Determination and climatology of diurnal cycle of atmospheric mixing layer height over Beijing 2013–2018: Lidar measurements and implication for airpollution

2020 
Abstract. The atmospheric mixing layer height (MLH) determines the volume available for the dispersion of pollutants and thus contributes to the assessment of the pollutant concentration near the surface. The study evaluates the capability of lidar to describe the evolution of atmospheric mixing layer and then presents a long term observed climatology of MLH diurnal cycle. A system for automatic detection of the mixing layer height based on two wavelet methods (MLH and MLH') applied to lidar observations was operated from January 2013 to December 2018 in the Beijing urban area. The two dataset results are compared with radiosonde as case studies and statistical form. MLH shows good performance to calculate the convective layer height at daytime and the residual layer height at night. While MLH' has the potential to describe the stable layer height as radiosonde at night, the performance is limited due to the high range gate of lidar. A nearly six year climatology for diurnal cycle of MLH is calculated for convective and stable conditions using the dataset of MLH from lidar. The MLH characteristics of seasonal change in Beijing indicate that it is low in winter and autumn, and high in spring and summer. A significant phenomenon is found that from 2013 to 2018, the diurnal cycle of MLH increase year by year. It may partly benefit from the improvement of air quality. As to converting the column optical depth to the surface pollution, MLH from lidar shows better accuracy than that from radiosonde. Additionally, the accuracy with lidar MLH shows a diurnal cycle, with the peak at time of 14:00 LST. The study provides a significant dataset of MLH based on measurement and could be an effective reference to atmospheric models for surface air pollution calculation and analysis.
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