PM2.5 exposure differences between children and adults

Heights of children and adults vary substantially and may cause different exposure to PM2.5 particles. We measured pedestrian PM2.5 exposure by foot following a 5.5 km route along kindergartens and schools in Mainz (Germany). Measurements were conducted in November 2019 on eight consecutive days at two heights, the potential breathing heights of adults in 1.6 and children in 1.0 m using Alphasense OPC-N3 low-cost sensors. We found that regardless of height level, persisting calm weather conditions including low wind speeds <1.0 m/s and lack of precipitation lead to increased PM2.5 exposure exceeding 67.8 μg/m3. Comparing the height levels revealed that the children were exposed to >20% higher concentrations on six days (p < 0.01), on a single day this difference exceeded 80% (24.7 μg/m3). Differences generally increased with increasing PM2.5 concentrations, though the latter are largely independent of the position along the route but varied strongly among days. These findings are supported by a microclimate simulation including traffic exhaust emissions revealing strongest height differences nearby streets with high traffic intensities. Our results demonstrate that children are exposed to considerably higher levels of PM2.5 that are typically not observed in the stationary networks recording aerosols on only one level.