Fine-particulate air pollution is strongly associated with DNA changes that drive lung cancer in people who have never smoked, according to the largest whole-genome study yet conducted on the disease. The National Institutes of Health and the University of California, San Diego, sequenced tumours from 871 never-smokers in 28 regions and reported their findings in Nature on 2 July. Researchers found that patients living in areas with higher levels of PM2.5 carried 3.9 times more smoking-related mutational signatures and 76 percent more aging-related signatures in their tumours than peers from cleaner environments. The polluted-area tumours also showed frequent alterations in the TP53 gene and signs of accelerated telomere shortening, whereas exposure to second-hand smoke produced far fewer cancer-driving mutations. Never-smokers already account for as much as a quarter of global lung-cancer cases, a proportion that is rising even as tobacco use declines. The authors say their work clarifies a genomic mechanism behind that trend and could guide prevention strategies focused on air-quality regulation while they expand the research to other environmental risks.