Abstract:Temporal and spatial variations of haze days in four seasons and dominant factors are analyzed based on meteorological data from 51 surface weather stations in Liaoning Province between 1961 and 2020. The results show that the annual haze days averaged in Liaoning Province have a significant increasing trend of 2.1 d per decade from 1961 to 2020 and a decreasing from 2015 to 2020. In terms of spatial distribution, there is a high value center (Shenyang) and two sub high value centers (Jinzhou and Beipiao), where the annual haze days are respectively 139 d, 52 d and 46 d. Comparatively, the annual haze days in the mountain areas of western and eastern in Liaoning Province are the least, less than 20 days on average. Wind direction and wind speed are important meteorological factors for the formation of haze. The warm and humid air brought by the increase of south southwesterly winds has a greater contribution to haze formation in spring, summer and autumn, while the decrease of northerly winds helps the formation of haze days in winter. The frequencies of south southwest winds in spring, summer and autumn have increased from 11.4%, 12.1% and 8.0% to 15.8%, 19.8% and 13.5%, respectively. When haze occurs, the wind speeds in all four seasons are lower than the average, indicating that light wind is conducive to the formation of haze. The long term evolution of haze in Liaoning Province is affected by pollutant emissions, wind factors and environment manage policies. The growth of haze days from 1980 to 2003 was caused by the increased pollutants and decreased wind speeds. The reduction of haze days since 2015 is very likely related to the reduction of PM2.5, which is achieved by air pollution control. At the same time, fewer light wind days also provide a favorable meteorological condition for the reduction of haze days.