Concentration changes of ten metal and metalloid elements in atmospheric PM_(2. 5) in two districts of Lanzhou City from 2015 to 2018

OBJECTIVE To detect the concentrations of ten metals and metalloid elements in the atmospheric PM_(2. 5) in Chengguan district and Xigu district of Lanzhou City from 2015 to 2018, and analyze the pollutant concentration and its change trend. METHODS From 2015 to 2018, 662 samples of PM_(2. 5) were collected from Chengguan district and Xigu district of Lanzhou City. The concentrations of 10 kinds of metals and metalloid elements such as lead(Pb), arsenic(As), mercury(Hg), cadmium(Cd), chromium(Cr), antimony(Sb), manganese(Mn), nickel(Ni), selenium(Se), beryllium(Be) were detected, and the change trends of different monitoring points, years, seasons and months were analyzed. RESULTS There was a significant difference in lead content between Chengguan District and Xigu District(χ~2=4. 80, P 0. 05). From 2015 to 2018, the element content of PM_(2. 5) in Chengguan District decreased by 47. 66% compared with 2015; Xigu District in 2018 decreased by 43. 79% compared with 2015; the higher element Pb, Mn and As in Chengguan District decreased by 52. 93%, 47. 00% and 49. 37% compared with 2015; in Xigu District, the content in 2018 decreased by 46. 87%, 47. 49% and 41. 98%compared with 2015, the contents of the remaining seven elements decreased in 2018 compared with those in 2015. There was no statistical significance(P>0. 05) in different seasons except for the difference of Ni content(P spring>autumn> summer. The trend of monthly concentration change in the two regions was basically the same, the concentrations of Sb, As, Pb, Mn, Cd, Ni, Se, Hg and Cr were higher in November and February of next year. In Chengguan District and Xigu District, Ni content was higher in July and August, respectively;and Hg in Xigu District was higher in June, and Be was higher in less months, especially in February, October and December. CONCLUSION From 2015 to 2018, the levels of 10 metals and metalloids element pollutants in PM_(2. 5) samples from Chengguan District and Xigu District of Lanzhou City showed a decreasing trend year by year, and had obvious seasonal changes.