New research published in Developmental cognitive neuroscience provides evidence that breathing in high levels of neighborhood air pollution tends to slow normal brain and mental development in teenagers. Scientists found that children living in areas with high levels of particulate matter and surface ozone had less maturation in brain structure and problem-solving skills over a two-year period than children living in cleaner environments.
The transition from childhood to early adolescence is a critical stage for structural brain development and mental growth. During this period, the brain undergoes physical changes and network reorganization that allow young people to maintain focus, process information, and regulate behavior. Scientists conducted this study to understand how certain environmental factors disrupt these natural developmental processes.
“Environmental influences can shape many aspects of brain and cognitive development,” said Omid Kardan, assistant professor of psychiatry at the University of Michigan and lead author of the study. “I am particularly interested in distinguishing between social and physical environmental exposures, as they may offer different opportunities and scales for potential interventions. Air pollution is a particularly interesting physical environmental factor, as studies involving animal models have shown multiple pathways that can influence the brain and its development.”
Previous studies on air pollution and young brains have yielded mixed results. Some past studies have suggested that pollution affects brain thickness, while others have found no such association. The authors noted that these discrepancies may have arisen because early studies often did not correlate brain imaging data with actual behavioral tests such as memory or attention.
Additionally, previous studies have typically assessed children’s brain networks using templates based entirely on adult brains. Preteen brains are still transitioning from childhood patterns to adult patterns, so using an adult template can miss subtle developmental stages. To address these gaps, researchers designed a study that combined multiple types of brain scans with a battery of cognitive ability tests.
To collect the data, scientists used information from cognitive development studies of the adolescent brain. This is a large-scale, ongoing project that tracks the biological and behavioral development of thousands of young people across the United States. “We would like to thank the Adolescent Brain Cognitive Development (ABCD) study, whose large sample size and longitudinal neuroimaging and behavioral assessments made this type of investigation possible,” Cardan said.
The scientists focused on 3,645 participants who completed brain scans and cognitive tests when they were nine or 10 years old, and then again two years later when they were 11 or 12 years old. The researchers considered three specific measures to track neurocognitive maturation during this period. First, they measured changes in the thickness of the cerebral cortex, the outer layer of the brain’s gray matter.
As children grow into teenagers, this outer layer naturally thins through a healthy process called synaptic pruning. During synaptic pruning, the brain eliminates unused connections to become more specialized and efficient. The scientists then mapped how the young people’s brain networks communicated with each other during rest.
They calculated a maturation score by comparing each child’s functional brain connectivity to both the typical infant brain and the typical young adult brain. Over time, the mature brain should look increasingly different from the infantile template and become more similar to the adult template. Third, the researchers measured overall cognitive performance using a combination of standardized computer tasks.
These tasks tested a wide range of mental abilities, including sustained attention, working memory, processing speed, and reading recognition. They also tested inhibitory control, the mental ability to ignore distractions, control impulses, and stay focused on a specific goal. The researchers then categorized young people based on the average air quality in their home neighborhoods.
They used the official standards for unhealthy air set by the U.S. Environmental Protection Agency. Particulate matter consists of small, inhalable particles, often produced by car exhaust, wildfires, and power plants. Ground-level ozone is an invisible gas produced when pollutants chemically react with sunlight.
The researchers created two separate comparisons to study each pollutant without overlapping effects. In the initial analysis, they identified 348 young people who were exposed to unhealthy levels of particulate matter. They matched these participants with 279 peers living in low-pollution areas.
In the second analysis, researchers compared 355 youth exposed to high-altitude surface ozone to 324 youth in low-ozone environments. In both groups, the scientists paired high-pollution youth with low-pollution youth based on household income, parental education, race, biological sex, and age. This matching process helped confirm that differences in brain development were related to air quality, rather than socioeconomic status or systemic inequality.
“We used a powerful method to isolate the association between exposure to air pollutants (rather than other variables such as socioeconomic factors) and neurological and cognitive development,” Cardan told PsyPost. “Our results showed that young people (9 to 12 years old) living in highly polluted areas had lower than expected neurological and cognitive growth compared to demographically matched young people living in low polluted areas.”
Interestingly, the demographic profiles of the two contaminated groups were markedly different. “Youth exposed to high concentrations of fine particulate matter (PM2.5) and youth exposed to high concentrations of ozone (O3) pollutants had lower and higher socio-economic status (SES) than the average SES in our sample,” Cardan noted. “But they both showed this delayed-like pattern in neurocognitive development compared to their respective low-pollution peers.”
After observing the adolescents over a two-year period, the researchers noticed clear differences in development between the exposed groups. Young people living in low-pollution environments showed all the expected signs of biologically and psychologically healthy maturation. Over a two-year period, these control groups experienced normal thinning of the gray matter in their brain cortex.
Young people with low pollution also showed increased connectivity in adult-like brain networks, moving away from childhood brain patterns. At the same time, mean scores on cognitive memory and attention tasks increased steadily. These results confirmed that the researchers’ measurements accurately captured the normal transition to adolescence.
In contrast, teens living in areas with high levels of particulate matter and surface ozone did not show these typical developmental milestones. Their brains had less structural thinning and less mature networks than the brains of their unexposed peers. The brain networks of young people in the high-contamination group remained close to childhood patterns and showed less improvement in cognitive performance tasks.
“From a statistical perspective, the magnitude of isolated associations is small,” Cardan said. “However, given the importance of healthy cognitive development and its downstream effects on multiple domains such as young people’s mental health, resilience, and academic success, this result has practical significance that may exceed the statistical effect size.”
Although these findings are very informative, this study includes several potential limitations. Cardan emphasized that readers should not confuse slower developmental rates with lower overall intelligence. “Lower-than-expected growth in neurocognitive indicators is different from general cognitive decline (the former is about trajectory, the latter about overall averages),” Cardan said. “Our findings in this study are primarily about differences in trajectories in cognition, rather than overall averages of cognitive ability.”
Another important consideration involves the timing of air quality measurements. “Our method gives us some confidence in the specificity of the association,” Cardan said. “However, only the brain and cognition measures were longitudinal in this study, and the air pollution measurements were not longitudinal, so we cannot infer a causal relationship here.”
Air pollution data were based entirely on outdoor air quality in the participants’ area of residence at the start of the study. This means measurements may not capture the exact amount of pollutants each child actually inhaled while attending school or spending time indoors. This data also does not take into account families who moved to another region or city during the two-year study period.
Future studies could investigate the specific chemical components that make up particulate matter in different geographic regions. By examining specific chemicals, scientists can gain a detailed understanding of which elements pose the highest risk to the developing nervous system. “We plan to expand our analysis to more stages of the ABCD study, including ages 13 and beyond,” Cardan said.
The study, “Neighborhood Air Pollution Is Associated with Slower Neurocognitive Maturation in Early Adolescence,” was authored by Omid Kardan, Chakriya Sereyotin, Kathryn E. Schertz, Mike Angstadt, Alexander S. Weigard, Mark G. Berman, Mary M. Heitzeg, and Monica D. Rosenberg.
