Aerosol–planetary boundary layer (PBL) interaction has been proposed as a key mechanism for stabilizing the atmosphere and exacerbating surface air pollution. Although the understanding of this process has progressed enormously, its magnitude and impact remain uncertain and vary widely concerning aerosol types, vertical distributions, synoptic conditions, etc. In this study, our primary interest is to distinguish the aerosol–PBL interaction of absorbing and scattering aerosols under contrasting synoptic patterns and aerosol vertical distributions. Detailed in situ aircraft (King Air 350) measurements and online coupled model Weather Research and Forecasting with Chemistry (WRF-Chem) simulations are explored over the North China Plain (NCP). Furthermore, a long-term PBL stability trend from 1980 to 2020 over the NCP is also investigated. The aircraft measurements and surface observations show that the surface air pollution over the city of Baoding on 3 January is heavier than that on 4 January 2020. In addition, the aerosols are restricted to the low layer on 3 January, whereas the aerosols mix more homogeneously in an upwards direction on 4 January. Thus, we focus on the 2 d with distinct synoptic circumstances, PBL stability, and aerosol vertical distributions over the NCP. According to the WRF-Chem modeling, the synoptic pattern over Baoding differs between the 2 d. The prevailing wind direction is opposite with a southwesterly wind on 3 January and a northeasterly wind on 4 January. The results indicate that the synoptic condition may affect the PBL thermal structure, thus affecting the aerosol vertical distribution. Additionally, the sensitive numerical experiments reveal that the light-absorbing and light-scattering aerosols have different effects on altering the PBL thermal structure. The inhibition effect of scattering aerosols on the PBL appears to be independent of the aerosol height distribution and solely depends on its concentration. However, the aerosol–PBL feedback of absorbing aerosols is highly dependent on its vertical distribution. Besides the 2 d case investigation, the analysis of the modeling results for nearly 1 month from 3 to 30 January 2020 in Baoding yields a more robust and representative conclusion. Our analysis highlights that we should principally concentrate on controlling the emissions of scattering aerosols under the stable stratification, while cooperating to control the emissions of scattering and absorbing aerosols in an unstable stratification. Moreover, the long-term interannual variation in the PBL stability shows a strong correlation with the East Asian winter monsoon, which seems to be valuable in determining which pollutants to target in different monsoon years and attaining more precise air pollution control. Based on the numerical simulations and observational constraints, a concept scheme description has been concluded to deepen our recognition of the interactions between thermodynamic stability and aerosols within the PBL over the NCP region.

Severe hailstorms frequently occurred in Beijing between May and August 2021, leading to extensive hail damage. These hailstorms were observed by radar and satellite data, and reported by surface observers. In this study, the spectral and cloud microphysical characteristics of typical Beijing events in 2021 were analyzed using Himawari-8 satellite products and ground-based S-band weather radar data obtained from the Beijing Meteorological Bureau. The relationship between Himawari-8 brightness temperature differences (BTD) and radar reflectivity was also investigated. The results revealed that the significant spectral depression of brightness temperatures (BTs) in hail clouds was observed by a satellite. Furthermore, the stronger the radar reflectivity was, the more rapidly BTD decreased, with a nonlinear relationship between them. The results of cloud physical characteristics show that, for cloud-top heights above 10 km, the cloud effective radius was about 25 μm, with a cloud-top temperature of 225 K during these hail events. By means of Gaussian fitting, the BT threshold value (11.2 μm) was determined by satellite at 230 K, with a BTD focused on 1.9 K when hailstorms occurred. These results will help us better understand the characteristics of hailstorms, while also providing information for future hail suppression in Beijing.

There are few studies which reported the characteristics of winter clouds and precipitation in the Haituo Mountains of Northern Beijing where the 2022 Winter Olympic Games will be held. This paper outlines comprehensive datasets, including the surface measurements, remote sensing and aircraft measurements, to study cloud and precipitation characteristics over the mountainous terrain. The analysis results show (1) high-level trough and vortex were the main weather system in all 12 cases. (2) 58% of precipitation occurred only at night, and only 8% of snowfall occurred only at daytime, but under the surface inverse trough snowfall (in 4 of the 12 cases) persisted from night to day peaking at 20 hours; Snowfall persisted at least 3 hours in 83% of the snowfall, 5–10 hours in 50% of cases, and more than 10 hours in 33% of the storms. In 67% of cases, the maximum snowfall occurred within the initial 1-2 hours. (3) In 12 cases, 83% of orographic clouds reached Yan Jiaping, after increased southwesterly winds, resulting in visibility below 100 m. (4) during snowfall, The dominant wind direction is southwest. The start of the snowfall corresponded with an increase in southwesterly wind. The snowfall is maintained according to with the strengthening of southwesterly wind and dissipated accordingly with the receding of southwesterly wind. Whenever the snowfall stopped, the northwest wind was strong at all heights. (5) The first peak value of integral liquid water appeared in the early stage of snow, and we also observed integral liquid water increases with orographic cloud uplift, presenting potentially favorable seeding opportunities in 10 cases. (6) The primary crystal habits collected at Yan Jiaping during steady snowfall were rimed and aggregated planar dendrites.