In the future, police and crime prevention units may begin to monitor the levels of pollution in their cities and deploy resources to areas where the pollution is the most severe in a given day.
This may sound like a plot of a science fiction movie, but recent findings suggest that this may well be a worthwhile practice.
Why? Emerging studies show that air pollution is related to impaired judgment, mental health problems, poorer performance in school and most worryingly perhaps higher levels of crime.
These findings are all the more alarming, given that more than half of the world's population now live in urban environments – and more of us are traveling in congested areas than ever before.
Air pollution kills an estimated seven million people a year. Staggeringly, the World Health Organization says nine out of 1
BBC Future considers the evidence.
Watch our animated version on BBC Reel: How dirty air is polluting our minds
It was in 2011 that Sefi Roth, a researcher at the London School of Economics, was pondering the many effects of air pollution. He was well aware of the negative outcomes on health, increased hospital admissions and also mortality.
To begin with, he conducted a study examining whether air pollution had an effect on cognitive performance.
Roth and his team looked at students taking Exams are different days – and also measured how much pollution was in the air on those given days. All the other variables remained the same: The exams were taken by students of similar levels of education in the same place, but over several days.
He found that the variation in average results was staggeringly different. The most polluted days correlated with the worst test scores. On days where the air quality was cleanest, students performed better.
"We could see a clear decline [of performance] in days that were more highly polluted," says Roth. "Even a few days before and after, we found no effect – it's really just in the day of the exam that the test score was significantly reduced."
To determine long-term effects, Roth followed up to see what impact this had eight to 10 years later. Those who performed the worst at the most polluted days were more likely to end up in a lower-ranked university and also earn less because the exam was so important for future education. "Even if it's a short-term effect of air pollution, if it occurs in a critical phase of life, it can really have a long-term effect," he says . In 2016, another research backed up Roth's initial findings that pollution can result in reduced productivity.
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These insights are what led to Roth's most recent work. In 2018, research his team analyzed two years of crime data from over 600 London's electoral wards and found that more petty crimes occurred in the most polluted days in both rich and poor areas.
It is important to note that this finding is purely correlational – but Roth has reason to believe that there is a causal link.
Where the cloud of pollution travels, crime increases
His team also compared very specific areas over time, as well as the following levels of pollution over time . A cloud of polluted air, after all, can move around depending on which direction the wind blows. This takes pollution into different parts of the city, at random, to both richer and poorer areas. "We have just found out that wherever it goes crime rates increases," he explains.
Importantly, even moderate pollution has made a difference. "We find that these large effects on crime are present at levels which are well below current regulatory standards." In other words, levels that the US Environmental Protection Agency classifies as "good" were still strongly linked with higher crime rates.
While Roth's data did not find a strong effect on the more serious crimes of murder and rape, another study from 2018 has shown a possible link. The research, led by Jackson Lu of MIT, has been examining nine years of data covering almost the entire US in over 9,000 cities. It found that "air pollution predicted six major categories of crime", including manslaughter, rape, robbery, theft of cars and assault. The highest pollution rates in the cities also had the highest crime rates.
Further evidence comes from the study of "delinquent behaviour" (including cheating), which is a major source of increased crime. , truancy, stealing, vandalism and substance abuse) in over 682 adolescents. Diana Younan, of the University of Southern California, and colleagues specifically looked at PM2.5 – tiny particles 30 times smaller than the width of human hair – and considered the cumulative effect of exposure to these pollutants over a period of 12 years. Once again, the bad behavior was significantly more likely in areas with higher pollution.
To verify the link could not be simply explained solely by socioeconomic status, Younan's team also accounted for parental education, poverty, the quality of their neighborhoods,
Younan says that her findings are particularly worrying as we know that how a person behaves during adolescence is a strong predictor of how they will. behave as an adult. Delinquent individuals are more likely to perform worse at school, experiencing later unemployment and are more prone to substance abuse. This means that intervention in an early age should be a priority.
Lu, for example, has shown that the mere thought of pollution can affect our psychology through its negative associations.
Naturally, the researchers were unable to physically expose participants with pollution, so they took the next best (ethically approved) step. They showed both US and Indian participants photos of an extremely polluted city and asked them to imagine themselves living there. "We made them psychologically experience the effects of pollution," Lu explains. "… then asked them to really imagine living in this city, and how they feel and how their life would live in this environment, to make them psychologically experience air pollution versus clean environment."
He found that the participant's anxiety, and they became more self-focused – two responses that could increase aggressive and irresponsible behaviors. "As a self-defense mechanism, we all know that when we are anxious we are more likely to punch someone in the face than when we are calm," says Lu. "So, by elevating peoples' anxiety, air pollution can have a detrimental effect on behavior."
When we are anxious we are more likely to punch someone in the face than when we are calm
Across further experiments, the team showed that participants in "polluted" conditions were more likely to cheat on several tasks and overrate their performance in order to get rewards.
This research is just the beginning, and there could be many reasons for these effects besides increased anxiety and self-focus that Lu describes – including physiological changes to the brain. For example, when you breathe in polluted air, it affects the amount of oxygen you have in your body at a given moment – and that, in turn, can result in reduced "good air" going to your brain.
It is also clear that exposure to various pollutants can cause a brain stomach and can damage the brain structure and neural connections. "So what could be happening is that these air pollutants are damaging the pre-frontal lobe," says Younan. This is the very area important for controlling our impulses, our executive function and self-control.
Besides elevating crime, that could also lead to a serious deterioration in mental health. A March 2019 study even showed that teenagers exposed to toxic, polluted air are at a higher risk of psychotic episodes such as hearing voices or paranoia. Lead researcher Joanne Newbury, from King's College in London, says she can not yet claim that her results are causal, but the findings are in line with other studies suggesting a link between air pollution and mental health. "It adds to evidence linking air pollution to physical health problems and air pollution linked to dementia. If it's bad for the body, it's to be expected that it's bad for the brain, "she says.
Those in the field say that now there needs to be more awareness about the impact of pollution, along with well-established effect on our health. "We need more studies showing the same thing in other populations and age groups," says Younan.
Fortunately, we have some control over how much pollution we are exposed to day to day. We can be proactive and look up the air quality around us in a given day. Monitors highlight the days it is most dangerous, and when it is lowest. "If it's dangerous I would not suggest going for a run outside or do your work indoors," says Younan.
While many countries are waiting for stricter legislation or government intervention to reduce pollution, some places have taken positive steps. Take California, where regulation has resulted in less pollution, and interestingly, also less crime. Though promising, Younan stresses that we do not yet know if this is a coincidence or not. Meanwhile in London, from April 8, 2019, there will be a "ultra low emission zone" that has stricter emission standards with an additional £ 12.50 ($ 16.30) daily charge for "most vehicle types" on top of the existing £ 11.50 overcharge charge. A lot of greener buses are also being phased in under the cleaner air for London initiative.
"We are doing a fairly good job in cutting pollution in many countries, but we should do more," says Roth. "It's not necessarily just government. But we also need to be more aware of that and make informed decisions about what we do. " Roth remains hopeful that rising pollution is something that we are in our control to solve, but until we do, we need to make people more aware of these issues.
If we all begin to monitor pollution levels ourselves, then we might begin to make it a habit to avoid certain activities, such as outdoor sports, or even commuting on the most polluted days. Our bodies, brains, and behaviours will benefit.
Melissa Hogenboom is editor of the BBC Reel. Her film on the same topic can be seen here, she is @melissasuzanneh on twitter.