Air pollution has reached dangerous levels across multiple cities and regions of the world, according to a coordinated set of reports released on June 4, 2021, with public health consequences that researchers describe as one of the most serious and under-appreciated environmental health challenges facing the world today. The reports — prepared by the World Health Organization, specialist research institutions, and a coalition of national health and environmental agencies — describe a situation in which billions of people are exposed to air quality that exceeds safe limits, with specific populations facing particularly acute exposures and with specific health consequences that produce millions of preventable deaths each year.

The scale of the problem documented in the reports is striking. The majority of the world's population lives in areas where ambient air pollution exceeds the levels that the World Health Organization identifies as safe, with specific urban populations facing particularly high exposures. Indoor air pollution — often produced by the burning of solid fuels for cooking, heating, and lighting in households that lack access to cleaner alternatives — affects additional billions of people, with specific health consequences that fall disproportionately on women and children in affected households. Taken together, ambient and household air pollution constitute one of the largest environmental health risks facing the global population, and the specific health burden they produce continues to be measured in millions of annual deaths.

The Specific Pollutants of Concern

The reports describe the specific pollutants that produce most of the health burden attributed to air pollution. Fine particulate matter — particles with diameters of 2.5 micrometres or less, commonly referred to as PM2.5 — has emerged as the single most important air pollutant from a public health perspective. These particles are small enough to penetrate deep into the lungs and, in specific cases, to enter the bloodstream. Their specific chemical composition varies depending on their sources, and specific forms of PM2.5 — including those derived from diesel exhaust, from coal combustion, from specific industrial processes, and from specific natural sources — can produce different specific health effects.

Nitrogen dioxide, produced primarily by the combustion of fossil fuels in vehicles, power plants, and specific industrial operations, has been identified as a specific contributor to respiratory and cardiovascular disease. Ground-level ozone, formed through the specific photochemical interaction of various precursor pollutants with sunlight, produces specific respiratory effects and is particularly concerning during the specific periods of hot weather when its formation is most active. Sulphur dioxide, carbon monoxide, and specific categories of volatile organic compounds each contribute to the overall air pollution burden in specific ways.

Household air pollution is dominated by specific pollutants produced by the burning of solid fuels — including wood, charcoal, coal, dung, and specific agricultural residues — in inefficient stoves. The specific mix of pollutants produced by household fuel combustion is particularly hazardous because of the direct exposure of household members during the specific periods of cooking, heating, and lighting. The specific populations most affected by household air pollution — typically women who perform the majority of cooking and the young children who spend time in kitchens — face cumulative exposures that produce substantial health consequences.

Health Consequences

The specific health consequences of air pollution extend across multiple organ systems and affect populations in multiple specific ways. Respiratory diseases — including chronic obstructive pulmonary disease, asthma, acute lower respiratory infections in children, and lung cancer — have specific documented links to air pollution exposure. Cardiovascular diseases, including ischaemic heart disease and stroke, account for a substantial proportion of the total health burden attributed to air pollution, reflecting the specific ways in which fine particles affect blood vessels, blood clotting, and specific aspects of cardiovascular function.

Cancer effects extend beyond lung cancer to include specific other cancers for which air pollution has been identified as a risk factor. Neurological effects — including specific impacts on cognitive development in children and specific associations with neurodegenerative conditions in adults — have been the subject of growing research attention. Specific effects on maternal and infant health, including specific associations with low birth weight, preterm birth, and specific developmental outcomes, have been documented in multiple studies. Mental health effects, including specific associations with depression and other psychiatric conditions, have emerged as a specific area of research interest.

The specific distribution of health consequences across populations is uneven. Children, whose respiratory systems are still developing and who breathe more air per unit of body weight than adults, face specific vulnerabilities. Older adults, whose physiological reserves are reduced and who often have pre-existing conditions that air pollution can exacerbate, face specific risks. People with existing respiratory and cardiovascular conditions face specific exacerbations and complications. Pregnant women and the infants they are carrying face specific exposures with potentially lasting consequences. And specific populations — often those in lower-income communities, specific minority groups, and residents of particular neighbourhoods — face disproportionately high exposures, producing specific environmental justice concerns that have become central to the air pollution policy debate.

The Sources of the Problem

The specific sources of air pollution vary widely across contexts, and the specific mix of sources in any particular location shapes the specific interventions that will be most effective. Transport is a major contributor in most urban areas, with specific vehicle emissions — particularly from diesel vehicles — producing specific impacts on local air quality. Power generation, particularly from coal and other fossil fuels, is a major source in regions where these fuels dominate the electricity mix. Industrial operations, including specific manufacturing processes, cement production, and specific extractive activities, produce specific emissions that affect particular locations.

Household energy use, as already noted, is a major source of air pollution in contexts where solid fuels are widely used. Agricultural activities, including specific crop burning practices, specific livestock operations, and specific fertiliser applications, contribute particularly to specific rural air pollution problems. Natural sources — including wildfires, dust storms, and specific volcanic activity — produce specific episodic contributions that have been intensifying in some regions as a result of climate change and specific land-use changes.

The specific geographic distribution of sources affects the specific patterns of exposure. Cities with heavy industry and high vehicle traffic typically experience the highest ambient pollution levels. Communities located near specific pollution sources — including highways, industrial facilities, and specific other point sources — experience particularly high exposures. Regional and trans-boundary pollution transport means that specific populations downwind of major source areas can experience significant pollution from sources located far from them.

Policy Responses

Policy responses to air pollution have been advancing in multiple jurisdictions, with specific approaches reflecting the specific characteristics of each context. Regulatory limits on specific emissions — including specific standards for vehicles, for power plants, for industrial operations, and for specific other sources — have been tightened in many jurisdictions, though specific implementation and enforcement has been uneven. Specific air quality standards, which establish the concentrations of particular pollutants that should not be exceeded in ambient air, have been established and periodically revised.

Specific interventions focused on particular sources have been advancing. Vehicle emissions controls — including specific standards for new vehicles, specific programmes to remove high-polluting older vehicles from circulation, and specific arrangements for low-emission zones in urban areas — have been producing measurable benefits in specific contexts. Power sector policies — including specific closures of coal plants, specific investments in renewable energy, and specific other measures — have been reducing emissions from electricity generation. Industrial emissions controls, specific regulations on household fuels and stoves, and specific measures addressing agricultural sources have all been advancing in various forms.

Specific investments in monitoring infrastructure have been critical to the policy response. Dense networks of air quality monitors, supplemented by specific satellite-based observations and specific low-cost sensor networks, have been producing increasingly detailed data about the specific patterns of pollution exposure. This data has supported specific targeted interventions, has enabled specific research on pollution health effects, and has provided the specific factual basis on which policy decisions are made.

Transition to cleaner energy has been a central element of the longer-term response. Specific policies promoting renewable electricity, specific programmes supporting access to clean cooking fuels in lower-income contexts, specific electrification of transport, and specific other energy transition measures produce air quality co-benefits alongside their specific climate and development benefits. The specific integration of air quality considerations into broader energy and climate policy has been advancing in many jurisdictions, with specific evidence that integrated approaches produce better outcomes than treating air quality as a separate policy domain.

What Individuals Can Do

The reports include specific guidance for individuals on reducing their own exposure and supporting the broader policy response. Specific actions include checking local air quality information and adjusting specific activities — including outdoor exercise, open windows, and specific outdoor time for children — when pollution levels are high. Specific protective measures — including specific types of face masks that filter fine particles, and specific air purification for indoor environments — can reduce exposure in specific circumstances, though their specific effectiveness varies and their use is not a substitute for addressing the sources of pollution.

For individuals whose specific activities contribute to air pollution, specific choices can reduce their contribution. Transport choices — including specific decisions about vehicle type, about modes of transport for particular trips, and about the specific management of personal vehicles — affect specific emissions. Energy choices in the home — including specific decisions about heating, about appliances, and about specific energy sources — similarly affect specific emissions. Consumption choices more broadly shape the specific industrial and agricultural activities that contribute to pollution.

Civic engagement — supporting specific policies, advocating for specific interventions, and participating in the specific decision-making processes that shape local and national air quality policy — is another dimension of what individuals can contribute. Public pressure has historically been a significant driver of specific air quality improvements, and the specific political economy of air pollution response reflects the balance between specific economic interests associated with pollution-producing activities and the broader public interest in clean air.

The Climate Connection

The connection between air pollution and climate change is a specific feature of the current policy landscape that has received particular attention in recent years. Many of the specific sources of air pollution — including fossil fuel combustion, specific industrial processes, and specific agricultural activities — are also major sources of greenhouse gas emissions. Specific policies addressing climate change, including the phase-out of fossil fuel use, also produce air quality co-benefits, and specific policies addressing air quality can support the broader climate agenda.

Specific pollutants — including specific categories of short-lived climate pollutants such as black carbon, methane, and specific hydrofluorocarbons — have both climate and air quality implications. Specific interventions targeting these pollutants can produce both climate benefits and air quality benefits on different timescales, with specific air quality improvements emerging quickly and specific longer-term climate benefits accumulating over decades. The specific concept of integrated climate-air-quality policy has been advancing, with specific analytical frameworks and specific policy initiatives that bridge the two agendas.

At the same time, climate change is affecting air quality in specific ways that complicate the policy response. Rising temperatures increase the formation of ground-level ozone. Climate-driven wildfires are producing specific air quality emergencies in specific regions. Specific changes in dust storm patterns and in specific other natural sources are affecting air quality in ways that will need to be addressed alongside the specific human sources of pollution.

International Cooperation

International cooperation on air pollution has been advancing in specific ways. Regional agreements — including specific arrangements addressing long-range transboundary air pollution in Europe, North America, and specific other regions — have produced measurable reductions in specific pollutants through specific coordinated action. Global frameworks, including those developed under the auspices of the World Health Organization and the United Nations Environment Programme, have supported specific national efforts and have promoted specific best practices.

Specific international research collaborations have been advancing the scientific understanding of air pollution and its health effects. Networks of researchers, often supported by specific international funding mechanisms, have been producing specific studies that inform policy in multiple jurisdictions. The specific work of translating research into policy — through specific guidance documents, specific technical assistance to governments, and specific support for capacity-building — has been a particular focus of international organisations.

International support for air quality improvement in lower-income contexts has been a specific focus. Specific development assistance, specific investments by multilateral development banks, and specific partnerships with private-sector actors have been supporting specific air quality projects, particularly those addressing household air pollution and those supporting the energy transition in specific contexts. The specific scale of this international support has been growing but remains below the levels that analyses suggest would be appropriate given the scale of the need.

Looking Ahead

The reports are explicit that air pollution, while a serious challenge, is also a challenge for which effective responses exist. Specific interventions — across the specific sectors that contribute to pollution, across the specific pollutants of greatest concern, and across the specific populations most affected — have been producing measurable improvements in specific jurisdictions. The specific record of air quality progress in specific cities and countries over recent decades demonstrates what is possible when sustained commitment meets adequate resources.

The specific work of achieving similar progress on a global scale will require sustained attention across the many actors whose decisions shape air quality outcomes. Governments at national, regional, and local levels. Industries whose operations affect emissions. Financial institutions whose investments support specific energy and industrial activities. Civil society organisations whose advocacy and research shape the broader policy environment. Individual citizens whose specific choices and engagement shape the political context within which policy is made.

For the billions of people currently exposed to dangerous levels of air pollution, the specific experience includes not only the general unpleasantness of breathing polluted air but also the specific health consequences that accumulate over time, often in ways that are not obvious in any single day's exposure. The specific work of reducing those exposures produces benefits that are often quiet and cumulative rather than dramatic, but that are measured — over time — in longer lives, better health, and the specific opportunities that good health makes possible.

A Preventable Burden

The specific message of today's reports is consistent with the broader pattern of air pollution analysis over recent decades. The specific health burden produced by air pollution is substantial. The specific sources are well understood. The specific interventions that can reduce exposures and associated health effects are largely known. What is required is the sustained commitment, at scale, to implement those interventions across the specific contexts where they are needed.

Today's reports argue that current responses, while meaningful, are insufficient to the scale of the challenge. They make specific recommendations for accelerating progress, and they identify specific actors whose choices will shape the trajectory. The specific response to these recommendations — in specific policy decisions, specific investments, specific commitments, and specific actions — will determine how much of the current burden can be reduced in the coming years.

The tools exist. The knowledge exists. The specific frameworks for action exist. What is required is the sustained commitment to deploy them at the scale the situation demands. That is the message, in the end, that today's reports are asking their readers to hear — and the work that the coming years will either accomplish or fail to accomplish, with consequences that will be measured in billions of lungs, in millions of lives, and in the specific quality of the air that every person breathes every day.