Vertical wind shear (VWS) is one of the key meteorological factors in modulating ground-level particulate matter with an aerodynamic diameter of 2.5 µm or less (PM_2.5). Due to the lack of high-resolution vertical wind measurements, how the VWS affects ground-level PM_2.5 remains highly debated. Here we employed the wind profiling observations from the fine-time-resolution radar wind profiler (RWP), together with hourly ground-level PM_2.5 measurements, to explore the wind features in the planetary boundary layer (PBL) and their association with aerosols in Beijing for the period from December 1, 2018, to February 28, 2019. Overall, southerly wind anomalies almost dominated throughout the whole PBL or even beyond the PBL under polluted conditions during the course of a day, as totally opposed to the northerly wind anomalies in the PBL under clean conditions. Besides, the ground-level PM_2.5 pollution exhibited a strong dependence on the VWS. A much weaker VWS was observed in the lower part of the PBL under polluted conditions, compared with that under clean conditions, which could be due to the strong ground-level PM_2.5 accumulation induced by weak vertical mixing in the PBL. Notably, weak northbound transboundary PM_2.5 pollution mainly appeared within the PBL, where relatively small VWS dominated. Above the PBL, strong northerlies winds also favored the long-range transport of aerosols, which in turn deteriorated the air quality in Beijing as well. This was well corroborated by the synoptic-scale circulation and backward trajectory analysis. Therefore, we argued here that not only the wind speed in the vertical but the VWS were important for the investigation of aerosol pollution formation mechanism in Beijing. Also, our findings offer wider insights into the role of VWS from RWP in modulating the variation of PM_2.5, which deserves explicit consideration in the forecast of air quality in the future.

This research systematically studied heavy rain that occurred on 5 August 2014 over the southeastern Tibetan Plateau (31°N–35°N, 96°E–103°E) using orbital data from the Tropical Rainfall Measuring Mission (TRMM) precipitation radar (PR), the TRMM Multi-satellite Precipitation Analysis (TMPA) products, and the European Centre for Medium-range Weather Forecast (ECMWF) Re-Analysis Interim reanalysis data (ERA-Interim). The data studied included spatial and temporal distributions of the precipitation; horizontal distributions and vertical structures of the precipitation system; convective storm top altitudes and types of rain; mean rainfall profiles; the influence of water vapor content before and after the rainfall; and the atmospheric circulation background. The results suggest that most precipitation on the Tibetan Plateau occurs in the southeast, and that the maximum near-surface precipitation rate for this event was more than 100 mm·h⁻¹. The convection was so powerful that the convective storm top altitude surpassed 16 km. Furthermore, the water vapor content caused obvious changes in the upper troposphere and lower stratosphere (UTLS) area. The mean rainfall profile can be roughly divided into four layers and showed that the maximum rainfall rate appeared at about 5.5 km. Deep weak precipitation provided the largest contribution to the total precipitation, while the highest average precipitation rate was from deep strong convective precipitation. The atmospheric circulation situation is conducive to the formation of strong convective weather, and the terrain is also an external factor affecting precipitation for this event.