Researchers believe the results have global relevance, with more than 80% of the world's urban population breathing unsafe levels of air pollution.
Chronic exposure to air pollution can cause harm to cognitive performance, a new study reveals. Researchers believe that the negative impact increases with age, and affects men with less education the worst.
Over four years, the maths and verbal skills of some 20,000 people in China were monitored by the US-Chinese study.
Researchers believe the results have global relevance, with more than 80% of the world's urban population breathing unsafe levels of air pollution.
Described as an invisible killer, air pollution causes an estimated seven million premature deaths a year worldwide, according to the World Health Organization. Pollution also increases the risk of degenerative diseases such as Alzheimer's and other forms of dementia, the study suggests.
Exposure to high levels of polluted air "can cause everyone to reduce their level of education by one year..., which is huge," one of the co-authors, Xi Chen of the Yale School of Public Health, told the Guardian newspaper.
Previous studies found air pollution had a negative impact on students' cognitive abilities.
In this study, researchers tested people of both sexes aged 10 and above between 2010 and 2014, with 24 standardised maths questions and 34 word-recognition questions.
One of the reasons the researchers suggest older men with less education were worst affected by chronic exposure to air population is because those subjects often work outdoor manual jobs.
Air pollution around the world - the stats
* About seven million people die every year from exposure to polluted air
* Air pollution caused 4.2 million deaths globally in 2016
* 91% of the world's population lives in places where air quality exceeds WHO guideline limits
* 14 Indian cities are among the world's 20 most polluted, with the northern city of Kanpur topping the list
* Nine out of 10 people in the world breathe polluted air
- Source: BBC News, WHO
