Air pollution may have links to suicide, a new study reveals.

This first of its kind large-scale study published in the National Bureau of Economic Research examined deaths across the US between 2003 and 2010.

It found that an increase in daily PM2.5 - a fine particulate matter capable of entering the bloodstream via the lungs - of one microgram per cubic metre was associated with an almost 0.5 per cent increase in daily suicides.

A monthly PM2.5 increase at the same level was associated with a 50 per cent rise in suicide-related hospitalisations.

Why is air pollution dangerous?
Air pollution is associated with 7 million premature deaths every year, according to the World Health Organization. It has been shown to increase the risk of respiratory infections, heart disease and lung cancer, and may even alter foetus development.

There is also growing evidence that air pollution also affects the brain and behaviour.

Small particulate matter can enter the lungs and reduce the flow of oxygen into the bloodstream. Studies have shown this could impact productivity, strategic choices, academic performance and mental health.

How can air pollution impact mental health?
The relationship between air pollution and mental health may have a biological explanation.

Exposure to fine particulate matter can greatly increase levels of cytokines - neurotransmitters produced in response to infection and inflammation that are also associated with depression and suicide. Pollution has been associated with inflammation of the brain, which may disrupt mood regulation.

Researchers Persico and Marcotte of Washington DC’s American University set out to explore the impact of air pollution on mood in more depth.

They matched daily data on suicide counts by county to air quality data, using wind direction as an instrument for pollution exposure.

The study was controlled for local unemployment, population, weather, holidays, county, month and time of week.

As well as finding increases in daily suicide rates and monthly suicide-related hospitalisations, the study discovered that heightened levels PM2.5 are linked to more self-reported depressive symptoms.

Is air pollution high in Europe?
According to the European Environment Agency, air pollution is the single largest environmental health risk in Europe, causing potentially deadly cardiovascular and respiratory diseases.

Despite improvements in air quality across the EU, in 2019 and 2020 air pollutants often exceeded EU air quality standards and WHO guideline levels.

Exposure to air pollutants varies by country and environment. Those living in big cities tend to be exposed to higher concentrations of nitrogen dioxide due to traffic emissions.

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In central and eastern Europe, solid fuels burnt for domestic heating and industry result in the highest concentrations of particulate matter and the carcinogen benzo[a]pyrene.

Southern Europeans are exposed to the highest concentrations of ozone, the formation of which is driven by sunlight.

In the European Union, 97 per cent of the urban population is exposed to levels of fine particulate matter above guideline levels set by the World Health Organization.

Air quality improved slightly in 2020, most likely due to weather patterns and the impact of COVID-19 lockdowns.