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The observation of the nocturnal boundary layer height (NBLH) plays an important role in air pollution and monitoring. Through 39 d of heavy pollution observation experiments in Beijing (China), as well as an exhaustive evaluation of the gradient, wavelet covariance transform, and cubic root gradient methods, a novel algorithm based on the cluster analysis of the gradient method (CA-GM) of lidar signals is developed to capture the multilayer structure and achieve night-time stability. The CA-GM highlights its performance compared with radiosonde data, and the best correlation (0.85), weakest root-mean-square error (203 m), and an improved 25 % correlation coefficient are achieved via the GM. Compared with the 39 d experiments using other algorithms, reasonable parameter selection can help in distinguishing between layers with different properties, such as the cloud layer, elevated aerosol layers, and random noise. Consequently, the CA-GM can automatically address the uncertainty with multiple structures and obtain a stable NBLH with a high temporal resolution, which is expected to contribute to air pollution monitoring and climatology, as well as model verification. [ABSTRACT FROM AUTHOR]

• Seismic responses of the precast horseshoe segmental tunnel were tested. • Tunnel model segments were independently hardened and connected using model bolts. • The deformation and damage of the tunnel model were analyzed. • Higher order mode shapes of the soil-tunnel model system were characterized. A novel precast horseshoe segmental tunnel (PHST) structure was applied in the construction of the west extending project of Beijing Subway Line 6. The seismic performance of the PHST was one of the critical difficulties for the engineering project. A series of investigations were conducted to deal with the problem, including the 1-g shaking table model tests of the PHST buried in sand. In the present study, the experimental setup, construction of the PHST model (tube), dynamic properties of the soil-tube system, deformation mode and damage patterns of the tube were introduced. The preliminary results show that the tube had a very slight influence on the dynamic properties of the soil-tube system, which was consistent with the traditional learning. Under seismic motions with the precautionary intensity of the prototype site, the dynamic properties of the soil-tube system were not varied. The seismic responses of the tube were within the linear range. With the increasing seismic intensity, the predominant frequencies of the soil-tube system were firstly decreasing and then tended to be rather steady; meanwhile, the viscous damping ratio was firstly increasing and then rather steady. Under the excitations of the rare seismic motions, the non-linear responses of the tube were observed. The connection regions were damaged and tended to failures. Under the effects of the very rare motions, the thorough failures were observed at the connections. The tube was developed as a multi-hinge mechanism. The damage patterns at the connections were flexural damage and shear slide between segments. After the actions of strong motions, the tube kept horizontally expanding and vertically shrinking. [ABSTRACT FROM AUTHOR]

The types of aerosols are essential for estimating radiative forcing effects, improving the lidar retrieval algorithms, and identifying aerosol sources. However, it is difficult to categorize the aerosols with similar optical properties based on lidar techniques. In this study, an approach was proposed to distinguish desert dust (DD), mineral dust (MD), air pollution aerosols (APA), and their mixtures (DD&MD, DD&APA, MD&APA, DD&MD&APA). We established the fluorescence–Mie​ polarization lidar (FMPL) system to categorize three types of main aerosols using the customized fluorescence-to-Mie ratio (FMR) and volume depolarization ratio (VDR) in the experiments from September 2017 to December 2018. Then, the mixture of the aerosols was classified by combining backward trajectory analysis. The feasibility of this method was verified through five typical cases in the paper, and it is proved that the method could be employed to study air pollution issues based on FMPL, which could provide references for the meteorological investigation. • We established a fluorescence–Mie polarization lidar system. • We defined Fluorescence-to-Mie ratio (FMR). • Aerosols were divided into seven types according to their FMR and VDR. [ABSTRACT FROM AUTHOR]