Abstract
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 (0.2-2.5μm), coarse (2.5-10μm), and large (> 10μm). 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.
Highlights
Airborne particulate matter (PM), consisting of particles with aerodynamic diameters in the range of 0.001-100 μm, is a major atmospheric pollutant (Pope III and Dockery 2006; WHO 2006)
The lowest and highest surface PM deposition were found in P. tomentosa 217 (12.5 μg cm-2) and P. armandi (56.9 μg cm-2)
Fraction surface accumulation was 3.5 μg cm-2, or 10% of the total insoluble PM deposition. These present results showed that shrubs accumulated more mass of large size fraction PM on leaf surface than most of the trees, except that P. orientalis and P. amandi which showed slightly higher accumulation than that of shrubs
Summary
Airborne particulate matter (PM), consisting of particles with aerodynamic diameters in the range of 0.001-100 μm, is a major atmospheric pollutant (Pope III and Dockery 2006; WHO 2006). Enhanced the deposition flux to the surface is the benefit for reducing pollutant concentrations near the ground and exposure of people in urban areas. Compared with other urban surfaces, vegetation enhances deposition of particles because of the finely divided structure of many leaves, especially conifers. They have a larger collecting surface per unit ground area, and reduce the laminar boundary layer that limits the particles uptake. Two key features of this study were investigation of: 1) particles deposited onto the leaf surface and into the wax as a function of three particles size fractions; and (2) the accumulation of water-soluble ions by the leaf surface
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