Air Pollution: Global Assessment And Ambient Impacts

Ambient air pollution is a growing concern, with an increasing number of acute episodes in cities worldwide. It is a major risk factor for global disease, increasing morbidity and mortality. The World Health Organization (WHO) has published a global assessment of exposure to ambient air pollution and the resulting burden of disease. This report summarises the methods and results of the latest assessment, providing important insights for policy development to reduce the health effects of air pollution. The assessment combines satellite-based estimates, chemical transport model simulations, and ground measurements to produce global estimates of fine particle (PM2.5) and ozone concentrations. These estimates allow for the evaluation of trends and the assessment of the impacts of air pollution on population health relative to other risk factors.

The history of air pollution

Air pollution has been a growing concern in recent years, with a rise in the number of acute air pollution episodes in cities worldwide. The World Health Organization (WHO) has been actively monitoring and addressing this issue for almost 50 years, with the aim of reducing health risks caused by air pollution.

In the past, air pollution was mainly an issue in industrial areas, with smoke and smog being common occurrences. However, with the rise in motor vehicle usage, pollution spread beyond these localized areas. This led to the recognition of air pollution as a widespread environmental issue, impacting both human health and the planet.

The effects of air pollution are far-reaching, with fine particulate matter causing strokes, heart diseases, lung cancer, and acute and chronic respiratory diseases. It is also a significant contributor to climate change, with many of the drivers of air pollution, such as the combustion of fossil fuels, being sources of greenhouse gas emissions. According to WHO estimates, 4.2 million people died in 2019 due to poor air quality, developing cardiovascular diseases as a result.

To address this global health emergency, the WHO has been compiling ground measurements of air quality, specifically focusing on the annual mean concentrations of particulate matter. The organization has developed an Ambient Air Quality Database, which currently includes data from 4300 human settlements in 108 countries. This database provides essential information for countries to establish baselines, track progress, and advocate for actions to improve air quality.

In addition to data collection, the WHO promotes interventions and initiatives for healthy sectoral policies, including energy, transport, housing, and urban development. By providing technical support and guidance to member states, the WHO is actively working towards reducing the health and environmental impacts of air pollution.

Health impacts

Ambient air pollution is a major environmental health problem affecting people in low-, middle-, and high-income countries. In 2019, it was the largest environmental risk to health, causing an estimated 4.2 million premature deaths worldwide per year. This mortality is primarily due to exposure to fine particulate matter, which results in cardiovascular and respiratory disease, strokes, and cancers.

The World Health Organization (WHO) has identified particulate matter (PM) as a common proxy indicator for air pollution, with strong evidence linking it to negative health impacts. The major components of PM include sulfates, nitrates, ammonia, sodium chloride, black carbon, mineral dust, and water. Exposure to PM can lead to increased risks of heart disease, stroke, chronic obstructive pulmonary disease (COPD), lung cancer, and pneumonia.

Carbon monoxide (CO), another harmful pollutant, is a colorless, odorless, and toxic gas produced by the incomplete combustion of carbonaceous fuels such as wood, petrol, charcoal, natural gas, and kerosene. Ground-level ozone (O3), formed through the reaction of gases in the presence of sunlight, is a major constituent of photochemical smog. Nitrogen dioxide (NO2) is commonly released from fuel combustion in the transportation and industrial sectors. These pollutants contribute to the overall degradation of air quality and pose significant health risks.

The health impacts of ambient air pollution are not limited to physical ailments but also extend to mental health. Studies have found associations between air pollution and adverse mental health outcomes, including increased rates of depression, anxiety, and cognitive decline. Prolonged exposure to air pollutants can lead to chronic inflammation and oxidative stress, which have been linked to the development of mental health disorders.

Addressing ambient air pollution is crucial not only for public health but also for climate change mitigation. Many of the drivers of air pollution, such as the combustion of fossil fuels, are sources of greenhouse gas emissions. Implementing policies and investments that support sustainable land use, cleaner household energy, cleaner transport, energy-efficient housing, and better waste management can effectively reduce key sources of ambient air pollution. By reducing air pollution, we not only improve public health but also contribute to mitigating the impacts of climate change.

Household air pollution

The health risks associated with household air pollution are significant. Exposure to indoor smoke and the fine particulate matter it contains can cause both short-term and long-term health issues. Short-term effects include eye irritation, coughing, and nose and throat irritation. More seriously, the fine particulate matter and pollutants in indoor smoke can cause inflammation in the airways and lungs, impairing immune response and reducing the oxygen-carrying capacity of the blood.

The long-term health consequences of household air pollution exposure are even more concerning. It is a known risk factor for several non-communicable diseases, including ischaemic heart disease, stroke, chronic obstructive pulmonary disease (COPD), and lung cancer. In children under five years old, exposure to household air pollution is particularly dangerous, contributing to almost half of all pneumonia deaths in this age group. It is also associated with an increased risk of lower respiratory infections, which is the leading cause of childhood deaths from pneumonia. Additionally, emerging evidence suggests that household air pollution may contribute to other health issues such as low birth weight, stillbirth, asthma, ear infections, upper respiratory infections, tuberculosis, and various cancers.

The impact of household air pollution disproportionately affects women and children in low- and middle-income countries. They typically bear the burden of household chores, such as cooking and collecting firewood, which exposes them to harmful pollutants for extended periods. Furthermore, the use of open fires and inefficient stoves for cooking and heating can also lead to safety risks, including burns, scalds, and poisoning from kerosene, which is often stored in refilled soda bottles.

Addressing household air pollution is crucial for improving global health and reducing premature deaths. The WHO has issued guidelines for indoor air quality, providing evidence-based recommendations on clean fuels and technologies. These include the use of solar, electricity, biogas, liquefied petroleum gas (LPG), natural gas, alcohol fuels, and biomass stoves that meet emission targets. Additionally, sustainable land use, cleaner household energy and technologies, energy-efficient housing, and improved waste management practices can effectively reduce household air pollution and its associated health risks.

Global health observatory data

Ambient air pollution data is critical to enabling public action and global health initiatives. The World Health Organization (WHO) has been actively gathering air quality data since 2011, with ground measurements of the annual mean concentrations of particulate matter. This data is compiled in the WHO Ambient Air Quality Database, which is updated regularly every 2-3 years. The database includes information on nitrogen dioxide (NO2) and particulate matter of a diameter equal to or smaller than 10 μm (PM10) or 2.5 μm (PM2.5). These pollutants originate primarily from human activities related to fossil fuel combustion.

The WHO uses urban measurements to represent human exposure to air pollution, including data from urban backgrounds, residential, commercial, mixed, and rural areas, as well as industrial areas close to urban settlements. This comprehensive approach ensures that the data represents an average for an entire city or town rather than individual stations. The database serves as a valuable resource for countries and the global community to establish baselines, track progress, draw comparisons, and advocate for necessary actions to improve air quality.

The WHO also publishes a report titled "Ambient Air Pollution: A Global Assessment of Exposure and Burden of Disease." This report summarizes the methods and results of WHO's global assessment of ambient air pollution exposure and its health impacts. It highlights the growing concern of air pollution, with an increasing number of acute episodes in cities worldwide. As a result, data on air quality is becoming more available, and the science underlying the health impacts is rapidly evolving.

The Air Pollution Data Portal, maintained by the WHO, includes Burden of Disease statistics, air quality databases, and modelled exposure estimates for both ambient and household air pollution. This portal provides essential information for official reporting, such as world health statistics and Sustainable Development Goals. According to the latest WHO estimates, 4.2 million people died in 2019 due to poor air quality, and an additional 4.2 million developed cardiovascular diseases, lung cancer, or COPD.

Additionally, the WHO Ambient Air Quality Database App provides easy access to WHO data. The app includes built-in data from the database, with the latest update released in January 2024 (Version 6.1). This app enables users to access global assessments and information on efforts to reduce health risks caused by air pollution. Overall, the availability of global health observatory data on ambient air pollution is crucial for raising awareness, informing policy decisions, and driving actions to mitigate the health impacts of air pollution worldwide.

WHO interventions and initiatives

The World Health Organization (WHO) has developed several interventions and initiatives to address the global issue of ambient air pollution, which is a major environmental health problem affecting individuals in low-, middle-, and high-income countries. Here are some key interventions and initiatives undertaken by the WHO:

Global Air Quality Guidelines (AQG)

The WHO has established Global Air Quality Guidelines (AQG) that provide global guidance on thresholds and limits for critical air pollutants that pose health risks. These guidelines are developed through a transparent, evidence-based approach and offer interim targets to encourage a gradual reduction in pollutant concentrations, ultimately improving health outcomes. For instance, achieving interim target one (35 µg/m3) is estimated to save around 300,000 lives annually worldwide. The AQG also provides qualitative statements on the management of specific particulate matter, such as black carbon, ultrafine particles, and particles from sand and dust storms.

Monitoring and Data Collection

WHO actively monitors ambient air pollution exposure levels and their health impacts, including mortality and reduced life expectancy, at the national, regional, and global levels. This data is essential for official reporting, such as the World Health Statistics and the Sustainable Development Goals. The Air Pollution Data Portal, for example, offers a wealth of information, including Burden of Disease statistics, air quality databases, and modelled exposure estimates for both ambient and household air pollution.

Global Conferences and Commitments

The WHO organizes global conferences to address air pollution and its impact on public health. For instance, the Second WHO Global Conference on Air Pollution and Health concluded with significant commitments to protect public health on March 28, 2025.

Guidelines for Clean Fuels and Technologies

In 2014, the WHO released the first-ever health-based guidelines on clean fuels and technologies for household cooking, heating, and lighting. These guidelines aim to reduce the impact of household air pollution, which, when combined with ambient air pollution, contributes to approximately 6.7 million premature deaths annually worldwide.

Policy Recommendations

The WHO emphasizes the need for concerted action by policymakers at the local, national, and regional levels to address outdoor air pollution. This includes promoting policies and investments that support cleaner transport, energy-efficient homes, improved power generation, and better waste management practices. These interventions can significantly reduce key sources of outdoor air pollution and improve air quality globally.

Frequently asked questions