| In recent years, air pollution become more and more serious with the development of economy and increase of energy consumption, especially the pollution caused by atmospheric particulate matters. Plant has the ability to purify the particulate pollution as it was the main part of city greening. A new method for quantifying fine particulate matter (PM2.5, d≤2.5 μm) and other atmospheric particulates retained by tree leaves was established in this research. Quantitative characteristics of dust retention by foliage and the effect of environment, season, precipitation had been analyzed at two study sites including Beijing (primary) and Chongqing (vice). The distribution characters of foliar dust are mainly studied by Mastersizer 2000 laser particle size analyzer. The relations between the dust retention ability and microconfigurations of leaf epidermis were observed through S3400-N scanning electron microscope (SEM). All research in order to provide scientific basis for selection of efficient dust retention afforestation tree species. The main conclusions of this study can be summed up as follows:(1) PM2.5 retention capability of Beijing species leaves is as follow:Pinus tabuliformis> Amur honeysuckle> Syringa reticulate> Euonymus japonicus> Acer truncation> Fraxinus pennsylvanica, and that of Chongqing species is Ficus microcarpa> Osmanthus fragrans> Magnolia gradiflora> Pittosporum tobira> Ficus virens> Pittosporum tobira> Bischofia polycarpa.The order of PM10 retention ability of Beijing species PM10 decreased in the order of:Pinus tabuliformis> Amur honeysuckle> Euonymus japonicus> Syringa reticulate> Fraxinus pennsylvanica> Acer truncatum. The retention ability of Chongqing species is the same of PM2.5 retention ability.Total particulate retention capability of Beijing species leaves is the same as total particulate’s. Ficus microcarpa, Osmanthus fragrans, Magnolia gradiflora have the best retention capability in Chongqing species,243.8117 μg/cm2,169.4157 μg/cm2,141.1328 μg/cm2 respectively, while Bischofia polycarpa and Bambusa multiplex have the poor capability, only 63.1896 μg/cm2 and 65.7453 μg/cm2. Pittosporum tobira and Ficus virens are between them.(2) Plant leaves retention capability is higher in pollution area than in clean area, whatever to total particulate, or to PM10 and PM2.5.(3) Particle-retention characteristics of plant leaves change by the season, local seasonal pollution characteristics should be considered in selection of efficient dust-retention plants when take the trees advantage in different seasons into account.(4) Particle-retention of Syringa reticulata, Fraxinus pennsylvanica, Acer truncatum has a very strong capacity of "plasticity". Although the unit leaf area retention quantity is small, compared to shrub Amur honeysuckle and Euonymus japonicus, the plant green quantity to be much larger, so they are also plants with high efficiency of dust-retention and good landscape effect.(5) The grain size distribution of the foliar dust obeys the normal distribution with single-apices and multimodal-apices. The size of foliar dust mainly concentrates in 10-50 μm. Judging from the average particle size (Dav):Acer truncatum< Syringa reticulate< Euonymus japonicus< Bambusa multiplex< Fraxinus pennsylvanica< Magnolia gradiflora< Ficus microcarpa< Osmanthus fragrans<Amur honeysuckle< Pittosporum tobira< Pinus tabuliformis. Judging from the slm:Acer truncatum> Syringa reticulate> Euonymus japonicus> Bambusa multiplex> Osmanthus fragrans> Ficus microcarpa> Fraxinus pennsylvanica> Magnolia gradiflora> Pinus tabuliformis> Amur honeysuckle> Pittosporum tobira.(6) The micro-configurations of leaf epidermis are observed through scanning electron microscope (SEM), the results show that the particle-retaining capacity increase with the enlargement of stomata size, but has nothing to do with the amount of stomata. The particle-retaining capacities of the micro-configurations of leaf epidermis were decreased in the order of secretions> trench> groove> wrinkle> strip raise (Beijing species); Deep groove> cilium> shallow groove> cell> smooth leaf epidermis (Chongqing species). |
