2015-2019年兰州市两区大气细颗粒物及其化学成分变化趋势

目的 分析兰州市两区2015-2019年大气细颗粒物(fine particulate matter,PM2.5)浓度及其化学成分变化趋势.方法 于2015年1月至2019年12月在兰州市选择住宅区代表城关区和工业区代表西固区2个采样点,采集大气细颗粒物样品,检测其质量浓度、金属和类金属元素、水溶性离子及多环芳烃(po...

Trend of atmosphreic PM2.5 and their components in two districts of Lanzhou City from 2015 to 2019

OBJECTIVE To analyse the variation of the fine particulate matter(PM2.5) concentration and its chemical composition in two districts of Lanzhou City from 2015 to 2019. METHODS From January 2015 to December 2019, two sampling points, namely residential district(Chengguan District) and industrial district(Xigu District) were selected in Lanzhou City, to collect PM2.5 samples, and the mass concentrations, metals and metalloid elements, water-soluble ions and polycyclic aromatic hydrocarbons(PAHs) contents were determined. RESULTS A total of 838 samples were collected in Chengguan District and Xigu District in Lanzhou City during 2015-2019,the average annual mass concentration and the daily average concentration of the PM2.5 were decreasing year by year(P<0.05).The higher metal content in PM2.5 were Al, Pb, Mn and As during 2015-2019.Sb, Al, As, Cd, Cr, Pb, Mn and Tl element content were higher in 2015 and 2016 than in other years(P<0.05), the average annual concentration of As were 7.92 and 8.63 ng/m3 respectively, which exceeded the reference concentration limit of the ambient air quality standard. The average annual mass concentration of Cr from 2015 to 2019 was much higher than the annual average reference concentration limit of the ambient air quality standard. From 2015 to 2019, except for 2018, the highest average concentration of PAHs in atmospheric PM2.5 in the two districts of Lanzhou City was Ant, B(b)F and I(cd)P mass concentration were highest in 2015, N(a)P,FI,Ace, Phe, Ant, Flu, Pyr, B(k)F and B(a)P mass concentration were highest in 2017, Acy, Chr and B(ghi)P mass concentration were highest in 2018(P<0.05). From 2017 to 2018, the average annual content of B(a)P in the two districts of Lanzhou City were 1.16 and 1.11 ng/m3, respectively, which exceeded the annual average concentration limit of the ambient air quality standard. The concentration of Cl- in PM2.5 in the two districts of Lanzhou City was decreasing year by year, the annual average concentrations of SO■, NO-3 and NH+4 from 2017 to 2019 showed a downward trend year by year.SO■,Cl- of both districts were the highest in 2015, and NO-3,NH+4 were the highest in 2017(P<0.05). CONCLUSION The air quality of Lanzhou City has been improved obviously, but the pollution problem is still serious.