BBC: Pollutants in the air we breathe have been classed as a leading environmental cause of cancer by the World Health Organization.
It said the evidence was clear they cause lung cancer.
Sources of pollution include car exhausts, power stations, emissions from agriculture and industry - as well as heating in people's homes.
The WHO said the classification should act as a strong message to governments to take action.
The International Agency for Research on Cancer (IARC), a part of the WHO,...