A new method to retrieve PBLH from lidar under different thermodynamic conditions: algorithm development and application

The planetary boundary layer height (PBLH) is an important parameter for understanding the accumulation of pollutants and the dynamics of the lower atmosphere. In our study, we developed a new lidar-based PBLH algorithm and applied it to air quality pollution studies using long-term datasets of micropulse lidar (MPL) and radiosonde (RS) measurements at several superstations (Southern Great Plain, GSFC, and Beijing). The new method combines lidar-measured aerosol backscatter with a stability dependent model of PBLH temporal variation based on radiosonde data in the morning. The latter helps "recalibrate" the PBLH in the presence of a residual aerosol layer that does not change in harmony with PBL diurnal variation. The hybrid method offers significantly improved PBLH detection, with much better accuracy under most thermodynamic conditions. Built upon the physical process of PBL diurnal development, different schemes are developed for growing, maintenance, and decaying periods of PBL. Comprehensive evaluations of this new method shows much better capability in tracking the diurnal variation of PBL with significantly smaller biases under various pollution levels.

By utilizing the new PBLH algorithm along with sun photometer and RS measurements, we investigate the impacts of aerosol on thermodynamic stability and PBL development. Despite complex aerosol vertical distributions, the cloud-free aerosol structures can be classified into three types: well-mixed, decreasing and increasing (inversion) with height. Under different aerosol vertical structures, the aerosol-PBL relationships and the diurnal cycles of the PBLH and PM_2.5 show distinct characters. The vertical distributions of aerosol radiative forcing differ drastically, and thus, lead to different aerosol effects on the atmospheric buoyancy and stability. Absorbing aerosols have a much weaker effect in stabilizing the low-atmosphere under the decreasing structure than under the inversion structure. As a result, the aerosol-PBL interaction can be strengthened by the inversed aerosol structure and neutralized by the decreasing structure.