| With the development of China accelerating in recent years, the PM2.5 pollution is becoming more and more serious, which causes problems such as frequent haze, visibility reduction and human health, affecting the normal life of us, which has received extensive attention from all sectors of the community. In the meantime, for PM2.5 source from different regions or the same region in different periods are not the same, the environment and health problems are also different. Therefore, it is important to explore the pollution characteristics and sources of PM2.5 in different regions in different periods to establish the relevant policies for the prevention and treatment of PM2.5.First, we collected PM2.5 daily monitoring data of Lanzhou by China air quality real time publishing platform of environmental monitoring station from 2013.1.26 to 2016.1.30, and some PM2.5 samples in different periods（heating period, dust and non-heating non-dust periods）. Then we measured water-soluble ions and inorganic elements of PM2.5 by ion chromatography and inductively coupled plasma mass spectrometry to evaluate the temporal and spatial distribution and chemical composition of pollution characteristics of PM2.5 in Lanzhou. At last, we analyzed the source of PM2.5 in different periods by orthogonal matrix decomposition method（PMF）, which showed some meaningful results.（1）From 2013 to 2015, it showed obvious temporal and spatial distribution characteristics of PM2.5 in Lanzhou. The spatial distribution presented characteristics: industrial area > residents traffic mixed area > commercial and residential and traffic mixed area > residential area > suburban area; The time distribution of the interannual variation showed the trend of decreasing yearly, and the annual variation showed a typical bimodal curve, in which March and December reached a peak and December reached the highest value; A seasonal variation is winter > autumn > spring > summer.（2） During the period of source apportionment, PM2.5 pollution, which is particularly serious in the heating period, was at a high level in different periods（heating period, dust and non- heating non-dust periods） in Lanzhou, and PM2.5 surpassed the WHO and China’s air quality secondary standard. The total quality concentration of inorganic elements of PM2.5 in heating period and dust accounted for 1.50%11.27% and 1.83%20.93% of PM2.5 mass concentration; And water-soluble ion pollution characteristics of PM2.5 in different periods were basically the same, mainly including SO42-, NO3- and NH4+, accounting for 21.00%26.25% of PM2.5 mass concentration.（3） During the period of source apportionment, PM2.5 and its water-soluble ions had a significant positive correlation in Lanzhou, among which the SO42- and NH4+ had the strongest association（r=0.918）. What’s more, SO42-/NO3- was much higher than 0.125 in the three different periods, which strongly supports the view that secondary particle of PM2.5 are mainly from the stationary source emission during coal combustion.（4） PM2.5 sources are not the same in different periods in Lanzhou. The sources of heating period is mainly the mixed source of secondary sulfate, nitrate and biomass burning, contributing to 50.2%, while construction dust and vehicle exhaust ranked second. During the dust period, it was mainly for the construction dust, the contribution of 37.6%, followed by biomass burning and secondary sulfate and nitrate.In summary, it was in a relatively higher level of pollution of PM2.5 during different periods in Lanzhou, with Industrial area and the heating period being particularly serious, but which was decreasing overall; In different periods inorganic elements and water soluble ionic pollution characteristics of PM2.5 were basically the same, based on Al, Fe and SO42-, NO3- and NH4+; PM2.5 sources varied in different periods, in which was mainly secondary sulfate, nitrate and biomass burning mixed source in heating period, followed by construction dust in the dust period. |
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