| 03 Jul 2026
Influence of irradiance and mixing layer height on the vertical trace matter distribution in the lower planetary boundary layer – drone-based investigation
Abstract. Drone-based atmospheric measurements allow time-resolved investigation of stratification in the lower atmosphere of many atmospherically relevant variables. Measuring a variety of variables can be used, e.g., for mixing layer (height, MLH) identification and examination of the representativity of ground-based measurements in the lowermost boundary layer. We present drone-based vertical profiling during two 2.5‑week summer field campaigns in rural Germany to investigate the vertical distribution of trace matter and meteorological variables in the lowermost troposphere.
Night-time vertical profiling of temperature, humidity, wind speed, and trace substances (CO2, O3, particle mass and number concentrations) in the lowest 120 m revealed a multiple-layer fine-scale stratification. Trace substances surpassed several traditional meteorological variables in sensitivity for MLH detection. Among all variables, O3 and potential temperature were the most reliable MLH markers, highlighting combining trace matter and meteorological measurements to understand stratification processes.
Using a gradient-based approach for diurnal vertical profiles up to 500 m above ground, we evaluate under which conditions and to which degree ground-based measurements, used world-wide in networks or during individual field campaigns, can be taken as representative for the lowermost mixing layer, and how strong radiative-driven mixing reduces vertical gradients. Location-specific sources and sinks affect the trace matter distribution in the ML much stronger than irradiance. However, homogeneity of aerosol particle concentrations was strongly promoted under high-radiative conditions, even at low MLHs. This suggests distinguishing between high- and low-irradiation conditions in the planetary boundary layer could improve parameterization for vertical mixing and should be considered when evaluating ground-based data.
This study (egusphere-2026-2494) investigates how irradiance and mixing layer height (MLH) affect the vertical distribution of trace substances in rural areas of Germany, using data from two summer drone measurement campaigns conducted up to 500 m above ground, along with data from ground-based stations. The findings suggest that irradiance is the primary factor influencing diurnal mixing mechanisms. Furthermore, the research highlights that ground-based measurements do not always accurately represent the conditions throughout the entire mixed layer. However, several concerns need to be addressed.
Thermal PBL height defined by static stability, e.g., potential-temperature or virtual-potential-temperature gradients/parcel method.
Dynamic PBL height defined by dynamic stability, e.g., bulk Richardson number or wind-shear criteria
Material PBL height, defined by the vertical distribution of atmospheric constituents, e.g., aerosol or trace gas gradients.
The three heights mentioned are not interchangeable; they correspond to distinct physical processes and often differ, particularly when there is weak dynamical forcing or when residual-layer chemistry and surface sources or sinks are present. The current manuscript fails to adequately recognize or discuss this important distinction. The authors should explicitly define and consistently distinguish thermal, dynamic, and material boundary-layer heights throughout the text, figures, and captions. The authors should also clarify why differences among the three methods are inevitable, focusing on the physical mechanisms involved instead of suggesting that one of the measured MLH values is a more accurate or comprehensive representation of MLH.
References
Tan, Y., Xin, J., Qin, X., Ma, Y., Xu, J., Du, Y., Shang, C., Zhao, L., Tian, Y., Fan, Q., Zhou, X., Ren, Y., Wang, P., Hao, F., Yin, N., Ren, X., Peng, K., Jia, D., Pan, X., Li, J., Wang, Z., and Butt, A. Q.: Differences Among Thermal, Dynamic, and Material Boundary Layers Over Complex Terrain, J. Geophys. Res., 130, e2024JD043043, doi: https://doi.org/10.1029/2024JD043043, 2025.