Find in Library

PM_2.5 concentrations in urban areas are highly variable, both spatially and seasonally. To assess these patterns and the underlying sources, we conducted PM_2.5 exposure measurements at the adult breath level (1.6 m) along three ~5 km routes in urban districts of Mainz (Germany) using portable low-cost Alphasense OPC-N3 sensors. The survey took place on five consecutive days including four runs each day (38 in total) in September 2020 and March 2021. While the between-sensor accuracy was tested to be good (R² = 0.98), the recorded PM_2.5 values underestimated the official measurement station data by up to 25 µg/m³. The collected data showed no consistent PM_2.5 hotspots between September and March. Whereas during the fall, the pedestrian and park areas appeared as hotspots in >60% of the runs, construction sites and a bridge with high traffic intensity stuck out in spring. We considered PM_2.5/PM₁₀ ratios to assign anthropogenic emission sources with high apportionment of PM_2.5 in PM₁₀ (>0.6), except for the parks (0.24) where fine particles likely originated from unpaved surfaces. The spatial PM_2.5 apportionment in PM₁₀ increased from September (0.56) to March (0.76) because of a pronounced cooler thermal inversion accumulating fine particles near ground. Our results showed that highly resolved low-cost measurements can help to identify PM_2.5 hotspots and be used to differentiate types of particle sources via PM_2.5/PM₁₀ ratios.