"The air we breathe has become polluted with a mixture of cancer-causing substances," Dr. Kurt Straif, head of the IARC Monographs Section, said in a statement.
"We now know that outdoor air pollution is not only a major risk to health in general, but also a leading environmental cause of cancer deaths."
After thoroughly reviewing the latest available scientific literature -- a review of more than 1,000 scientific papers from studies on five continents -- the world's leading experts convened by the IARC Monographs Program concluded there is sufficient evidence that exposure to outdoor air exposure causes lung cancer and increases the risk of bladder cancer.
Particulate matter, a major component of outdoor air pollution, was evaluated separately and was also classified as carcinogenic to humans, Straif said.
The IARC evaluation showed an increasing risk of lung cancer with increasing levels of exposure to particulate matter and air pollution.
Air pollution is already known to increase risks for a wide range of diseases, such as respiratory and heart diseases. Studies indicated in recent years exposure levels have increased significantly in some parts of the world, particularly in rapidly industrializing countries with large populations, Straif said.
A summary is scheduled to be published online in The Lancet Oncology next Thursday.