In an analysis of data from nearly 700 children, Younan and her team found that kids in Los Angeles who were exposed to more air pollution over the course of adolescence were more likely to engage in delinquent behavior.

Read the article for details, but it seems pretty thorough.

Younan specifically looked at the pollution from particulate matter 2.5, tiny particles that are 30 times smaller than a human hair. “It’s not smog that people can see,” she says. “But if they can’t see it, it’s bad.” This type of pollution primarily comes from cars and traffic, Younan says.