Yucong Miao

Compound events of extreme heat and ozone (O₃) pollution pose severe risks to public health in megacities. Using ground-based observations and chemical transport model simulations, we identified distinct synoptic patterns associated with hot-polluted versus cool-clean conditions in Shanghai during the summers of 2022-2025. Hot-polluted days were characterized by higher heat index (HI ≥ 41 °C), elevated O₃ (MDA8 ≥ 160 µg m^- 3), and southwesterly winds at 925 hPa. While anthropogenic NOx levels were comparable, biogenic volatile organic compound (BVOC) emissions from forests south of Shanghai increased significantly under high-temperature conditions. These BVOCs, transported by prevailing southwesterly winds, exacerbated O₃ formation downwind in Shanghai. Our findings highlight that regional biogenic emissions, amplified by extreme heat, are a critical driver of O₃ exceedances, complicating control strategies in the Yangtze River Delta.

Tangshan, a major industrial and agricultural center in northern China, frequently experiences significant PM_2.5 pollution events during winter, impacting its large population. These pollution episodes are influenced by multi–scale meteorological processes, though the complex mechanisms remain not fully understood. This study integrates surface PM_2.5 concentration data, ground-based and upper–air meteorological observations, and ERA5 reanalysis data from 2015 to 2019 to explore the interactions between local planetary boundary layer (PBL) structures and large-scale atmospheric processes driving PM_2.5 pollution in Tangshan. The results indicate that seasonal variations in PM_2.5 pollution levels are closely linked to changes in PBL thermal stability. During winter, day–to–day increases in PM_2.5 concentrations are often tied to atmospheric warming above 1500 m, as enhanced thermal inversions and reduced PBL heights lead to pollutant accumulation. Regionally, this aloft warming is driven by a high-pressure system at 850 hPa over the southern North China Plain, accompanied by prevailing southwesterly winds. Additionally, southwesterly winds within the PBL can transport pollutants from the adjacent Beijing–Tianjin–Hebei region to Tangshan, worsening pollution. Simulations from the chemical transport model indicate that regional pollutant transport can contribute to approximately half of the near-surface PM_2.5 concentration under the unfavorable synoptic conditions. These findings underscore the importance of multi-scale meteorology in predicting and mitigating severe wintertime PM_2.5 pollution in Tangshan and surrounding regions.

Urban surfaces exert profound influences on local wind patterns, turbulence dynamics, and the dispersion of air pollutants, underscoring the critical need for a thorough understanding of these processes in the realms of urban planning, design, construction, and air quality management. The advent of advanced computational capabilities has propelled the computational fluid dynamics model (CFD) into becoming a mature and widely adopted tool to investigate microscale meteorological phenomena in urban settings. This review provides a comprehensive overview of the current state of CFD-based microscale meteorological simulations, offering insights into their applications, influential factors, and challenges. Significant variables such as the aspect ratio of street canyons, building geometries, ambient wind directions, atmospheric boundary layer stabilities, and street tree configurations play crucial roles in influencing microscale physical processes and the dispersion of air pollutants. The integration of CFD with mesoscale meteorological models and cutting-edge machine learning techniques empowers high-resolution, precise simulations of urban meteorology, establishing a robust scientific basis for sustainable urban development, the mitigation of air pollution, and emergency response planning for hazardous substances. Nonetheless, the broader application of CFD in this domain introduces challenges in grid optimization, enhancing integration with mesoscale models, addressing data limitations, and simulating diverse weather conditions.

Editorial: Physical and chemical processes within the planetary boundary layer and their impacts on air pollution

The effects of aerosols on deep convective systems are highly uncertain. We used a coupled meteorology and chemistry model to investigate the effects of aerosols on a convective precipitation event that took place in North China from 7 to 10 October 2017. A higher concentration of aerosols can lead to more cloud condensation nuclei, which increases the condensation of water vapor and the formation of cloud droplets. Although the auto‐conversion from cloud droplets to rain can be inhibited due to the diminished effective radius of cloud droplets, more cloud droplets can be accreted by raindrops, resulting in a larger effective radius of raindrops and making them less likely to evaporate. Besides, aerosols can contribute to the vapor deposition of snow, and a larger number of cloud droplets can provide the resources needed for the riming growth of snow in the cloud, which eventually results in more and larger snow particles. Also, the net latent heat released by these microphysical processes can increase the vertical velocity and facilitate the development of the convective system. Thereby, the precipitation in North China during the study period was ultimately enhanced. We analyzed the influence of aerosols on this precipitation event from a microphysical perspective, which might improve our understanding of complex aerosol‐cloud‐precipitation interactions.

Heavy PM_2.5 (particulate matter with an aerodynamics diameter less than 2.5 μm) pollution frequently happens in Wuhan under unfavorable meteorological conditions. To comprehensively understand the complex impact of both regional-scale synoptic forcing and local-scale processes within the planetary boundary layer (PBL) on air quality in Wuhan, this study analyzed long-term PM_2.5 concentration measurement, near-surface and upper-air meteorological observations from March 2015 to February 2019, in combination with the Modern-Era Retrospective Analysis for Research and Applications version 2 (MERRA-2). We found that in winter the day-to-day change of PM_2.5 pollution level in Wuhan was governed by the synoptic warm/cold advection, in addition to the high emissions of pollutants. The synoptic condition can largely determine both the vertical development of PBL and horizontal transport of pollutants. When a high-pressure system is located to the north of Wuhan at the 900-hPa level, the induced warm advection above 1,000 m can enhance the thermal stability of lower troposphere and inhibit the development of daytime PBL, leading to a decreased dispersion volume for pollutants. Meanwhile, within the PBL the pollutants emitted from Henan, Shandong, and Anhui provinces can be transported to Wuhan, further worsening the pollution. Our results highlight the importance of coordinated pollution controls in Central China and adjacent north regions under the unfavorable synoptic condition.

Low‐level jets (LLJs) play important roles in the transport of heat, energy, moisture, and air pollutants. The climatic characteristics of the LLJ over China remain poorly investigated due to the lack of long‐term appropriate measurements. In this study, we obtained a climatology of LLJs over China using newly available, long‐term radiosonde observations from 2011 to 2017. We identified six regions in China with high‐frequency LLJs, which are centered in the Western Inner Mongolia, Yungui Plateau, and Huaihe River Basin, as well as Tarim Basin, Southeast Coast and Northeast Plain. The LLJ occurrence frequency ranged from 26.8% to 33.5%, with clear seasonal variation. LLJs were most frequent in spring and autumn in eastern China, in spring and summer in northwest China, and in autumn and winter along the Southeast Coast. LLJs were associated with stronger southwesterly winds on the Northeast Plain (∼17.0 m s⁻¹), but with weak northeasterly winds in the Tarim Basin and Southeast Coast (∼14 m s⁻¹). Most LLJs occurred at the heights of under the 500 m above the ground level excluding those on the Yungui Plateau. Seasonal changes in LLJ wind direction and height were observed in south China, i.e., higher southwesterly LLJs in summer and lower northeasterly LLJs in other seasons, which is attributed to seasonal variation in the summer and winter monsoons. The findings of this study will contribute to a better understanding of the development and effects of LLJs over China.