American researchers have established a possible link between air pollution and violent crime with a study showing that exposure to higher levels of particulate matter and ozone corresponded to a rise in incidents such as assaults.
The study uncovers a new, immediate risk factor associated with a problem that has already been linked to long-term harms such as reduced life expectancy, and indicates pollution may be triggering a more aggravated response among people.
The study is centered on an analysis of crime and environment data from 397 counties, or 28.3% of the population in the United States between 2006 and 2013, by a team of researchers from Colorado State University and the University of Minnesota.
“The results suggest that changes in PM2.5 and ozone have significant acute effects on violent crimes with a particular emphasis on assaults. Assaults include physical attacks, which is likely indicative of impulsive and aggressive behavior,” said the report published in the Journal of Environmental Economics and Management on September 30.
A 10% increase in levels of PM2.5 – the most harmful of all commonly found aerosols – correlated with a 0.14% rise in assaults. Similarly, a 10% increase in ozone levels corresponded to a 0.3% spike in violent crimes.
The findings are based solely on the statistical relationship and does not go into the connection between pollution and its physiological triggers, but lead author and Colorado State University professor Jesse Burkhardt said there are several theories that could explain the findings.
“There are two competing hypotheses, in my mind. One is that pollution enters your bloodstream and affects the way your brain works – studies, for instance, have shown that those exposed to pollution fare poorly on tests…
“The other is that when you’re exposed to pollution, it hurts. If it triggers your allergies, your eyes are watering. If it triggers asthma, you face breathing difficulties. That would lead to aggravation,” said Bukhardt in a video call.
“Unfortunately, we can’t say which one is happening because it’s hard to show that with data that is essentially aggregate-level crimes in a day,” he added.
A behavioural expert agreed that environmental factors like pollution can lead to aggression. “There have been studies earlier that have linked triggers such as heat, noise, population density as triggers for aggressive behaviour, and now pollution can also be added in that list,” said Dr Samir Parikh, director, department of mental health and behavioral sciences, Fortis Healthcare.
“Even though there is no denying pollution can act as irritants, one needs to also consider other factors such as personality type, social environment etc,” he added.
Burkhardt said the study’s statistical model takes into account all other possible factors such as demographic and economic variations. “One of the big questions people will obviously ask is; wouldn’t a place that is urban have more crime but also have more pollution? Of course, so we controlled for that,” he said, explaining that this was done by looking at the findings through several alternative methods.
The professor cautioned that the effects in the findings may be seen as very small and policymakers are unlikely to consider the corresponding benefit in terms of reduced violent crimes as a strong enough reason to act. “But addressing pollution has to be seen as a cost-benefit analysis. Fewer people will die if pollution is reduced, and that’s the benefit. The costs would be that it is expensive to, say, change your entire fleet of public transport. So, on a scale, putting that extra cost will lead to a little more weight on the benefit side because that is when people won’t get sick,” Burkhardt said.
The report estimates that a 10% reduction in daily PM2.5 and ozone exposure could save United States about $1.4bn a year in costs such as those incurred by law enforcement and what is lost in productivity due to injuries.
