How Air Pollution Acts as a Force Multiplier for Aggressive Behavior, and What Can Be Done About it

By now, we are well aware of the catastrophic effects of greenhouse gas emissions and corrupt industrial practices. We are pumping pollutants into our atmosphere at least 10 times the rates at which humans did 250 million years ago when the largest extinction event in Earth’s history nearly wiped out all life on Earth. Low-altitude pollutants like carbon monoxide, nitrogen dioxide, sulfur dioxide, and lead have been proven to make asthma more severe and common, cause lung cancer, and constitute a leading factor in cardiopulmonary deaths. Air pollution now also accounts for the leading cause of death in India.

However, one victim of air pollution has not received as much attention: our cognition. The mental health effects of pollution have been demonstrated both chemically and epidemiologically. Several studies have observed disruptions to blood flow, neural generation, and neural networking in otherwise clinically healthy humans and animals who were chronically exposed to air pollutants and particulate matter (PM). Epidemiologically, even exposure while a fetus has been shown to increase the risk of developing a wide range of mental disorders from Autism Spectrum Disorder to Schizophrenia. While surely not the only factor in our modern mental health crises and crime waves, scientific literature now confirms that pollution is directly interfering with our neuro-chemical regulation systems, inhibiting our ability to regulate our thoughts, emotions, and behavior. Even more concerningly, these wide-ranging neurological effects can lead to certain negative behaviors, such as violence.

The Anatomy of Aggression: How Pollution Increases violent tendencies

Fine particulate matter, or those particles emitted with a diameter of less than 2.5 microns (PM2.5), enter the bloodstream through our breathing and cause systemic inflammation of vital organs, including the brain. Inflammation of the brain impairs cognitive functioning, which in turn leads to more impulsive decision-making and more instances of aggression. One study in the Journal of Environmental Economics finds that an increase of one microgram per cubic meter (µg/m3) of PM2.5 increases violent crimes by 0.53% across the United States. This equates to an extra 327 violent crimes across the United States every month or more than 4,000 each year. Bolstering the study’s findings, there was little effect on other, non-violent crimes like fraud, which suggests that particularly impulsive crimes such as aggravated assault are most strongly affected by high concentrations of fine particulate matter.

Moreover, a team from Columbia and Harvard also found that pollution levels lead to more activity in a variety of criminal categories — even when controlling for economic variables like income, unemployment levels, and industry type; demographics such as gender and education level; and even law enforcement presence. This study also points out that the impact of social-level multipliers such as the “broken-window” effect will make the cognitive effects of pollution cyclical. “The broken window” effect refers to the phenomenon in which individuals are more likely to treat an environment and the people within it with less respect if they deem it to be neglected. Just as you may be more likely to litter on a street already containing litter, individuals may be less likely to treat an environment with respect if they believe it to be already in a state of disrepair. Such phenomena will make the persistent presence of pollutants endemic and continue to increase anti-social and aggressive tendencies unless our local and federal governments take action.

Mitigation: Small-scale, Realistic, and Locally driven

On a more positive note, unlike the more transformational solutions to reducing the impacts of climate change, mitigating the cognitive effects of air pollution is comparatively simple. Direct-impact air pollution is, perhaps, one of the only areas of the environmental movement which has seen real success. Incentives to drive cleaner and fewer cars will suffice to address the worst of the impact of pollution on impulsive behaviors and violence.

The most immediate and tangible policy we can deploy is to reduce the emissions of everyday automobiles. Reducing automobile emissions does not mean switching to expensive, all-electric vehicles, however – just to newer, less gas-hungry models. As a study of the Toronto Metro Area traffic demonstrates, 75% of harmful pollutants come from just over 25% of vehicles or, more specifically, older, more fuel-intensive cars. A 2020 OECD report substantiates this claim, finding that as emissions standards increase and more electric cars are adopted, particulate matter from vehicle brakes, wearing down of tires, and road surface abrasion will overtake fuel emissions as the leading source of vehicle particulate emissions within the next two decades. Incentive-based scrappage schemes would take these older, polluting vehicles off the roads and drive down particle levels.  

By reducing the use of such environmentally-taxing vehicles, these policies should aim to reduce urban pollution levels to the WHO’s target of 5µg/m3. Large North American cities have already managed to reduce pollution to around 8-12µg/m3 without scrapping a single car, and only 7% of Americans report owning an electric or hybrid car. Introducing scrappage incentive schemes will drive these particle levels down even further. Strict emission standards and scrappage incentives for older and less efficient vehicles are short-term and relatively less expensive than massive structural changes to a nation’s energy grid or replacing entire fueling infrastructure, as London’s vehicle scrappage scheme has shown. Consumers will benefit from a discount on a new, safer, more fuel-efficient car. State governments will also save money by having less physical pollution to clean up and fewer violent criminals to arrest, try, and imprison. Hospitals will save on having to treat fewer patients for physical and mental problems, and fewer victims of violent crime to treat in the ER. The benefits to early action increase disproportionately, while so too do the costs of inaction.

The adoption of cleaner vehicles is not the only solution. Sources of pollution other than exhaust fumes require that cities pursue mass transit with greater tenacity. Knowing that particulate matter from the breaks and tires of each car can increase violence as well should incentivize city governments, even more, to invest in mass transit and alternative transport access. The number of tires hitting the roads every day incurs huge social and economic costs. Environmentalists have always recommended increased buses, light rail, and cycle lanes; this cross-cutting of violent crime with this issue is an excellent way to refocus the movement on human costs of pollution, rather than high-minded idealism. In sum, emerging research demonstrates that pollution strikes at the very core of human security: our ability to think about and reason with the world around us. Without serious action, those humans able to cope with the physical and economic effects of climate change will find themselves more anxious, erratic, and prone to anger and violence. Cheap, local, and effective mitigation measures already exist for local and federal governments to implement. By transitioning to both cleaner vehicles and public transportation systems, we can mitigate the most severe cognitive effects of air pollution and prepare ourselves to navigate the disruption of climate change.

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