India pollution
A boy wears a mask as he stands at the India Gate monument whilst heavy smog covers New Delhi, India. Sajjad Hussain/ AFP

There is a link between high levels of air pollution and increased delinquency or bad behaviour among young people, according to a new study conducted by researchers from the University of Southern California.

In polluted areas, the air you breathe contains tiny particles called particulate matter 2.5 (PM2.5), which, despite being 30 times smaller than a strand of hair, are extremely harmful to health and may even affect our behaviours. So says Diana Younan, lead author of the study.

"These tiny, toxic particles creep into your body, affecting your lungs and your heart," said Younan. "And studies are beginning to show exposure to various air pollutants also causes inflammation in the brain. PM2.5 is particularly harmful to developing brains because it can damage brain structure and neural networks and, as our study suggests, influence adolescent behaviours."

The study, published in the Journal of Abnormal Psychology, examined the effects of ambient air pollution on 682 young people between the ages of 9 and 18 in Greater Los Angeles. Over a period of nine years, parents completed surveys, noting whether their children had engaged in rule-breaking behaviours such as lying, cheating, truancy, stealing, vandalism, arson and substance abuse, among others.

The data was adjusted for gender, ethnicity, socioeconomic status and neighbourhood quality.

Researchers then compared each participant's address to estimated pollution levels outside each home. Around 75% of those who took part in the study lived in areas which breached US federal recommended levels of 12 micrograms per cubic metre, with some people living in neighbourhoods which had nearly double this amount.

Researchers have long-speculated whether higher levels of air pollution lead to increased criminal activity. The study notes that PM2.5 concentrations have fallen in Southern California just as crime rates suffered a similar decline. Future studies need to be conducted to determine whether this is a coincidence or if tighter air regulation has actually contributed to falling crime rates.

"Poor people, unfortunately, are more likely to live in urban areas in less than ideal neighbourhoods," Younan said. "Many affordable housing developments are built near freeways. Living so close to freeways causes health problems such as asthma and, perhaps, alters teenagers' brain structures so that they are more likely to engage in delinquent behaviour."

The bad behaviours linked with higher pollution levels were magnified when children did not have healthy relationships with their parents or lived in homes where the parents were stressed, the authors suggest.

"A bad parent-child relationship causes a stressful family environment, and if this goes on for too long, the teenager could be in a chronic state of stress," Younan said. "This could wreak havoc on the body, making teens more vulnerable to the effects of exposure to small particles."

Younan advises that if you live in an area with high air pollution, avoid going outside for extended periods and keep windows closed when PM2.5 levels are high.