Variation Characteristics of the Atmospheric Mixed Layer Height and Their Telation to the Air Pollution in Yinchuan

Based on the high L-band second-level and ground observation data from the Yinchuan high-altitude station from 2008 to 2017, the time-divided atmospheric mixed layer height (MLH) was calculated for that time period using the dry adiabatic method, and its variation characteristics were analyzed. Simultaneously, the six pollutants in Yinchuan were used for the analysis. The mass concentration and air quality index (AQI) were used to determine the correlation between the atmospheric MLH and air pollutants. The results indicated that the majority of the MLH in Yinchuan was below 600 m, accounting for 68% of the total. Yinchuan MLH has a distinct single-peak diurnal variation, with the lowest at 0700 LST in the morning and the highest at 1600 LST in the evening. The monthly MLH values ranged from 282 m to 936 m; MLH values were the highest from April to June, with the lowest values in December. Furthermore, seasonal changes were the highest in spring, followed by summer and winter. Considering the annual changes, the highest average MLH was 621 m in 2012, and the lowest was 566 m in 2015. In addition to O₃, the concentrations of the rest five pollutants in Yinchuan are negatively correlated with the MLH value, with the best correlation being between O₃ and MLH values. Moreover, the best correlation was found between the winter pollutant concentration, and the MLH value was the best in winter, followed by autumn, spring, and worst in summer. The Yinchuan MLH value was negatively correlated to the AQI index of the city.