A new study including data from some 1,400 air quality monitoring stations across China has found that suicide rates rise as air quality declines. It also shows how a nationwide, government-led plan to reduce air pollution helped prevent tens of thousands of suicides in just a few years.

China has some of the most polluted cities in the world, its metropolises blanketed in thick smog that hangs heavy over millions of urban inhabitants.

Around 16 percent of worldwide suicides occur in China, although the country's rates have declined substantially in recent years. There are a few reasons why that might be, from increasing incomes to cultural shifts. But the new study from a team of economists who combined air quality data and reports of deaths by suicide reveals with greater clarity than ever before how closely breathing bad air and suicide rates are linked.

In 2013, China was facing a "herculean task to control air pollution" so it introduced its Air Pollution Prevention and Control Action Plan, which clamped down on industrial sources of pollution, regulated vehicle emissions, promoted a switch from coal to natural gas for heating, and encouraged a transition to solar and wind power, leading to marked improvements in air quality.

At the same time, suicide rates declined sharply across the country. Between 2010 and 2021, the annual suicide rate dropped from 10.88 to 5.25 suicides per 100,000 people, according to the Chinese Center for Disease Control and Prevention (CCDC).

Peng Zhang, an economist at the Chinese University of Hong Kong, and colleagues took advantage of these "striking" trends to see if they could isolate the effects of air pollution on suicide risk from other factors linked to suicide.

To do so, they dug into weekly air quality data and honed in on a meteorological phenomenon called thermal inversions, which trap air pollution close to the ground in a layer of cold air pinned down by a hotter band above.

These inversions typically last only a few hours, but at a county level they can raise the weekly average concentration of fine particulate matter in the air (known as PM2.5) by about 1 percent, Zhang and colleagues found.

Previous research has shown how these small particles can travel directly to the brain, altering its chemistry in as little as 24 hours and leading to poorer mental health and possibly worse emotional regulation in the long run.

Building on those studies, which provide a plausible mechanism linking air pollution and suicides, Zhang and colleagues observed a clear and sudden uptick in suicide rates within a week of thermal inversion events, but the effect did not last beyond 7 days.

"These are 'additional' suicides – deaths that would otherwise never have occurred had air quality not deteriorated," the researchers write in their published paper.

The good news is roughly 10 percent of China's recent downward trend in suicide rates is attributable to reducing air pollution. That amounts to nearly 46,000 suicide deaths prevented between 2013 and 2017 because of efforts to clear China's skies, the researchers estimate.

"While there remain many open questions regarding the connections between air quality, mental health and suicide, this analysis adds urgency to calls for pollution control policies across the globe," the team writes.

The study may be confined to China, and only show a correlation between smog and suicide rates, but we should all heed its findings knowing that almost nowhere on Earth has consistently safe levels of air pollution anymore.

The study has been published in Nature Sustainability.

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