Chapter

Air pollution: A global health crisis

1.1 Scope of the report

This report provides an overview of the risks to the health of children resulting from exposure to air pollution, from the womb to late adolescence. It summarizes data on the exposure and the burden of disease of children worldwide, emphasizing the gross inequality of risk among different populations. It also describes effective, evidence based interventions that could be used in the health and other sectors to promote clean air for children’s health. These include use of the whole-of society primary health care approach to reduce the health risks posed to children by air pollution (5–7).

Protecting children from air pollution requires actions both to reduce air pollution and to improve children’s health. These include action on different scales by various institutions and actors in a range of health-determining sectors, from energy to transport to urban planning.

While this report is intended for stakeholders in various sectors, the health sector has critical leading roles in the fight to protect children from air pollution. Its roles include informing policy-makers about how to improve air quality, improving children’s health, raising awareness and empowering people to take action for cleaner air. One of the most important roles of the health sector is advocacy for implementation and enforcement of air quality standards in line with WHO guidelines.

The document mainly addresses outdoor and household air pollution, thus excluding certain sources of indoor air pollution, which can pose serious health risks to children’s health, such as from building materials, equipment and furniture. WHO has published detailed guidelines and public health recommendations on such sources (8).

1.2 A child’s right to clean air and its lifelong benefits

Nearly 2.4 billion children under the age of 18 – over 90% of all children – breathe polluted air that exceeds the WHO recommended annual limit of 5 µg/m3 for fine particulate matter; while 930 million are compelled to breathe outdoor air at concentration seven times higher (and equivalent to WHO interim target of 35 µg/m3 ) than the WHO recommended limit (9,10). In addition, 800 million children living in LMIC are exposed to household air pollution due to lack of access to clean cooking fuels and technologies. Every polluted breath increases children’s risks of respiratory illness, impaired development and premature death. These are not just health failures – they are violations of children’s fundamental rights to a clean, healthy, sustainable environment. Air pollution is a public health crisis for the world’s children.

Every polluted breath that a child takes puts their health, well-being and development at risk. It violates their fundamental rights to a clean, healthy, sustainable environment, as enshrined in the Convention on the Rights of the Child (11). The Convention – the world’s most widely ratified human rights treaty – affirms that children have the fundamental rights to grow and realize their full potential. In August 2023, the Committee on the Rights of the Child confirmed that every child has a right to clean air (12). The Convention also declares that children have the right to pursue legal action to compel their governments to “counter climate change and other forms of environmental degradation, including air pollution.”

The right to clean air has lifelong implications. Children exposed to air pollution are at higher risk of developing acute respiratory illness and noncommunicable diseases (NCDs) later in life. Emerging evidence shows the importance of a life course approach for full assessment of the impacts of air pollution on children’s health and well-being and of the cumulative effects of environmental exposures, from the womb through infancy, early childhood, adolescence and into adulthood (13).

Ensuring that children have access to clean air is essential to securing these fundamental rights and to giving them an opportunity to lead long, healthy, productive lives (14)

1.3 Sources of air pollution

Children are exposed to air pollution in many settings, at home, in the classroom, on the way to school, while performing household chores or playing outdoors (Table 1). In these environments that are critical to their growth and development, they may encounter a wide range of harmful air pollutants from a wide variety of both anthropogenic and natural sources, although anthropogenic sources account for the vast majority of air pollution emissions.

This report addresses the pollutants that account for most of the burden of disease from ambient air pollution and household combustion: particulate matter (PM2.5 and PM10 ), NO2 , SO2 and O3 . See the Glossary for more information on specific air pollutants.

1.4 Growing global challenges

Air pollution is the single largest environmental health risk for children. It harms nearly every organ in the body, contributes to child mortality and is a major driver of NCDs, with tobacco use, unhealthy diets, alcohol misuse and physical inactivity. Despite important progress in many countries to improve air quality through strategic policies and investments, the threat of air pollution is only getting worse for too many children (15).

On a global scale, the trends in air pollution have remained largely unchanged over the past 10 years, and many regions of the world are still far from meeting the WHO AQG (Fig. 1). Air pollution, specifically from fine particulate matter (PM2.5 ), remains a significant, pervasive global health threat, disproportionately affecting large populations in LMIC.

The challenges posed by accelerating urbanization, inequity and climate change are global, with concrete effects on the daily lives of children.

1.4.1 Urbanization

Urbanization and unsustainable consumption and production are increasing exposure to air pollution in many parts of the world. The proportion of the global population – including children – living in urban areas continues to grow rapidly (17). In such environments, children may be exposed to higher concentrations of air pollution from a wide array of sources, from vehicles to industry to waste incineration to fossil fuel combustion for indoor cooking and heating. About 7 200 cities in 123 countries monitor air quality for regulatory purposes (collected in the WHO Ambient Air Quality database), and only about 1% of those cities in LMIC meet the WHO AQG for PM (18). Thus, children in cities in LMIC are 23 times more likely than those in high-income countries to live in areas that do not meet air quality standards. Effective management of urban growth, including urban health planning, is essential to ensure sustainable development, especially in regions in which urbanization is expected to increase rapidly.

1.4.2 Inequity

Inequitable distribution of exposure to air pollution and the associated disease remains troublingly persistent, both within and among countries. Children in LMIC bear the heaviest burden. Poverty is strongly associated with exposure to higher levels of pollution and adverse health outcomes. Despite reductions in extreme poverty over the past three decades, children are still more than twice as likely as adults to live in extreme poverty (19), and exposure to pollution is increasing in some LMIC. Polluting industries, waste disposal sites and high-traffic roads are often situated in low-income communities, where children face disproportionately high risks but may lack adequate access to health care or to cleaner household fuels. They may also be less resilient to the health impacts of air pollution due to other environmental exposures and social factors.

Demographic transitions exacerbate such inequity. Those parts of the world in which the threat of air pollution is most acute (Africa and Asia) are those in which the child population is largest and growing fastest (15).

1.4.3 Climate change

Climate change is impacting almost every aspect of child health and well-being, from pregnancy to adolescence. The health impacts are compounded by climate-related hazards, which often overlap (20). Climate change and air pollution are closely interlinked: atmospheric warming worsens air quality, and certain kinds of air pollution cause further warming. Rising temperatures degrade and interact with air quality in many ways, directly and indirectly, with combined effects that pose hazards to children’s health (21,23–25).

Periods of hot, sunny weather promote production of ground-level O3 from its precursor gases; they also increase levels of airborne pollen and allergens, which are increased by rising levels of carbon dioxide. Stagnant conditions can prevent dispersion of PM in the air. Drought dries soil and vegetation, resulting in airborne dust. Hot, arid conditions promote more frequent, more severe wildfires, which in turn worsen air quality. As wildfires increase in frequency and extent, they emit carbon dioxide, methane, PM and other toxic pollutants into the atmosphere – degrading air quality further and fuelling further warming. The combined effects of heat and poor air quality can increase adverse impacts on respiratory and cardiovascular health (23,26–28).

These two global health crises also have common causes. Fossil fuel combustion is the primary driver of the climate crisis and is a major source of air pollution (29). Health-damaging air pollutants are often emitted with climate-warming greenhouse gases from power plants, vehicles, industrial activities and building heating systems based on fossil fuels. Cooking and heating with polluting fuels result in both health-damaging emissions and net additions of greenhouse gases

1.5 Costs of inaction and opportunities for action

1.5.1 The costs of inaction

Reducing children’s burden of disease and death due to air pollution should be considered not as an expense but as an investment. Although incremental but encouraging progress toward cleaner air is being made in many parts of the world, the situation is urgent, as inaction results in staggeringly high costs. Air pollution places an enormous strain on health systems and has severe economic and societal costs. In 2019, the global health cost of air pollution due to PM2.5 was US$8.1 trillion (33).

In 46% of the countries in the UN Economic Commission for Europe, it is estimated that ambient air pollution produces damage to health (reduced life expectancy, hospital admissions, sick leave and medical costs) and ecosystems to over 5% of gross domestic product. In at least six of those countries the damage is equivalent to more than 10% of gross domestic product (34).

These estimates do not capture the full cost of children’s burden of disease from air pollution, as exposure early in life can contribute to diseases that emerge only in adulthood. The estimates also do not include losses in human capital, including long-term impacts on educational attainment, cognitive development, workforce productivity and intergenerational earnings.

Conversely, cleaning the air children breathe will have immense benefits in terms of avoided illness, associated health-care costs and productivity losses. Some of these benefits will manifest immediately, while others will multiply over time, freeing human potential and enabling an entire generation to grow into healthy, flourishing adults.

1.5.2 Opportunities for action in the Sustainable Development Goals agenda

Clean air for children is part of the agenda for the SDGs (36). Wider implementation of evidence-based policies and interventions to protect children from air pollution is essential to achieving many of the SDG targets (Fig. 2), including reducing maternal and child mortality and achieving universal access to energy.

SDG 3, to “ensure healthy lives and promote well-being for all at all ages”, addresses children’s environmental health and includes targets to end preventable deaths of newborns and children under 5 years by 2030 and also to reduce mortality attributable to ambient and household air pollution. Relevant indicators: SDG 3.2.1, 3.2.2 and 3.9.1.
SDG 7 addresses household air pollution, which disproportionately affects children and Fig. 2 Relation of air pollution to the SDGs women, especially those in LMIC, and calls for universal access to clean, sustainable energy. Relevant indicator: SDG 7.1.2.
Other elements of the SDG agenda that are closely linked to children’s environmental health, include sustainable urban environments (SDG 11), gender equality (SDG 5), responsible consumption and production (SDG 12) and climate action (SDG 13). Relevant indicator: SDG 11.6.2.

Placing children at the centre of the SDG agenda and policies is essential as:

Intervening in childhood has lifelong, intergenerational benefits.
Investments in achieving the SDGs can improve both clean air and children’s health.
All sectors are responsible for children’s well-being.

As reflected in several recent World Health Assembly and UN Environment Assembly resolutions, countries are already committed to improving the health and well-being of children by:

accelerating progress towards achievement of the SDG targets for maternal, newborn and child survival (37);
scaling up primary prevention for environmental health (38,39);
combatting air pollution by strengthening regional cooperation (40);
directly addressing the health effects of air pollution (41); and
providing a mandate to WHO to enhance the delivery of primary health care (42).

The 78th World Health Assembly recently adopted an updated road map to address the health effects of air pollution (44). Decision-makers in all sectors and at all levels must build on this progress and momentum to provide clean air for the world’s children

1.6 The WHO air quality guidelines

1.6.1 WHO global air quality guidelines

The WHO The WHO AQG represent global targets to be reached by national, regional and city governments to improve their citizens’ health by reducing air pollution. The guidelines consist of evidence-based recommendations to limit the levels of specific air pollutants. They were developed to help countries achieve air quality that is protective of public health. The guidelines were first released in 1987 and are updated regularly to ensure their continued relevance by including studies on the effects of air pollution on health published since the previous update. They provide a broad range of policy options for air quality management. The latest version was published in 2021 (44).

The 2021 WHO AQG recommended levels and interim targets for common air pollutants, PM, O3 , NO2 , sulfur dioxide and CO, are listed in Table 1.

While not legally binding, the AQG are published to guide governments in setting legally enforceable air quality standards and to guide environmental health authorities and professionals tasked with protecting people from the harmful effects of environmental air pollution. The guidelines are intended to be used in diverse conditions in all WHO regions and to provide a basis for a broad range of policy options for air quality management. Knowledge about the hazardous properties of air pollutants and indications of the risk related to exposure provide an essential scientific foundation for air quality management.

1.6.2 WHO Guidelines for indoor air quality: Household fuel combustion

Household air pollution is one of the largest environmental risk factors for children’s health worldwide. The WHO guidelines for indoor air quality: household fuel combustion (45) offer clear, practical recommendations to ensure that increasing access to clean household energy results in substantial health gains.