Feel It in the Air: Pollution and Crime in Chicago

Chicago is notorious for its high crime rates. As noted by the University of Chicago’s Crime Lab, risk factors associated with crime include gender, age, race, economic status, exposure to violence, and community instability. A recent study ventures beyond individual and community characteristics to investigate how environmental factors may also affect crime. The study identifies a significant relationship between air pollution and criminal behavior. The researchers estimate that Chicago incurs $1.8 million in annual crime-related costs—a level that more than justifies further evaluation.

Using Chicago Police Department data on over two million crimes reported from 2001 to 2012, researchers Evan Herrnstadt and Erich Muehlegger evaluated pollution intensity at the time of reported crimes, while also considering the direction and power of winds blowing from nearby interstates. The researchers looked at the principal air-quality pollutants from vehicles, including carbon monoxide and nitrogen oxide.

This research provides the first quasi-experimental evidence that air pollution has a quantifiable impact on violent criminal activity. Results indicate that communities exposed to higher levels of air pollution experience a 2.2 percent increase in violent crime rates on average. The impact of air pollution on crime was found to be weaker on days when air pollution levels were lower.

The authors’ analysis finds that the increase in crimes committed comes from violent crime, as opposed to property crime, highlighting the relationship between pollution and aggressive behavior. Incidents of aggravated battery (where bodily injury is sustained) were more common during periods of pollution-induced crime. However, aggravated assaults (in which no bodily injury is sustained) decreased during these same periods. The researchers suppose that pollution causes a net increase in violent crime, but also results in marginal aggravated assaults that escalate into aggravated battery assaults. This relationship between pollution and aggression is consistent with contemporary research on the impact of air pollution on human behavior in general.

In medicine and economics, noted harms of pollution include adverse effects on child and adult health, a reduction in productivity and labor market participation, and cognitive impairment leading to lower test scores and avoidance behavior. From a physiological perspective, Herrnstadt and Muehlegger explain how air pollution can trigger inflammation in the central nervous system, which is also linked to aggression, impulsivity, and depression. In addition, the discomfort associated with air pollution itself can lead to pain and antisocial behavior, which can induce aggression.

In the study, researchers controlled for factors such as temperature and economic activity, allowing them to isolate air pollution as a contributing variable. It is interesting to note, however, that, during the spring and summer months, the impact of pollution increases crime rates to between six and eight percent, while the impact is near zero during the winter.

Pollution seems to have a greater influence on criminal activity during warmer months, relative to the coldest time of the year. The paper points to differences in vehicle emissions in cold and warm weather as a potential explanation behind this phenomenon and concludes that nitrogen oxide emissions (which are often higher during warm months) may be the primary pollutant influencing violent crime. In Chicago, a city known for its brutal winters and beautiful summers, a surge in crime during the summer is unsurprising. A greater number of people outside during warmer months could easily translate into a larger pool of motivated offenders and suitable targets.

Incidents of violent crime cost the US several hundreds of billions of dollars per year. This includes medical expenses, cash losses, property theft or damage, lost earnings due to injury, criminal justice costs, and career costs. This study extrapolates data from Chicago to forecast an incremental $100-$200 million in annual costs related to pollution-induced crime across America (excluding the enormous costs associated with homicides and loss of life). These costs are comparable in magnitude to other commonly studied effects of traffic pollution on health, such as pre-term birth.

Addressing crime in large cities is certainly a long-term task. Understanding the factors that lead to risky and aggressive behavior is essential to any strategy that seeks to alleviate patterns of crime. Although this study focuses solely on air pollution from motor vehicles, communities adjacent to oil refineries, chemical plants, and coal-fired power plants are also susceptible to higher levels of pollution. These areas also tend to be more affordable and have more low-income residents. Managing the adverse effects of pollution appears to be one more hurdle that individuals living in disadvantaged communities navigate on a daily basis.

Article Source: Herrnstadt, Evan, and Erich Muehlegger, “Air Pollution and Criminal Activity: Evidence from Chicago Microdata,” National Bureau of Economic Research, December 2015.

Featured Photo: cc/(Eric Schmuttenmaer)