Lung cancer cases are on the rise in non-smokers around the world, and air pollution could be an insidious, contributing factor.

A genome study has now found that outdoor smog and soot are strongly associated with DNA mutations related to lung cancer – including known drivers seen in smokers, and new ones unique to non-smokers.

The more pollution someone was exposed to, the more mutations scientists found in their lung tumors.

The findings don’t mean that air pollution is directly causing lung cancer, but they do contribute to evidence suggesting that possibility.