Study On Particulate Matter And Its Size Fractions Deposited On Common Greening Species In Nanjing

Atmospheric particulate matters have been the primary air pollutants in the world's major cities and are harmful to human health.Greening species always play an important role in reducing air pollution of particulate matters and improving air quality by acting as biological filters to capture atmospheric particulate matters.The spatial and temporal distribution characteristics of particulate matters were studied in six different function zones in Nanjing.On the purpose of studying the retention capacity of particulate matters,8 species of representative plants in Nanjing were chosen to systematically analyze the deposition of particulate matters with different sizes on them by using direct sampling and electron microscope analysis methods.The mechanism that micro structure of leaf surface how to affect the capability of PM_2.5 was also discussed in this paper.The main conclusions can be drawn as follows:?1?The contents of PM,PM10 and PM_2.5 in foliar dust varied greatly with different seasons and the highest value of which occurred in winter.PM_2.5retention capacity per unit leaf area at all seasons was 6.22?g/cm2?spring?,3.58?g/cm2?summer?,7.32?g/cm2?autumn?and 11.23?g/cm2?winter?.The contents of particulate matters showed significant difference among different function zones.The sequence was industrial area,commercial area,transport area,residential area,teaching area,tourist area and control area.?2?Over 94% of PM deposition on plants' leaf surface were PM10,PM_2.5 accounted for over73%,whereas,course particles accounted for less than 6%.The mass fraction of PM10 was over than 66.9%,that of PM_2.5 was 18.3%,and the mass fraction of course particles was 33%.The ability of the upper surface of the plant leaves to retain atmospheric particles was significantly stronger than that of the lower surface.The content of PM,PM10 and PM_2.5 per unit leaf area showed significant difference among the plant species,with the variation ranges of 32.35 83.92?g/cm2?PM?,20.99⁵7.51?g/cm2?PM10?and 6.27³2.77?g/cm2(PM_2.5),respectively.Cerberus deodara,Pinus tabuliformis and Sabina chinensis were efficient species in capturing PM_2.5.Platanus acerifolia,Photinia×fraseri and Osmanthus fragrans had a medium ability to accumulate PM_2.5.Less efficient species were Pittosporum tobira and Cinnamomum camphora.On the whole,the adsorption of coniferous species was high than that of broad-leaf species.The arbor species had strong ability to strand the total PM,but the difference of PM10 and PM_2.5 between arbor species and shrub species was not significant among the broad-leaf species.In the future construction of greening in Nanjing,we can select coniferous and arbor species such as Cerberus deodara,Pinus tabuliformis,Sabina chinensis and Platanus acerifolia in order to bring better ecological benefits to Nanjing.?3?The captured amount of PM_2.5 per unit leaf area among the plant species had positive correlation with stomatal density,stomatal size and villus density.Fluted or grooved leaves can also strand more PM_2.5 and the grooves too broad or too narrow were not beneficial to trap PM_2.5.The capture amount of PM_2.5 on leaf surface increased with increasing groove depth.