[Analysis of polycyclic aromatic hydrocarbons pollution characteristics in PM_(2. 5) in two districts of Xi'an City from 2016 to 2018].

To analyze the pollution characteristics of polycyclic aromatic hydrocarbons(PAHs) in atmospheric PM_(2. 5) in Lianhu district and Yanta district of Xi'an City.From 2016-2018, PM_(2. 5) samples were regularly collected at monitoring points in two districts of Xi'an City, and analyzed the content of naphthalene, acenaphthylene, fluorene, acenaphthene, phenanthrene, anthracene, fluoranthene, pyrene, chrysene, benz(a)anthracene, benzo(b)fluoranthene, benzo(k)fluoranthene, benzo(a)pyrene, dibenz(a, h)anthracene, benzo(g, h, i)perylene, indeno(1, 2, 3-cd)pyrene in the samples according to Ambient air and stationary source emissions-Determination of gas and particle-phase polycyclic aromatic hydrocarbons-High performance liquid chromatography(HJ 647-2013). The test result were analyzed and evaluated according to different years, regions and seasons.The median total PAHs mass concentrations(ΣPAHs) in Lianhu district and Yanta district were 11. 68 and 12. 53 ng/m~3, respectively, with no significant difference(P>0. 05). The ΣPAHs of the two districts were decreasing year by year(P<0. 05). The median ΣPAHs in Lianhu district and Yanta district were highest in winter(55. 50, 55. 61 ng/m~3) and lowest in summer(4. 62, 4. 57 ng/m~3). The top three single indicators of the median PAHs in Lianhu district were benz(b)fluoranthene(1. 90 ng/m~3), benzo(g, h, i)perylene(1. 67 ng/m~3) and chrysene(1. 34 ng/m~3), In Yanta district, they were benz(b)fluoranthene(1. 95 ng/m~3), benzo(g, h, i)perylene(1. 63 ng/m~3) and pyrene(1. 47 ng/m~3). The average mass concentrations of benzo(a)pyrene in Lianhu district and Yanta district were 1. 33 ng/m~3 and 1. 10 ng/m~3, respectively. Among all the samples, the qualified samples of benzo(a)pyrene accounted for 72. 75% of the total samples, and the Lianhu district and Yanta district were 71. 20% and 74. 30%, respectively(P>0. 05).The degree of atmospheric PAHs pollution in Xi'an had decreased year by year, and PAHs pollution in winter was more serious.