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.

Key message: Whereas cold temperatures and artificial smoke pollution (during World War II) cause negative pointer years in northern Fennoscandian downy birches, mass outbreaks of Epirrita autumnata L. and Operophtera brumata Bkh. are the strongest growth-influencing and -synchronizing factor. Variations in radial tree growth of downy birch can be affected by short-term environmental changes. Here we examine the tree-ring width of downy birch trees for signals caused by three different disturbance factors: climatic extremes, insect outbreaks, and artificial smoke employed to hide the German battleship Tirpitz during World War II at the Kåfjord in northern Norway. Besides growth/climate response analysis using gridded climate data and a tree ring width-chronology of the studied birch trees, we analyze missing rings, pointer years, and the ability of recovery after severe disturbances on an individual tree basis using the percent change of the trees’ basal area increment with respect to a reference period. The downy birches reveal (1) a significant positive correlation with May and June temperatures, (2) a high growth sensitivity to moth epidemics (Epirrita autumnata L. and Operophtera brumata Bkh.), and (3) a distinct growth deviation in the year of intense but short-term artificial smoke pollution. We conclude that downy birches are not exclusively sensitive to unusual cold temperatures, but short-term artificial pollution and insect outbreaks cause similar growth declines in the year of occurrence. Whereas for temperature and pollution, the growth response is less coherent among trees, and fades within 2 years, the insect outbreaks synchronize growth among all downy birches. Growth declines during years of mass insect outbreaks can further be amplified by cold May and June temperatures. Our findings thereby improve the understanding of competing disturbance factors on single birch trees but also on the growth of a whole site in Fennoscandia and facilitates the detection of disturbances in birch chronologies.

Die Körpergrößen von Kindern und Erwachsenen sind sehr verschieden und können zu einer unterschiedlichen Belastung durch PM2.5-Partikel führen. Wir haben die PM2.5-Belastungen von Fußgängern auf einer 5.5 km langen, zirkulären Strecke entlang von Kindergärten und Schulen in Mainz (Deutschland) gemessen. Die Messungen wurden im November 2019 an acht aufeinanderfolgenden Tagen in zwei Höhen, der Atemhöhe von Erwachsenen in 1.6 m und Kindern in 1.0 m, mit Alphasense OPC-N3 Low-Cost-Sensoren durchgeführt. Wir fanden heraus, dass, unabhängig von der Messhöhe, anhaltend ruhige Wetterbedingungen mit geringen Windgeschwindigkeiten < 1,0 m/s und fehlendem Niederschlag zu erhöhten PM2.5-Belastung von über 60 µg/m³ führten. Der Vergleich der beiden Messhöhen ergab, dass Kinder an sechs Tagen mehr als 20 % höheren Konzentrationen ausgesetzt waren (p < 0.01), an einem Tag betrug dieser Unterschied sogar über 80 %. Die Unterschiede nahmen im Allgemeinen mit zunehmender PM2.5-Konzentration zu, weitgehend unabhängig von der Position entlang der Strecke, aber von Tag zu Tag stark variierend. Diese Ergebnisse werden durch eine Mikroklimasimulation von Verkehrsabgasen mit ENVImet gestützt. Die stärksten Höhenunterschiede treten hier in der Nähe von Straßen mit hoher Verkehrsintensität auf. Unsere Ergebnisse zeigen, dass Kinder erheblich höheren PM2.5-Konzentrationen ausgesetzt sind als Erwachsene, ein Phänomen, das in den offiziellen, immobilen Messstationen, normalerweise nicht beobachtet werden kann, da diese die Feinstaubpartikel nur auf einer Messhöhe erfassen.