up to 10–60 per cent. Extreme fire smoke events can lead to very high levels of air pollution over a one to two week periods, easily the highest levels experienced throughout the year in affected locations.

The summer of 2023 has already seen devastating and record-breaking wildfires across much of the northern hemisphere including Northern Africa, Greece, Spain, Portugal, Turkey and other parts of Europe, Canada, the western U.S., and large parts of eastern Russia. At least 34 people were killed and thousands evacuated to escape wildfires in Algeria and parts of Tunisia. Wildfires burning on the Hawaiian island of Maui have displaced thousands of residents, destroyed parts of the centuries-old town, Lahaina, and killed at least 96 people. According to the Canadian Interagency Forest Fire Centre, as of 8 August 2023, more than 13 million hectares of forests have already burnt compared to the 10-year average of about 800,000 hectares.

The Australian bushfires in 2019 and 2020 burned more than 12 million hectares of land, exposed more than 10 million people to hazardous PM_2.5 levels, led to the direct loss of 33 lives, the destruction of 3,500 houses, and significant wildlife and habitat loss. Wildfire smoke clearly leads to a worsening of pre-existing respiratory disease, such as asthma and chronic obstructive pulmonary disease (COPD), with emerging evidence of impacts on cardiovascular disease, increased complications for those with type 2 diabetes as well as links between in utero exposure and low birthweight babies. The economic cost of the smoke-related health impacts alone from the 2019/20 Australian bushfire season was estimated to be nearly 2 billion AUS.

It is not yet known whether discrete smoke episodes that are experienced year after year have cumulative impacts, although evidence from air pollution in general suggests this is also likely. From the perspective of overall, population-level impacts, an analysis conducted in 2012, estimated that smoke from landscape fires accounted for approximately 10 per cent of the estimated annual deaths attributable to particulate matter air pollution.

As wildfire smoke events will increase with a warmer climate and given that these are inherently more difficult to control at the source compared with other common air pollution sources, there is a need for adaptation strategies. Communities in wildfire-prone areas must plan for clean-air shelters, while individuals, especially the most susceptible, can use HEPA filter portable air cleaners to reduce exposures and ensure they have sufficient medication to last through a prolonged wildfire season.

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