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ClientEarth Communications

12th August 2021

Air pollution
Healthy Air Campaign

How is air pollution caused?

Air pollution is caused when processes, like burning fossil fuels, release certain gases and chemicals into the air that have harmful or poisonous effects.

Sources of air pollution vary, but the World Health Organization (WHO) lists major outdoor pollution sources as residual energy from heating and cooking, vehicle exhaust fumes, generating power, agriculture and waste incineration, and industry. The chemicals generated by these processes, which can be considered as pollutants, include particulate matter, sulphur dioxide, nitrogen oxide, benzene and carbon monoxide.

Typically, the primary causes of the air pollution problem in industrialised and industrialising countries are the following:

Burning fossil fuels

Historically, the main contributor to air pollution has been high levels of smoke and sulphur dioxide, as a result of burning fossil fuels like coal. This process releases nitrogen oxides into the atmosphere, which contribute to the formation of smog and acid rain.

Vehicle emissions

Now, one of the main threats to clean air is the pollutants caused by car exhaust fumes and other vehicle emissions. Carbon monoxide, nitrogen oxide, volatile organic compounds (VOCs) and particulate matter are all released by both petrol and diesel vehicles, and have an increasingly negative impact on the air quality of urban areas. Rural areas also suffer from this type of air pollution, as the VOCs and nitrogen dioxide react with sunlight to form ozone, a secondary pollutant, which spreads far from the areas in which it originated.


There is also a level of background air pollution that can be attributed in part to agriculture and industry, which causes vast amounts of ammonia to be emitted.

Ammonia emissions can spread across continents. As it travels, ammonia reacts to create yet more fine particulate matter (PM2.5), tiny particles that can enter the bloodstream through the lungs. These particles pose a major threat to health, affecting nearly every organ in the human body.

Why is air pollution a problem for our health?

It’s estimated that roughly 90% of the world’s population lives in areas where air pollution levels exceed WHO limits. The WHO states that ambient air pollution accounts for around 4.2 million deaths per year, causing and exacerbating conditions like heart disease, lung cancer, acute and chronic respiratory diseases, and strokes. New research recently found that in 2018, the number of global deaths from air pollution was up to 8.7 million. In the UK, air pollution is the biggest environmental threat to health, with Public Health England estimating that long-term exposure causes between 28,000 and 36,000 deaths a year.

How are air pollution and climate change linked?

A great number of air pollution sources are also those of greenhouse gas (GHG) emissions. Greenhouse gases cause the earth’s heat to be trapped in the atmosphere, which leads to warmer temperatures. These warmer temperatures affect our planet in many ways, causing rising sea levels, extreme weather and increased transmission of infectious diseases.

Air pollution is made worse by climate change, as air pollution in the form of smog, for example, worsens the warmer the temperature is, forming when there is more ultraviolet radiation. Higher temperatures also increase the production of allergenic air pollutants, including mould and pollen. This means that, as much progress as we have made through the introduction of initiatives like clean air zones (CAZ) and low emissions zones, as climate change worsens, so will air pollution.

More on air pollution

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