Abstract
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 (PM2.5). Due to the lack of high-resolution vertical wind measurements, how the VWS affects ground-level PM2.5 remains highly debated. Here we employed the wind profiling observations from the fine-time-resolution radar wind profiler (RWP), together with hourly ground-level PM2.5 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 PM2.5 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 PM2.5 accumulation induced by weak vertical mixing in the PBL. Notably, weak northbound transboundary PM2.5 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 PM2.5, which deserves explicit consideration in the forecast of air quality in the future.
Highlights
The main findings are summarized as follows: Overall, the diurnal variations in wind profiles were found to differ greatly when classified by different ground-level PM2.5 concentrations
The southerly wind anomalies dominated throughout the whole planetary boundary layer (PBL) or even beyond the PBL under polluted conditions during the course of a day, in sharp contrast to the northerly wind anomalies in the PBL under clean condition
This favored the transboundary transport originated from significant aerosol emission source to the south of Beijing, thereby leading to high ground-level PM2.5 concentration in Beijing
Summary
Particulate particle with an aerodynamic diameter of 2.5 μm or less (PM2.5), mainly originated from industrial emissions and vehicle exhaust pollutants, and secondary aerosols forming through a series of photochemical reactions [1,2] have been shown to significantly affect the atmospheric environment [3,4,5], weather and climate system [6,7,8,9,10,11,12,13,14,15], and human health [16,17,18,19]. In addition to high emissions accompanied with the rapid development of urbanization and industrialization, the roles of meteorological conditions, including large-scale synoptic patterns [22,23,24,25,26], and local meteorological conditions in the planetary boundary layer (PBL) [27,28,29,30,31,32] have been well recognized able to modulate the PM2.5 concentration. In 68 major cities of China, ground-level PM2.5 were found to be broadly associated with local meteorological factors at seasonal, yearly, and regional scales [33]. The surface wind speed was one of the variables modulating ground-level PM2.5 over the Yangtze River Delta region of China, which showed that PM2.5 decreased approximately by -2.42 μg m−3 for a 1 m s−1 increase in wind speed [34]. The changes in circulation induced by local mountain-valley and urban heat island setting in Beijing and its surrounding areas were found to be able to modulate the diurnal variations of PM2.5 in Beijing [32]
Sign-in/Register to view highlights & summary 
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call