Objective: To master the variation characteristics of PM_(2. 5) mass concentration in Lianhu district and Yanta district of Xi'an City and its relationship with meteorological conditions.
Methods: From 2015 to 2018, according to the environmental monitoring data of six main urban areas in Xi'an City in 2012, including NO_2, SO_2, PM_(10), PM_(2. 5), CO and O_3, air samples were collected in the relatively heavy polluted Lianhu district and the relatively light Yanta district of Xi'an City. The mass concentration test of PM_(2. 5) was carried out in accordance with the Ministry of Environmental Protection's "Determination of atmospheric articles PM_(10) and PM_(2. 5) in ambient air by gravimetric method "(HJ 618-2011). According to the Ambient air quality standards(GB 3095-2012), the average daily secondary concentration limit(75 μg/m~3) was used for statistical analysis and evaluation according to different annual, regional and seasonal test result. Meteorological data of Xi'an City were collected, including daily average temperature, daily average pressure, daily average relative humidity, daily average wind speed, daily precipitation, maximum temperature and minimum temperature, and the relationship between PM_(2. 5)concentration and meteorological factors was analyzed.
Results: A total of 660 air samples were collected and qualified, the median concentration of PM_(2. 5) was 71 μg/m~3. 356 air samples were qualified, and the pass rate was 53. 94%. The sample pass rate for each year from high to low was 2017>2018>2016>2015(P<0. 001), The average level of PM_(2. 5) mass concentration from high to low was 2015>2016>2017>2018(P<0. 001). There was no significant difference in the sample pass rate and PM_(2. 5)mass concentration between Lianhu district and Yanta district(P>0. 05). The qualified rate of samples from high to low in different seasons was summer>spring> autumn>winter(P<0. 05). The average concentration of PM_(2. 5) in different seasons from high to low was winter>autumn>spring>summer(P<0. 001). Mean temperature, mean air pressure, average wind speed, average relative humidity, precipitation and lowest temperature were significantly correlated with PM_(2. 5) mass concentration(P<0. 001). The determination coefficients of multiple regression analysis of meteorological factors in Lianhu and Yanta regions were 0. 390 and 0. 373, respectively.
Conclusion: The air quality in Lianhu district and Yanta district of Xi'an City had improved year by year, and the pollution of PM_(2. 5) in autumn and winter was more serious. Meteorological conditions affected the concentration level of PM_(2. 5) in the atmosphere.
Keywords: PM_(2. 5); air quality; meteorological factor; multiple linear regression.