Air pollution may harm cognitive intelligence, study says

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, BBC News reports.

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.

The study was based on measurements of sulphur dioxide, nitrogen dioxide and particulates smaller than 10 micrometres in diameter where participants lived. It is not clear how much each of these three pollutants is to blame.

Carbon monoxide, ozone and larger particulates were not included in the study.

Described as an invisible killer, air pollution causes an estimated seven million premature deaths a year worldwide, according to the World Health Organization.