LAUSR

Air pollutants pose risks to human health, especially in densely populated cities. We compared the interception of suspended particles and metal elements by four sidewalk tree species with different leaf surface wettability (based on contact angle), leaf area and phenology, in Taipei, Taiwan. Suspended particles were enriched 2.0-2.5 times in throughfall relative to rainfall, due to wash-off of suspended particles deposited on leaf surfaces during rainless periods. The enrichment in throughfall was greater in tree species with larger leaf areas. Despite greater concentrations of suspended particles in rainfall during the low leaf area period, the enrichment was greater in the high leaf area period, indicating that leaf area was a key factor affecting canopy interception of pollutants. Throughfall enrichment of suspended particles positively correlated with water quantity, indicating that air pollutants intercepted by tree canopies were not fully washed off by rainfall. Annually, approximately 830 g of suspended particles were intercepted and washed off from one tree canopy, with a crown area of 42 m2 . Scaling up, as a rough estimate 72.7 tons of suspended particles were intercepted annually by the 90,000 sidewalk trees in Taipei city. The metal elements copper (Cu), Chromium (Cr) and aluminum (Al) were enriched in throughfall compared to rainfall. However, lead (Pb) was depleted in throughfall indicating greater interception than wash-off. Based on our results, leaf area and length of foliated period are key characteristics affecting canopy interception of particulate matter and associated metal elements, while leaf surface wettability is of secondary importance. This article is protected by copyright. All rights reserved.