A Spanish study investigating the effects of traffic-related air pollution on children walking to school has found higher levels of particulate matter and black carbon were associated with decreased growth in working memory capacity. Working memory capacity grows during childhood (and tends to fall in old age).
The study involved 1,234 children aged 7-10, from 39 schools across the city of Barcelona. The children were tested four times over a year to establish their developmental trajectories in working memory and inattentiveness. Average particulate matter, black carbon, and nitrogen dioxide, were estimated for the children’s walking routes using standard measures.
None of the pollutants were associated with inattentiveness. The effect of NO2 on working memory was inconclusive. However, increased concentrations of particulate matter and black carbon were associated with a reduction in the annual growth of working memory of 4.6% and 3.9%, respectively. Boys were more affected than girls.
The study followed an earlier study showing that exposure to traffic-related pollutants in schools was associated with slower cognitive development. Research has previously shown that 20% of a child's daily dose of black carbon (which is directly related to traffic) is inhaled during urban commutes.
The finding emphasizes that even “short exposures to very high concentrations of pollutants can have a disproportionately high impact on health”, and this may be especially true for children, with their smaller lung capacity and higher breathing rate.
The researchers emphasize that the solution for parents is not to stop children walking to school, since those who commute by car or public transport are also exposed to the pollution. Rather, the aim should be to try and find (or make) less polluted, low-traffic paths to school.
 Impact of commuting exposure to traffic-related air pollution on cognitive development in children walking to school. Environmental Pollution [Internet]. 2017 ;231:837 - 844. Available from: http://www.sciencedirect.com/science/article/pii/S0269749117318997