When there is a question, it can be helpful to look at the science behind the theory. Studies have shown that exposure to air pollution can cause "oxidative stress," that is, damage to the cells of the body caused by oxidation. This in turn can lead to the development of cancer.
Studies in the United States, Europe, and Asia have suggested that air pollution from traffic and the combustion of coal, diesel fuel, and wood, has a modest association with lung cancer risk. In a 2009 U.S. study, it was estimated that 5% of male lung cancers and 3% of lung cancers in women between 1970 and 1994 were related to air pollution. One study looking at urban air pollution in Europe suggests that the risk may be higher, with up to 10.7% of lung cancer cases considered related to exposure to air pollution.