FILE - This is a May 7, 2013 file photo of a foreign tourist wearing a mask walks in front of Tiananmen Gate on a polluted day in Beijing, China. What many commuters choking on smog have long suspected has finally been scientifically validated: air pollution causes lung cancer. The International Agency for Research on Cancer declared on Thursday that air pollution is a carcinogen, alongside known dangers such as asbestos, tobacco and ultraviolet radiation. (AP Photo/Alexander F. Yuan, File)LONDON (AP) — What many commuters choking on smog have long suspected has eventually been scientifically validated: air pollution causes lung cancer.