Apart from harming people’s health and the environment, air pollution seems to be linked with criminal activity.

According to findings published in Psychological Science, a journal of the Association for Psychological Science, exposure to air pollution predicts unethical behavior, including cheating and criminal activity.

Adam D. Galinsky and Jackson G. Lu from Columbia University, along with their colleagues, Harvard’s Francesca Gino and University of Michigan’s Julia J. Lee, published a research article titled “Polluted Morality: Air Pollution Predicts Criminal Activity and Unethical Behavior.”

This research is, authors wrote, a response to former president Barrack Obama’s Executive Order issued in 2015, which advocated the use of behavioral science insights to “better serve the people.” The researchers’ aim was to investigate the ethical costs, as they put it, of air pollution, and “thus provide another compelling reason for policymakers to combat air pollution.”

Their findings, a combination of archival and experimental studies, suggest that exposure to air pollution predicts crime.

“Air pollution is a serious problem that affects billions of people across the globe. According to the Environmental Protection Agency (EPA), about 142 million Americans still reside in counties with dangerously polluted air,” researchers wrote, adding that “air pollution heightens anxiety, which in turn increases unethical behavior.”

Previous studies have indicated that exposure to polluted air elevates anxiety levels. For example, in 2015, Reuters published a media summary of a Johns Hopkins University study, which suggested that higher exposure to fine air pollution particles meant higher levels of anxiety. Although the study’s lead author, Melinda C. Power, told Reuters at the time that “air pollution may be related to mental health,” this was an observational study. Further research was needed.

Researchers lead by Jackson G. Lu from Columbia University examined air pollution data, maintained by the Environmental Protection Agency, and crime data, maintained by the FBI, in over 9,000 U.S. cities over a 9-year period. Cities with higher levels of pollution had higher levels of crime. Even after the researchers included factors such as total population, unemployment rate, poverty rate, gender, and race distribution, the link between criminality and air pollution held water.

To further verify their claims and establish a causal link between unethical behavior and air pollution, the researchers conducted various psychological experiments. In one of the experiments, the participants were shown photographs of polluted scenes and clean scenes. They were then asked to imagine living in the location.

After this, the participants were subjected to an unethical-behavior measure. They were shown a set of cue words and had to identify another word, linked with each of the cue words. However, due to a “computer glitch,” the correct answer popped up if the participants hovered their mouse, which the researchers asked them not to do.

This is how the researchers described the unethical behavior measure.

“Participants completed a supposedly unrelated task – the Remote Associates Test – which presents three cue words and asks the participant to identify a fourth word associated with each of the three words (e.g., sore, shoulder, sweat – cold). Participants attempted five RATs in a fixed order after a practice trial. For each correctly answered RAT, participants received a bonus of $0.50. We informed participants that the program had a glitch that would allow the answer for each RAT to appear in a box below the three cue words if they hovered their mouse over the box.”

The results showed that even imagining exposure to air pollution leads to unethical behavior; participants who thought about polluted areas cheated more often than those who did not.

In another experiment, participants were shown polluted and clean scenes of the exact same location and then asked to write an essay. Participants who wrote about living in polluted areas expressed more anxiety in their writing.

These findings, researchers assert, suggest that exposure to air pollution, even if only mental, is linked with increased levels of anxiety, and increased levels of anxiety are linked with transgressive behavior.

Lu and colleagues acknowledge that anxiety is not the only link between air pollution and unethical behavior, but the lead author concluded that these findings “suggest that air pollution not only corrupts people’s health, but also can contaminate their morality.”

“A less polluted environment is not only a healthier one, but also a safer one,” authors wrote.

The United States Environmental Protection Agency recently updated a section on their official website, arguing that the air in America has gotten dramatically cleaner, but the agency also acknowledged that air pollution in the United States continues to harm people’s health and the environment. Likewise, a study published in the New England Journal of Medicine found a strong correlation between mortality and exposure to air pollution.