Long-term exposure to particulate air pollution boosts the risk of lung cancer, even at concentrations below the legal maximum, says a European study published on Wednesday.
A separate report says short-term surges in these particles or other gas pollutants in the air also increases the risk of heart failure.
European epidemiologists say they had found an unmistakeable link between lung cancer and air pollution by particulate matter.
The evidence comes from 17 high-quality investigations carried out among 312,000 people in nine European countries, according to the paper in The Lancet Oncology.
These earlier studies, which had already been published, were based on records of the health and lifestyle of 2095 people who died from lung cancer during an average 13-year monitoring period.
The team sourced environmental data around the individuals' home addresses, then calculated their exposure to levels of particulate matter - the gritty residual pollution from fossil-fuel-burning power stations, cars and factories.
Particulate matter falls into two categories: PM2.5, meaning particles measuring no more than 2.5 micrometres, 30 times smaller than a human hair, and the slightly coarser variant, PM10.
EU air quality standards limit PM10 exposure to a yearly average of 40 microgrammes per cubic metre, and PM2.5 exposure to 25 microgrammes per cubic metre.
The UN's World Health Organisation has guidelines recommending that annual exposure be limited to 20 microgrammes per cubic metre for PM10 and 10 microgrammes per cubic metre for PM2.5
Unexpectedly, the new study found a cancer risk at every level, and confirmed that the higher the level, the greater the risk.
The results took account of smoking, diet and occupation - which can skew the risk picture.
''We found no threshold below which there was no risk,'' said Ole Raaschou-Nielsen from the Danish Cancer Society Research Centre in Copenhagen. ''The more the worse, the less the better.''
Every increase of five microgrammes per cubic metre of PM2.5 drove the risk of lung cancer up by 18 per cent.
Every increase of 10 microgrammes per cubic metre of PM10 boosted risk by 22 per cent, including for adenocarcinoma, a type of lung cancer associated with non-smokers.
AFP
