Atmosphere boundary layer height and its effect on air pollutants in Beijing during winter heavy pollution

Beijing is suffering from serious particulate matter pollution, and the atmosphere boundary layer (ABL) has important direct and indirect effects on human activities. This research analyzed the characteristics of the ABL in Beijing and discussed the impacts of meteorological factors on atmosphere boundary layer height (ABLH) during winter heavy pollution events in Beijing. The data observed by Mie lidar in the winter of 2014 to 2016 were used to estimate the ABLH by employing image edge detection. In addition, a weather research and forecasting (WRF) model was used to simulate the meteorological field in the same period. Ground and vertical data indicated that the average ABLH decreased from 0.63 km to 0.53 km in three consecutive years. In addition, a significant negative correlation existed between ABLH and PM_2.5, and the effect of low ABLH on the vertical diffusion capacity of pollutants was greater than that of high ABLH. Relative humidity was negatively correlated with ABLH, increasing during the three years at a rate of 61%. In the winter of 2014, the atmosphere was dominated by instability, which was beneficial to the development of ABL. In contrast, many stable stratifications occurred in the upper air during the winters of 2015 and 2016; however, these were not conducive to the development of ABL. The northwest wind decreased by 11.35% and the south wind increased by 11.41%. Moreover, the time of near-surface wind speed below 2 m s^-1 increased by 34.74%, and the frequency of occurrence above 4 m s^-1 decreased by 8.19%. The decrease in ground wind speed was unfavorable for the development of ABL. The sea level pressure remained at 1027.68 ± 17.32 hPa, and the ABLH was found to be generally positively correlated with sea level pressure.