The Los Angeles and Century City skyline partially obscured through smog
Century City and downtown Los Angeles seen through smog. Lucy Nicholson/Reuters

A new study from the University of Southern California suggests a link between air pollution and adolescent delinquency.

We already know that invisible elements of our environment can harm us: Lead exposure can lower a child’s IQ, and air pollution kills more than 3 million people a year. Now, a study from the University of Southern California’s Keck School of Medicine suggests that air pollution may be having insidious effects on young people’s brains.

The study, published last week in the Journal of Abnormal Child Psychology, followed 682 children in greater Los Angeles for nine years from the age of nine to 18. It concluded that air pollution may increase delinquent behavior in adolescents.

From 2000 to 2014, researchers measured daily air pollution in Southern California. The pollution was measured as particulate matter or PM2.5, which refers to the maximum diameter, 2.5 microns, of the tiny particles measured. (As a point of comparison, a strand of hair is around 60 microns thick.) To assess delinquency, researchers asked parents to keep a child-behavior checklist, where they recorded behaviors such as lying, stealing, and substance abuse.

While parsing the study’s air quality and child behavior data, researchers saw that air pollution estimates were higher in neighborhoods near freeways and with less foliage, and found that delinquent behavior was more prevalent among boys, African Americans, adolescents from lower socioeconomic backgrounds, and those who lived in neighborhoods with limited green space. The study also noted that the effects of air pollution on delinquency were worsened by poor parent-child relationships and social stress.

In order to adjust for the different living and environmental factors of participants, researchers gave questionnaires to parents that recorded the gender, ethnicity, socioeconomic status, and residential characteristics of the children who were participating.

“We saw that [air pollution] was still having an adverse affect, even after for controlling for all these variables,” said Diana Younan, the study’s lead author. Younan said she wasn’t exactly surprised by the study’s findings. “Over the past 20 years, air pollution studies have been coming out and showing that it can affect the brain,” she said. “But looking at specific behaviors, [like] substance abuse and mental health, is still new.”

The new study points out that both PM2.5 concentrations and crime rates have been falling in Southern California, and suggests conducting more research into whether the former may have been a contributing factor for the latter. But the effects of existing pollution are detrimental, particularly for minority communities. According to the Los Angeles Times, the City of Los Angeles signed off on 3,000 housing units near freeways in 2016, even though people who live near traffic pollution suffer from a spate of health problems including higher rates of hearth attacks and lung cancer. And research has shown that communities of color tend to be disproportionately affected by air pollution.

Younan said that she would be careful about claiming outright that air pollution causes delinquency. “I wouldn’t use the word ‘causation,’” she said. “But we know the exposure occurred before the outcome. We can say [the study] provided evidence that there’s a strong association between the two.”

Delinquency can’t just be written off as youthful misbehaving. Especially from the ages of 12 to 16, it is a strong predictor of future criminal convictions. (A 2015 paper from the National Bureau of Economic Research posited that car pollution had a measurable effect on Chicago’s criminal activity.) But it is only one of the side effects of air pollution. Younan’s past work has looked at the link between air pollution and obesity, and how air pollution may cause dementia in older women.

Younan hopes that more researchers will take up the issue, so that the evidence of air pollution’s effects on adolescents will become impossible for cities to ignore. “For policy to change, there [have] to be a lot of studies coming out to show this,” she said.

Decreasing air pollution is no easy feat: Its causes are rooted in many aspects of city life. Lawmakers would have to tackle reforms in everything from transportation to construction to industry to curtail it significantly. According to Younan, one of the hardest parts of enacting pollution reform is getting the city and its sectors even to address it.

“Air pollution is dangerous for many organs,” she said. “Not just the lungs, or the heart, but the brain.”

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