Forest structural traits influence concentrations of snow deposited particulate matter and metal elements in urban forests in NE China: Implications for winter air pollution control in high-latitude regions of the Northern Hemisphere

Abstract

High-latitude Northern Hemisphere cities face serious wintertime particulate matter (PM) pollution, but the amounts and compositions of tree-species-specific PM and metal deposition remain poorly defined. This study analyzed snow samples (snow depth, snow water equivalents (SWE), PM content (W10μm–2mm, W2μm–10μm, W0.45μm–2μm), metal concentrations (Ca, K, Mg, Fe, Zn, Cu, Mn, Ni, Cr, Pb, Cd) and tree characteristics (tree height, diameter at breast height, biomass, etc.) from seven urban plantations and one open site in the city of Harbin, Northeast China in the winter heating season with PM pollution. Our results revealed that tree size and broadleaf-conifer leaf traits are good indicators of PM deposition by the snow. The snow depth and SWE value were found to be significantly higher in broadleaf plantations than those in coniferous plantations. But concentrations of Ca, K, Cu, Mn, Pb and larger PM (W10μm–2mm) in snow meltwater from coniferous plantations were 2-5-fold and 2-3-fold higher than those from broadleaf plantations. Remarkably, the Picea koraiensis plantation (Pm) had relatively high W10μm–2mm and metal concentrations in snow samples, while the open site had the lowest W10μm–2mm and metal concentrations. Those could be attributed to the combined effect of tree sizes, species and aboveground biomass. Nearly 95% of the uncertainty tests showed the inter-species differences were independent of sampling locations, indicating the high reliability of the findings. Our findings indicated that coniferous trees with greater aboveground biomass could favor snow deposition of PM and specific metals, which supports forests-based urban PM control in winter via snow interception.