We all know air pollution is bad for our health. But it can also harm us in other ways. Scientists have found that air pollution may lead to more violent crime (暴力犯罪). According to a study of 86 million people in the US, the worse the air pollution was, the more violent crime there was. Scientists think particles (微粒) and toxic gas (毒气) in air may affect people’s brains. This might make them more violent.