Abstract: Aim to find out the variation characteristics of atmospheric stability and mixed layer thickness in the slightly polluted area, based on the surface meteorological observation data of Tunxi and Mount Huangshan, Anhui Province, China at 02:00, 08:00, 14:00, and 20:00(Beijing Standard Time) from 2005 to 2014, the atmospheric stability and mixed layer thickness were calculated according to the national standard GB/T 3840-91. According to the modified Pasquill stability classification method, atmosphere stability was divided into 3 levels:instability, neutral and stability, and then mixed layer thickness was calculated according to the formula of different atmosphere stability grade. The results show as follows:(1) the highest occurrence frequency of atmospheric stability from 2005 to 2013 in both Tunxi and Mount Huangshan mainly belonged to the neutral category; meanwhile, the frequency of the neutral category in Mount Huangshan was higher than that in Tunxi. In recent years, there has been an increasing trend in the amplitude of the atmospheric stability frequency curve. The frequency of the neutral category in summer and winter was higher than that in spring and autumn, and the curve of the instability category represented opposite tendency. The variation characteristics in Tunxi were the same as those in Mount Huangshan, except for some differences in summer. Daily variation characteristics in Tunxi and Mount Huangshan exhibit that atmospheric stratification was mostly neutral in the morning, while the instability stratification increased at noon and the stability stratification increased at night.(2) The mean value of mixed layer thickness from 2005 to 2013 in Mount Huangshan was 2.7 times more than that in Tunxi. Annual mean value of mixed layer thickness reduced from 2005 to 2013, warning us that the trend of the atmospheric vertical dilution ability was weakened. There was a good correlation between the monthly mean value of mixed layer thickness and the monthly mean value of wind velocity. The daily mean value of mixed layer thickness in Tunxi reached the highest in the afternoon, and the daily variation curve of mixed layer thickness in Mount Huangshan was relatively stable.

Key words: Tunxi, Mount Huangshan, atmospheric stability, mixed layer thickness, wind speed, turbulence