Airborne particulate matter (PM) has become a serious environmental problem and harms human health worldwide. Trees can effectively remove particles from the atmosphere and improve the air quality. In this study, a washing and weighing method was used to quantify accumulation of water-soluble ions and insoluble PM on the leaf surfaces and within the wax of the leaves for 17 urban plant species (including 4 shrubs and 13 trees). The deposited PM was determined in three size fractions: fine (0.2–2.5 μm), coarse (2.5–10 μm), and large (> 10 μm). Significant differences in the accumulation of PM were detected among various species. The leaves of Platycladus orientalis and Pinus armandi were the most effective in capturing PM. Across the species, 65 and 35% of PM, on average, deposited on the leaf surface and in the wax, respectively. The greatest PM accumulation by mass on leaves was in the largest PM size fraction, while the accumulation of coarse and fine particle size fractions was smaller. Water-soluble ions accumulated on the leaf surfaces contributed 28% to the total PM mass, on average. This study demonstrated that leaves of woody plants accumulate PM differently, and the most effective plant species should be selected in urban areas for attenuating ambient PM.

Tree-level intrinsic water-use efficiency (iWUE) is derived from the tree-ring ¹³C isotope composition (δ¹³C) and is an important indicator of the adaptability for trees to climate change. However, there is still uncertainty regarding the relationship between long-term forest ecosystem carbon sequestration capacity and iWUE. To determine whether elevated atmospheric CO₂ concentration (Ca) increase iWUE and tree growth (basal area increment, BAI), dendrochronological methods and stable isotope analyses were used to examine annual changes in the tree-ring width and carbon isotope composition (δ¹³C) of Platycladus orientalis in northern China. The iWUE derived from δ¹³C has increased significantly (p < 0.01). Long-term iWUE trend was largely and positively driven by the elevated atmospheric CO₂ concentration and temperature. We observed a general increase in averaged BAI, which had significant positive correlation with iWUE (R² = 0.3186, p < 0.01). Increases in iWUE indeed translated into enhanced P. orientalis growth in semi-arid areas of northern China. Elevated atmospheric CO₂ concentration significantly (p < 0.01) stimulated P. orientalis biomass accumulation when Ca was less than approximately 320 ppm in the early phase; however, this effect was not pronounced when Ca exceeded 320 ppm.