Is air pollution making us stupider?

Students who take exams amid heavy air pollution may perform worse than those who take the same test on a clear day, according to a study that claims that air pollution is causing a “huge reduction in intelligence”.

The report, published in the Proceedings of the National Academy of Sciences, compared the results of language and maths tests conducted on 20,000 people across China between 2010 and 2014 with data measuring levels of nitrogen dioxide and sulphur dioxide in the air.

Researchers identified a correlation between high pollution levels and “significant drops in test scores in language and arithmetic”, The Guardian reports, with the average effect on intelligence “equivalent to having lost a year of the person’s education”.

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The impact was particularly severe on the elderly, which could have “serious consequences” for major financial decisions made late in life, Sky News reports.

Young people may also be at risk, as the study “suggests that high levels of air pollution have a short-term impact on intelligence, meaning students may perform worse if they take important exams on polluted days”.

The longer the subjects had been exposed to unclean air, the larger the reduction in their recorded cognitive ability on the tests.

Although the study was carried out using data from Chinese subjects, the findings have global ramifications. Earlier this year, a report by the Health Effects Institute found that 95% of the world’s population breathe unclean air.

Xiaobo Zhang, of Peking University, one of the authors of the study, told CNN that the findings were alarming for developing countries, where air quality is particularly poor.

“The damage on cognitive ability by air pollution also likely impedes the development of human capital,” he said, suggesting that “the indirect effect of pollution” on the welfare of newly industrialising nations “could be much larger than previously thought”.

Aarash Saleh, a doctor of respiratory medicine and an anti-pollution campaigner, said the new study adds to a “concerning bank of evidence” linking exposure to unclean air with poorer cognitive function.