Muhammad Hammad

Most people on Earth are exposed to unhealthy levels of air pollution. Each year, millions of people die early, and many more live with debilitating chronic diseases because of breathing polluted air.

The threat of air pollution is not new, but it is changing. Air pollution has contributed to death and disease and has hurt economic prospects and community resilience for decades. During that time, policies and technologies have drastically improved air quality in some areas, saving lives, and proving that pollution is not an inevitable by-product of economic development.

Yet despite this encouraging progress, the threats posed by air pollution have continued to mount as they merge with the threats posed by global climate change and increasingly aging populations.

Exposure to Air Pollution

Air pollution is a complex mixture of particles and gases with sources and composition varying over space and time. While hundreds of chemical compounds can be measured in the air, governments typically measure only a small subset as indicators of the different types of air pollution and major sources contributing to that pollution.

Sometimes referred to as criteria pollutants, these pollutants include particulate matter, nitrogen dioxide, sulphur dioxide, ozone, and carbon monoxide, and are known to harm our health and ecosystems. PM2.5, NO2, and ozone are the three indicators used to quantify air pollution exposures in the GBD study.

Fine Particle Air Pollution

Fine particle air pollution, or PM2.5, refers to airborne particles measuring less than 2.5 micrometres in diameter (less than a 30th of the diameter of a human hair). These particles, as well as precursor chemicals that contribute to their formation in the atmosphere, are emitted from vehicles, residential fuel use, coal-burning power plants, agricultural and industrial activities, waste burning, wildfires, and many other human and natural sources.

PM2.5 Trends

Globally, ambient PM2.5 levels are decreasing or stabilizing in many regions. The global average exposure for ambient PM2.5 in 2020 was 31.3 μg/m3. The highest annual average exposures were seen in South Asia; East, West, Central, and Southern Africa; North Africa; and the Middle East.

Nitrogen Dioxide

Nitrogen dioxide (NO2) is a gaseous air pollutant that is mainly generated through the burning of fuel in vehicles, power plants, and industrial facilities.

It belongs to a group of reactive gases known as nitrogen oxides and is often used as an indicator for this group and for the broader traffic-related air pollution mixture. Because traffic is a major source of NO2, its concentration is typically highest in urban areas and is considered a marker for the broader traffic-related air pollution mixture. In addition to traffic, agriculture is another important source of nitrogen oxides.

Ozone

Ground-level, or tropospheric, ozone is a pollutant that harms human health, damages plants, and contributes to climate change. Globally, ozone levels are estimated to be 30%–70% higher today than they were 100 years ago. This trend reflects rising emissions of the chemicals that form ozone as well as rising temperatures.

Ozone is not released directly into the air but is formed through chemical interactions between nitrogen oxides and volatile organic compounds (VOCs) in the presence of sunlight. The burning of fossil fuels in vehicles, power plants, factories, and homes and through industrial activities (such as oil and gas extraction and processing) produces precursor chemicals.

Air Pollution’s Burden of Disease

Exposure to air pollution is associated with impacts on every major organ system in humans. To inform actions that can save lives, it is critical to understand the risks faced by particular groups, the impacts of different pollutants, and the changes over time.

Over many decades, scientific studies have documented a wide range of health effects from air pollution. While high-pollution days can have short-term effects, like aggravating asthma symptoms, and lead to temporary spikes in hospitalizations for heart or lung problems, the most severe impacts are caused by long-term exposures.

Breathing polluted air for months or years can lead to illness and early death from heart and lung diseases and diabetes as well as increase the likelihood of adverse birth outcomes, including preterm births, stillbirths, and miscarriages.

The Global Burden of Air Pollution

Taken together, air pollution from PM2.5 and ozone was estimated to contribute to 8.1 million deaths— about 12% of the total global deaths — in 2021. PM2.5 (both ambient and household together) is the largest contributor to the air pollution disease burden worldwide, accounting for 7.8 million deaths, or more than 90% of the total air pollution disease burden.

Disease Burden of PM2.5

PM2.5 air pollution is the largest driver of air pollution‘s burden of disease worldwide. Long-term exposure to PM2.5 pollution is associated with illness and early death from diseases, including heart disease, lung cancer, COPD, stroke, type 2 diabetes, lower respiratory infections (such as pneumonia), and adverse birth outcomes.

It is estimated that ambient PM2.5 and household air pollution (i.e., household PM2.5) together contributed to 7.8 million deaths globally in 2021, with ambient PM2.5 accounting for 4.7 million deaths and household air pollution accounting for 3.1 million of all the deaths attributable to ambient PM2.5 in 2021.

Disease Burden of Nitrogen Dioxide

There is a large and growing body of scientific evidence linking NO2 pollution with a variety of health effects. Short-term exposure to NO2 can irritate the airways and aggravate existing respiratory diseases. For people with asthma, NO2 exposure is associated with more frequent and severe asthma symptoms and a greater risk of hospitalization.

Studies also have suggested that exposure to NO2 pollution can impair lung development, intensify allergies, and make people more susceptible to respiratory infections, and several studies indicate that children exposed to NO2 pollution are at a greater risk of developing asthma.

Disease Burden of Ozone

Short-term exposure to ozone is linked to asthma exacerbation and other respiratory problems. Long-term exposure to ground-level ozone is linked with the development of COPD.

In adults, a progressive and debilitating disease that makes breathing harder; COPD is a major global cause of death and disability. In 2021, long-term exposure to ozone contributed to an estimated 490,000 deaths from COPD worldwide. This loss of life equates to 8.7 million or 13% of all COPD deaths globally.

Air Pollution and Children’s Health

Children are the future, yet early exposure to air pollution poses a major threat to the well-being of children around the world. Air pollution was the second leading risk factor for death among children under five in 2021, after malnutrition.

Impacts on Neonatal Health

Being exposed to air pollution in the womb increases the likelihood that a baby will be born too small (low birth weight) or too early (preterm birth). These conditions, in turn, make babies more susceptible to lower respiratory and other serious infections, diarrheal diseases, brain damage and inflammation, blood disorders, and jaundice.

If the babies survive infancy, they remain at a higher risk for LRIs, other infectious diseases, and major chronic diseases throughout life. Exposure to air pollution during pregnancy has also been linked to miscarriage, stillbirths, and congenital disorders and anomalies.

Impacts in Children under Five

Breathing polluted air early in life can have both immediate and long-term implications for a child‘s health. Air pollution affects children‘s health through its role in pneumonia and other respiratory infections and allergic diseases. LRIs are the leading cause of death for children under five. Exposure to air pollution can make a person more susceptible to infections in the lungs by causing inflammation and weakening the body‘s defences against viruses and bacteria.

Household air pollution is an important risk factor for pneumonia. Such infections during childhood can also result in long-term health effects, including impaired lung growth and a higher risk for chronic diseases later in life.

Air Pollution and Childhood Asthma

Some of the well-studied impacts of pollution exposure in young children relate to asthma, the most common chronic respiratory disease in children. People with asthma suffer symptoms such as wheezing, trouble breathing, chest tightness, and cough, sometimes in acute episodes or as ―asthma attacks,‖ which can be life-threatening.

Air pollution‘s impacts in terms of quality of life, medication costs, loss of school days, and frequent hospital visits impose substantial social and economic burdens on children, their families, and health systems. In this context, it is important to note that asthma prevalence is not studied in nearly half of the countries, and in many LMICs, asthma diagnosis and treatment are not yet common. In children who have an asthma diagnosis, there is strong evidence that breathing polluted air can worsen the symptoms and trigger asthma attacks.