On Thursday, the World Health Organization officially added air pollution to the list of leading causes of cancer worldwide.
"We consider [air pollution] to be the most important environmental carcinogen, more so than passive smoking," said Kurt Straif, head of the International Agency for Research on Cancer department that detects cancer-causing substances.
Unfortunately, the agency had few recommendations for how we should indiviually deal with the new classification. "When I walk on a street where there's heavy pollution from diesel exhaust," Straif told NBC News, "I try to go a bit further away. So that's something you can do."