This study investigated the impact of atmospheric circulation and meteorological parameters on surface atmospheric extinction coefficient (SEC) in Chengdu and Chongqing of southwest China during the wintertime of 2001–2016. Four predominant circulation types (CT) were first identified representing high pressure system in the north (CT 1), low pressure system in the north (CT 2), weak high pressure system (CT 3) and local low pressure system (CT 4) at 850 hPa geopotential height. In Chengdu the between-CT variations of SEC were dominated by meteorological factors such as wind, subsidence, inversion and PBLH. While the within-CT variations were mainly controlled by dispersion-related parameters such as wind speed and PBLH in CTs with strong weather systems (CTs 1, 2 and 4) and chemical-related parameters such as RH and T in a CT with weak system (CT 3). In Chongqing dispersion and chemical processes were equally important due to the weaker impact of atmospheric circulation. A new method for discriminating the synoptic signals from non-synoptic ones in SEC time series was proposed to estimate the impact of atmospheric circulation intensity by considering multiple influencing meteorological parameters. Atmospheric circulation intensified inter-annual SEC variations by around 23 % in both Chengdu and Chongqing in more than half of the years and weakened such variations by 44.79 % in Chengdu and 8.02 % in Chongqing in the other years. Synoptic changes were estimated to contribute 5-10% of the decreasing trend of SEC and less than 1% of the increasing trend of SEC.