Researchers with Harvard University and the University of California, Davis published a study claiming to have “the first quasi-experimental evidence that air pollution causally affects criminal activity." For example, the researchers claim “ violent crime is 2.2 percent higher” on the side of the Chicago’s I-290 freeway that’s downwind of air pollution.
On days when a given neighborhood was downwind from a major freeway, and exposed to heightened tailpipe pollution, the researchers—Evan Herrnstadt and Erich Muehlegger—found that violent crime in that neighborhood rose 2.2 percent. Property crimes were uncorrelated with exhaust levels. Their findings were published in a paper published by the National Bureau of Economic Research.
The conclusions are based on 12 years of crime data from the Chicago Police Department. The dataset encompassed more than 2 million “serious” crimes, each tagged with location data; the researchers paired this information with meteorological data on local wind patterns, to find out when an area was downwind or upwind from the freeway.
According to the Washington Post, it isn’t clear precisely how the pollution would be affecting people in a way that promotes criminal behavior—especially violent criminal behavior—but the authors list a number of possibilities, including cognitive impairment and just greater irritation.
“We think the mechanism here is that you’re exposed to more pollution, either it’s an irritant, or it affects your impulse control in some other way, and basically results in you crossing lines that you wouldn’t otherwise cross,” said Herrnstadt. That’s why, he said, the data suggest more assault cases escalating into cases of battery in the presence of pollution.
The result is actually not so surprising when considered in the context of prior research, said Josh Graff Zivin, an economist at the University of California-San Diego who commented on the paper at the Post’s request. “There is a body of epidemiologic health literature that shows that pollution at high levels can impair judgement, can increase aggression, can impair cognition,” said Zivin.
The Post noted that a body of prior research has tied another environmental factor — warmer temperatures — to crime and violence, and there has also been research suggesting that lead pollution drove a large amount of criminal activity that, once lead was phased out of gasoline, dropped off. There is also a small but growing body of research suggesting that poor indoor air quality can have significant cognitive effects.
What’s more surprising about the study, said Zivin, is that “if you think the crime that they see in their paper, violent crimes, if you think that those are in part about impulse control, then this is really novel. As far as I know, we don’t really have evidence that pollution can lead to increased impulsivity.”