The Influence Of Farming Ploughing On PM₁₀ And PM_2.5 In The Suburbs

The inhalable particles(P_M10) and fine particulate matter(PM_2.5) in the atmosphere bring a great threat to the environment and human health, it becomes a heavy problem of atmospheric pollution. For now, the major sources of P_M10 and PM_2.5 in China are coal combusition, automobile exhaust emissions, soil dust and so on. Privious studies mainly focused on the compositions of P_M10 and PM_2.5 which come from coal and automobile exhaust source, the studies about PM come from soil source were ignored. Farming activities is a important source of soil dust in P_M10 and PM_2.5, especially when highly intensity agriculture activities such as land using, farming and fertilizers utilization were carrying out in suburb, the soil structure was destroied and resulted fine soil particles diffusing with heavy metal and other residues escape to the atmosphere, which is hazard to the atmospheric environment.The P_M10 and PM_2.5 samples were collected at the Jiangxia field of Wuhan Botanical Garden of the Chinese Academy of Sciences and in four different seasons during July 2013 to June 2014. We discussed the temporal and spatial changes of the mass concentration of P_M10 and PM_2.5 basing on the meteorological factors（including temperature, wether and etc）. The element, the component and mineral characteristics were analysed, and using Enrichment factor method and Chemical mass closure analyse the composition of the samples. By combining the mineral components and the particle size distribution in P_M10 and PM_2.5 in ploughing time and non-ploughing time, farming activities influence P_M10 and PM_2.5were discussed. The main conclusions are as follows:（1） The daily average concentration of P_M10 and PM_2.5 in winter is highest at the sampling site, moderate in spring and autumn and lowest in summer. There are exceeding pollution during the three seasons except in summer. The daily mean concentration of P_M10 in summer, autumn, winter and spring respectively are 66.23μg/m3, 151.36μg/m3, 206.23μg/m3 and 159.01μg/m3, and the daily mean concentration of PM_2.5 respectively are 47.54μg/m3, 110.91μg/m3, 133.49μg/m3 and 110.83μg/m3. The exceeding rate of PM_2.5 is 100%. The correlation of P_M10 and PM_2.5 presents good, the average ratio of PM_2.5 and P_M10 is about 0.72, but the ratio of PM_2.5 and P_M10 in winter is 0.66.（2） The analyse of EF（enrichment factor） shows that Si and Ti in P_M10 and PM_2.5 are derived from soil or dust by the weathering of rock. Al, Cr, Mg, Mn are mainly from soil. The main source of Ca and Cu are anthropogenic pollution. The EF ofCd and Pb is higher than 100, the main source of Cd and Pb are automobile exhaust emissions, coal combusition and chemical metallurgical. The EF of Cd, Pb and Cu in PM_2.5 is higher than which in P_M10.（3） The eight water soluble ions, organic carbon（OC） and elemental carbon（EC） of P_M10 and PM_2.5 shows obvious seasonal variation, the concentration of P_M10 and PM_2.5 in winter is highest, moderate in spring and autumn and lowest in summer.The sample P_M10 and PM_2.5 is acidic, the proportion of total water soluble ions of P_M10 in summer, autumn, winter and spring respectively are 48.31%、43.97%、50.55% and 38.24%, the proportion of secondary ions（SO42-、NO3- and NH4+） of P_M10 respectively are 37.96%、39.17%、42.53% and 41.22%. The proportion of total water soluble ions of PM_2.5 in summer, autumn, winter and spring respectively are 25.86%、44.70%、47.17% and 40.63%, the proportion of secondary ions（SO42-、NO3- and NH4+） of PM_2.5 respectively are 21.83%、40.82%、41.60% and 37.73%. The concentration of OC in P_M10 ranges from 10.73 to 20.60 μg/m3, the concentration of EC ranges from 1.95 to 3.06 μg/m3, the ratio of OC and EC ranges from 5.50 to 6.73. The concentration of OC in PM_2.5 ranges from 8.42 to 15.36 μg/m3, the concentration of EC ranges from 1.43 to 2.59 μg/m3, the ratio of OC and EC ranges from 3.93 to 6.96.（4） The kaonilite, feldspar, hematite and magnetite in P_M10 and PM_2.5 were caused by disturbing soil, and the mica enriched at the particle which the size range from 2.5 to 10 μm. The disturbance of the soil has a greater influence on P_M10 than that on PM_2.5.（5） The peak of size distribution of mineral in P_M10 and PM_2.5 shifts to larger size, it resulted the proportion of the larger particle in P_M10（2.5-10 μm） and PM_2.5（1.0-2.5 μm） increasing at ploughing time in autumn. It showed that the disturbance of the soil contrubuted larger particle to P_M10 and PM_2.5.（6） According to the Chemical mass closure analyse, the organic matter（OM）, soil, SO42-, NO3-, NH4+, EC and others in P_M10 respectivelyare 23.99%, 18.18%, 14.89%, 14.16%, 6.31%, 2.49%, 19.98%. The OM, soil, SO42-, NO3-, NH4+, EC and others in PM_2.5 respectivelyare 26.62%, 13.44%, 16.28%, 11.39%, 7.05%, 2.97%, 22.25%.