Air pollution may reduce intelligence. Research in China showed that air pollution led to big falls in test scores for languages and arithmetic. The study is called, "The impact of exposure to air pollution on cognitive performance". It took place over four years. Researchers looked at speaking and arithmetic tests taken by 20,000 people of all ages. They said: "Polluted air may impede cognitive ability as people become older."
The study is a warning to people in cities. Over 91 per cent of us live in areas with toxic air, which is the fourth biggest cause of global deaths. The longer people are exposed to polluted air, the greater their intelligence goes down. Air pollution may cause a year's worth of lost education. This could be several years for older people. A researcher warned: "Governments really need to take concrete measures to reduce air pollution."