Study On The Differences In The Retention Of Particulate Matter On The Leaf Surfaces Of Eight Common Garden Plants In Hangzhou

As the pollution of particulate matter（PM）in the atmosphere is becoming increasingly severe,the plants can effectively reduce the concentration of PM by retaining it on their leaves.In this paper,eight common garden plants in Hangzhou were selected as the objects of study to quantitatively analyze the difference of residues different particle sizes in leaf surface and wax layer by the method of rinsing and weighing.Scanning electron microscopy（SEM）and software were used to observe the micro morphology features of the leaf surfaces and the retained particles and to measure the amount of residual particles per unit leaf area.During the process,Confocal Laser Scanning Microscope（CLSM）was applied to detect the morphology features of the leaf surfaces and the relationship between the roughness of the leaf surfaces and the number of the retained particulates were analyzed quantitatively.In addition,X-ray energy spectrometer（EDS）point analysis of particulate matter elements on blades to analyze the elemental composition of the particles,the elements in the soil were measured by ICP-OES to locate the possible sources of the particulates.The main results are as follows:There were significant differences in leaf surface and wax layer per unit leaf area retention of PM_2.5,PM₁₀ and TSP.In spring and autumn,the same plant had different retention amounts of different particle sizes and the same particle sizes,the difference can be tens of times.In spring the quantity of the retained particles per unit leaf area followed the order:F.japonica>I.latifolia>E.japonica>M.grandiflora>R.pulchrum>C.camphora>T.repens>A.julibrissin;in autumn the order is:I.latifolia>F.japonica>A.julibrissin>T.repens>M.grandiflora>R.pulchrum>E.japonica>C.camphora.TSP retention in autumn was generally greater than that in spring.In the two seasons of spring and autumn,in different PM on the surfaces of blades,the proportion of particles larger than 10μm is the largest.The retention of PM_2.5,PM₁₀ and TSP was significantly different for leaf surface and wax layer of different vegetation types,and there were differences between different seasons of the same vegetation type.The TSP retention ability of shrubs on leaf surface was significantly higher than that of trees and herbs,while that of waxy layer trees was higher than shrubs and herbs.Plant height and leaf characteristics have a great influence on the retention of atmospheric particulate matter.The results revealed that the ability of the leaves to retain particulates is attributed to the synergy of multiple micro structures on the leaf surfaces,such as grooves,folds,small chambers,flocculus projections,long villi,pubescent hairs,and waxes.Among the different particle sizes,the number of PM_2.5 retained on the surfaces of the different plant leaves was the most,while a much smaller number of particles with sizes larger than 10μm was retained.And the roughness of the leaf adaxial surfaces in spring are closely related to the number of the retained particulates.The rougher the surfaces and the more rugged the folds and the grooves are,the stronger the retention ability is.In spring the elements of the retained particulates are mainly 11 kinds,which was proved to come from the soil dust after being compared with the elements in the soil samples.In autumn,there were 32 kinds of main elements in particulates,some of which come from the natural world and some from non-natural such as construction cement dust,coal dust and metallurgical dust.These research results provided an important theoretical scientific basis for the mechanism of PM adsorption by plants and a strategy for the reasonable selection of garden dust-retaining tree species.