| With the rapid increase of urbanization process,city vehicles increase rapidly,air pollution has become a serious environment problem for majority countries and regions,and particle matter(PM)pollution was known as an important limiting factor to improve city air quality,especially the street environment particle pollution.Road greenbelt could improve the air quality by retarding and adsorbing particles,and current researches mainly focus at the particle attenuation of roadside greenbelt,however,several researches focuses on the particle attenuation of greenbelts between motor way and bicycle lane which could protect the pedestrian.In order to attenuate the particle concentration and improve the street air quality,it is very urgency to constructing efficient roadside greenbelt which aims to purifying the particle concentration.Based on this,this research explored the accumulation amount of different sizes particles of plant leaves in different sample sites,and then combined the PM accumulation ability and leaf morphological and physiological characteristics to select the efficient plants;analyzed the characteristics of particle sizes distribution upon leaf surfaces of different plant species;the PM characteristics of plant leaves of different crown altitude and direction in road environment;in addition,this research explored the PM attenuation efficiency of different roadside greenbelts,analyzed the correlation between PM attenuation efficiency and greenbelt structure parameters and meteorological factors,and then explored to construct the efficient model and optimizing strategy of roadside greenbelt to attenuate PM.The main research results as follows:(1)24 plant species were selected both in polluted area and control area,and the amount of different sizes particles upon leaf surfaces were measured through gravimetric method.The results indicated that the particle accumulation amount of different sites and different plant species were significant different,the level of pollution and plant species has obvious influence on the particle amount upon leaf surfaces.Dust fall were occupied majority part of the particles upon leaf surfaces which occupied more than 80% and PM0.2-2.5 just occupied around 2% whether it is in polluted area or in clean area.In addition,The SLA value of leaf in polluted sites was significant increased than clean sites through measured the value of leaf morphological and physiological index,pigment content,pH and RWC value was significant decreased.These results indicated that plants in polluted sites were influenced in some extent,and these parameters could be used to select tolerant plants.Therefore,this research divided 24 plant species into 4 degrees(better,good,general and worse)through combine subordination function method and clustering method based on the PMs accumulation ability and leaf morphological and physiological index.Results shown that Eriobotrya japonica,Rhododendron simsii,Nerium indicum,Jasminum mesnyi,Osmanthus fragrans,Mahonia confuse and Photinia serrulata belong to the better degree;Platanus acerifolia,Koelreuteria ipinnata,Morus alba,Loropetalum chinense,Magnolia grandiflora,Trachycarpus fortune,Viburnum odoratissimum,Pyracantha fortuneana,Reineckia carnea and Ligustrum lucidum belong to the good level;Elaeocarpus sylvestris,Sophora japonica,Pittosporum tobira,Parthenocissus tricuspidata and Iris tectorum belong to the general level,however,Ginkgo biloba and Prunus cerasifera belong to the worse level.(2)Three type plant species in three sites with different pollution levels(i.e.serious polluted,moderate polluted and control area)were selected to analyze the distribution characteristics of particle upon plant leaves.The results indicated that the particle number of all kinds of plant in serious polluted area was the maximum and in control area was the least,the particle number of adaxial of upper surfaces was more obvious than abaxial of upper surfaces and lower surfaces,and the particle amount of 2yr needle leaf was significant greater than 1yr needle leaf.Fine particles were counted main part of leaf particles which almost occupied more than 95% of the leaf total particles.Based on the SEM observation of leaf microstructure and particle distribution,it can be found that particle matters mainly gathered at cell and vein of Cinnamomum camphora leaves,and the stoma of lower leaf surfaces also could adsorb particle when located at serious polluted area;particle matters mainly adhered at hairs and groove of upper and lower leaf surfaces of R.simsii;1yr needle leaf of Cedrus deodara adsorb particles mainly depend on the prismatic structure,and its ability of adsorb particles was relatively weak than other species because the leaf surfaces covered intensive wax crystal;2yr needle leaf of C.deodara has obvious stoma line,and it could adsorb particles through stoma and its surrounding structure.In addition,each kind of plants has their own adsorption characteristics by comparing the particle cover density of three type plants,the leaf with hairs has the biggest accumulation ability of particle matters at control plot;however,in moderate and serious polluted area,the accumulation number of particles mainly depended on the air particle concentrations.(3)This research explored the PM characteristics of different crown sites of plants within street environment.Results shown that the leaf PM amount of lower layer was higher than middle layer and high layer,and the difference of leaf PM amount of middle layer and high layer was not obvious.The leaf PM amount of road side leaf was significant higher than the opposite site,and the difference of herb was more obvious than trees.(4)This investigation measured the attenuation efficiency of different trends of roadside greenbelt to PMs.Results indicated that the attenuation efficiency difference among different trends of roadside greenbelt was significant,the attenuation efficiency of roadside greenbelts which perpendicular or have a certain angle to main wind direction was better than the roadside greenbelt which paralleled to main wind direction.In addition,the larger particle(TSP and PM10)attenuation efficiency of roadside greenbelts was higher than fine particle(PM2.5).This research proposed the theory of layer shelterbelt porosity to explore the influence of greenbelt structure to the PM attenuation efficiency.Results indicated that shelterbelt porosity has significant influence on the PM attenuation efficiency,especially the shelterbelt porosity of 0 ~ 2m.In addition,results indicated meteorological factors have significant effect on the PM attenuation efficiency,nevertheless the effect of meteorological factors to different size particles were different.The influence order of meteorological factors to TSP and PM2.5 attenuation efficiency was relative humidity > wind speed > temperature,and to PM10 attenuation efficiency was wind speed > temperature > relative humidity.(5)Based on the above theoretical research and some previous results,this paper explored to construct the plant selection and vegetation configuration theory of roadside greenbelt which aimed to attenuate PM concentration of bicycle lane,and then proposed some suggestions of plant selection,vegetation configuration and final management strategy for roadside greenbelt design and optimization in Wuhan. |
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