Study On The Dust-retention Effect Of The 18 Kind Common Urban Greening Trees In Dalian

Air pollution is an inescapable product of the process of urbanization process. The composition of the air pollutants is complex, which the particulate matter is the major component. The urban tree species can purify the air by various ways, one of that is the detaining dust depending their leaves. Dalian is the first batch of Chinese Ecological Tourism City, but in recent years, it often suffers from the air pollution. This study collects 129 samples of 18 common trees in the city to measure the dust detained on the leaves, analyse the characteristics of size distributions of foliar dust, and observe the micro-structures of leaf, in order to investigate the dust-retention ability of these trees. After analysis, the results are as follows:(1)The results of dust retention show that conifer can detain more particulate matter than hardwood, and the shrub do the least. Among conifer, Cedrus deodara(Roxb.) G. Don is optimal, Platanus acerifolia(Aiton) WilldandPopulus ×canadensis Moench are prominent within hardwood.However, Sophora japonica L.f. pendula(Spach) Hort. ex Loudon, Sophora japonica LinnandSalix babylonica Lcatch the particulate matter is very few, Berberis thunbergii var. atropurpurea Chenault is the best shrub to detain particulate, and Buxus rugulosa Hatussecondly.(2)The leaves live on the different heights of the plant have different dust detaining ability. There is a significant negative correlation between dust detained and height, especially the large trees,the small ones are on the contrary. Conifer is more obvious than broadleaf trees, and the magnitude of the decline is larger than the latter. The leaves angle also has certain influence on the dust retention ability. Generally, a few of dust was caught between 0°-60°, but most within 60°-120°.(3)The particle size analysis shows that the characteristics size of foliar dust are different on various plants. The most distribution is approximate normal distribution, and has two peaks, including bi-peak and single-peak. According to the particle accumulation distribution table, we can determine the plants have adsorption capacity in view of each size particle; the average diameter tells us shrub is partial to the adsorption of large particles, broadleaftrees for fine particulates.(4)Trough the relationship between leaf structure and the dust retention ability, we know the structure of leaves of Platanus acerifolia(Aiton) Willd, Ehrhar f.atropurpurea(Jacq.) Rehd, and Berberis thunbergii var. atropurpurea Chenaultare the most conducive to catch the leaf surface dust;Sophora japonica Linn,Sophora japonica L.f. pendula(Spach) Hort. ex Loudonand Ligustrum lucidum W. T. Aitonhave too smooth surface to catch less dust. Furthermore, the leaf epidermis coated with wax layer of Buxus microphylla can absorborganic gases.Altogether, through the several researches, the combination of conifer+ hardwood+ shrubs is the best for dust retention, hardwood+ shrubs are second. However, the single tree species configuration will cause the dust retention ability is too simple, and go against to the adsorption of particles. Therefore, Cedrus deodara(Roxb.) G. Don can be planted as first choice in the urban greening, particularly in heavy pollution area, Platanus acerifolia(Aiton) WilldorPopulus ×canadensis Moench is the subsidiary role. If necessary, Berberis thunbergii var. atropurpurea Chenaultis also chosen, there will be an obvious effect in dust retention.