A paper published in Environment International with data from 37,000 children from Vancouver found that Children living in areas with higher air pollution due to PM2.5 particles and very low levels of green space might have up to 62% increased risk of developing ADHD. On the contrary, children living in greener and less polluted areas have a 50% lower risk of developing ADHD.
The green space analysis revealed that participants living in areas with a greater percentage of vegetation had a lower risk of ADHD. More specifically, the results show that a 12% increase in vegetation percentage was associated with a 10% reduction in the risk of ADHD.
The opposite association was observed with PM2.5: participants with a higher exposure to fine particles had higher risk of ADHD (every 2.1 µg/m³ increase of PM2.5 translated into an 11% increase in the risk of ADHD).
The researchers also looked at the effect of NO2 and noise on the prevalence of childhood ADHD, but no associations were found there.
Additionally, the beneficial effects of greenness and harmful effects of PM2,5 exposure mitigate each other. It is not clear whether this is because greenness lessens the exposure to PM2,5 (for example, by taking taking it up from the air).