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Abstract Soil heat flux plates (SHFPs) are widely used to measure soil heat flux (Gs). Gs is often underestimated by SHFPs (Gp). Although calibration methods are used, they are not always effective. The objective of this study is to evaluate the effectiveness of a field calibration method applied to various SHFPs installed in a full canopy maize field. A 5‐day measurement period with wet and dry soil conditions was used for calibration, while 80‐day and 60‐day measurement periods were used for evaluation. Uncorrected SHFP measured values (Gp) underestimated the actual reference Gs determined by the gradient method (Gs_grad) by 42%–64%. Gp values in the evaluation period were corrected (Gp_corr) by dividing them by the ratio of Gp/Gs_grad determined over the calibration period. After the correction, the Gp_corr agreed well with the Gs_grad, with Gp_corr/Gs_grad of four of six SHFPs being 0.90–1.01, improving to 74%–98%. The field calibration performed approximately the same with the wet and dry calibration periods, whether the calibration and evaluation periods were consecutive in time or had relatively long time intervals, indicating that this method accounted for almost all errors with SHFP. This is largely due to the slight variation in soil thermal conductivity and the linearity between soil temperature gradients from SHFP and the gradient method under relatively stable soil moisture conditions. This study deepens our understanding and improves the accuracy of soil heat flux measurements. Calibration of SHFPs under various land covers and weather conditions is warranted in future studies. 

Abstract Aerosol-boundary layer interactions play an important role in affecting atmospheric thermodynamics and air pollution. As a key factor in dictating the development of the boundary layer, the entrainment process in the context of aerosol-boundary layer interactions is still poorly understood. Using comprehensive field observations made at a superstation in Beijing, we gain insight into the response of the entrainment process to aerosols. We found that high aerosol loading can significantly suppress the entrainment rate, breaking the conventional linear relationship between sensible heat fluxes and entrainment fluxes. Related to aerosol vertical distributions, aerosol heating effects can alter vertical heat fluxes, leading to a strong interaction between aerosols and the entrainment process in the upper boundary layer. Such aerosol-entrainment coupling can inhibit boundary layer development and explains the great sensitivity of observed entrainment rates to aerosols than can traditional calculations. The notable impact of aerosols on the entrainment process raises holistic thinking about the dynamic framework of the boundary layer in a polluted atmosphere, which may have a significant bearing on the dispersion of air pollutants and the land-atmosphere coupling. 

Abstract. The aerosol–planetary boundary layer (PBL) interaction wasproposed as an important mechanism to stabilize the atmosphere andexacerbate surface air pollution. Despite the tremendous progress made inunderstanding this process, its magnitude and significance still have largeuncertainties and vary largely with aerosol distribution and meteorologicalconditions. In this study, we focus on the role of aerosol verticaldistribution in thermodynamic stability and PBL development by jointly usingmicropulse lidar, sun photometer, and radiosonde measurements taken inBeijing. Despite the complexity of aerosol vertical distributions,cloud-free aerosol structures can be largely classified into three types:well-mixed, decreasing with height, and inverse structures. The aerosol–PBLrelationship and diurnal cycles of the PBL height and PM2.5 associated with these different aerosol vertical structures showdistinct characteristics. The vertical distribution of aerosol radiativeforcing differs drastically among the three types, with strong heating in thelower, middle, and upper PBL, respectively. Such a discrepancy in the heatingrate affects the atmospheric buoyancy and stability differently in the threedistinct aerosol structures. Absorbing aerosols have a weaker effect ofstabilizing the lower atmosphere under the decreasing structure than underthe inverse structure. As a result, the aerosol–PBL interaction can bestrengthened by the inverse aerosol structure and can be potentiallyneutralized by the decreasing structure. Moreover, aerosols can both enhanceand suppress PBL stability, leading to both positive and negativefeedback loops. This study attempts to improve our understanding of theaerosol–PBL interaction, showing the importance of the observationalconstraint of aerosol vertical distribution for simulating this interactionand consequent feedbacks.