Abstract
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 (KingAir-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 Baoding City 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 homogeneous upwards on 4 January. Thereupon, we focus on the two days with distinct synoptic circumstances, PBL stability, and aerosol vertical distributions over the NCP. According to the WRF-Chem modelling, the synoptic pattern over the Baoding City differs between the two days. The prevailing wind direction is opposite with a southwest wind on 3 January and a northeast 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, aerosol-PBL feedback of absorbing aerosols is highly dependent on its vertical distribution. 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 inter-annual variation in 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.
Highlights
Ambient air pollution has been one of the major environmental issues in China, in the highly populated and industrialized areas, such as the North China Plain (NCP) (Chan and Yao, 2008; Sun et al, 2014; Zhang, Q., Zheng, Y. et al., 2019a; Fan et al, 2020; Luo et al, 2021)
The accuracy of simulation during the daytime is superior to that at night, which is instrumental in the intention of discussing the planetary boundary layer (PBL) thermodynamic stability and aerosol radiative effect (ARE) in the daytime
The complex relationships between large-scale synoptic patterns, local PBL thermal structures, aerosol vertical distributions, and AREs of different aerosol types are systematically investigated by the combined aircraft observations, surface measurements, reanalysis data, and WRF-Chem simulations
Summary
Ambient air pollution has been one of the major environmental issues in China, in the highly populated and industrialized areas, such as the North China Plain (NCP) (Chan and Yao, 2008; Sun et al, 2014; Zhang, Q., Zheng, Y. et al., 2019a; Fan et al, 2020; Luo et al, 2021). The interaction of aerosols with the planetary boundary layer (PBL), which is regarded to be a critical process for stabilizing the atmosphere and worsening surface air pollution, has been widely explored in the context of aerosol weather and climate effects (Li, Z. et al, 2017a; Su et al, 2020; Hung et al, 2021). Despite the great progress in observational and numerical studies of ARI and ACI over the recent decades, correctly quantifying the aerosol radiative effect (ARE) on the weather and climate systems remains a challenge. The principal reason for this challenge is the inadequate understanding of strong variations in aerosol types, 55 loadings, and vertical distributions, as well as the complex mechanisms among large-scale synoptic patterns, local-scale planetary boundary layer (PBL) structures and AREs (Wang, H. et al, 2015; Li, Z. et al, 2017a; Huang et al, 2018; Su et al., 2020)
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