Aerosol particles are important for radiation effects, cloud formation, and therefore the climate system. A detailed understanding of the spatial distribution of aerosol particles within the atmospheric boundary layer, which depends on sources and sinks, as well as long-range transport and vertical exchange, is important. Especially in marine regions, where the climate effect of clouds is comparably high, long-range transport with subsequent vertical mixing dominates over local aerosol sources.In this study, three different methods were applied to estimate the vertical aerosol particle flux in the marine boundary layer (MBL) and the vertical exchange between the MBL and the free troposphere (FT): eddy covariance (EC), flux–gradient similarity (K theory), and the mixed-layer gradient method (MLG). For the first time, MBL aerosol fluxes derived from these three methods were compared in the framework of the “Azores Stratocumulus Measurements of Radiation, Turbulence and Aerosols” (ACORES) field campaign in the Azores region in the northeastern Atlantic Ocean in July 2017. Meteorological parameters and aerosol and cloud properties were measured in the marine troposphere using the helicopter-borne measurement platform ACTOS (Airborne Cloud Turbulence Observation System).All three methods were applied to estimate the net particle exchange between MBL and FT. In many cases, the entrainment fluxes of the MLG method agreed within the range of uncertainty with the EC and K-theory flux estimates close to the top of the MBL, while the surface flux estimates of the different methods diverged. It was not possible to measure directly above the surface with the helicopter-borne payload, which might be a source of uncertainty in the surface fluxes. The observed particle fluxes at the top of the MBL ranged from 0 to 10×10⁶ m⁻² s⁻¹ both in the upward and the downward direction, and the associated uncertainties were on the same order of magnitude. Even though the uncertainties of all three methods are considerable, the results of this study contribute to an improved understanding of the transport of particles between the MBL and FT and their distribution in the MBL.

中文翻译：

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根据亚速尔群岛直升机载测量估计的海洋边界层垂直气溶胶粒子交换

气溶胶颗粒对辐射效应、云的形成以及气候系统都很重要。详细了解大气边界层内气溶胶颗粒的空间分布，这取决于源和汇以及远程传输和垂直交换，这一点很重要。特别是在海洋区域，云的气候效应相对较高，远程传输和随后的垂直混合在局部气溶胶源中占主导地位。在这项研究中，应用了三种不同的方法来估计海洋边界层中的垂直气溶胶粒子通量(MBL) 以及 MBL 与自由对流层 (FT) 之间的垂直交换：涡度协方差 (EC)、通量梯度相似度 ( K 理论）和混合层梯度法（MLG）。2017 年 7 月在大西洋东北部亚速尔群岛地区开展的“亚速尔群岛层积云辐射、湍流和气溶胶测量”（ACORES）野外活动的框架内，首次比较了这三种方法得出的 MBL 气溶胶通量。 气象使用直升机载测量平台ACTOS（机载云湍流观测系统）测量海洋对流层中的参数和气溶胶和云特性。这三种方法都用于估计MBL和FT之间的净粒子交换。在许多情况下，MLG 方法的夹带通量与 EC 和K在不确定范围内一致- 理论通量估计接近 MBL 的顶部，而不同方法的表面通量估计存在分歧。直升机载有效载荷无法直接在地表上方进行测量，这可能是地表通量不确定性的一个来源。在MBL顶部观测到的粒子通量在向上和向下方向都在0到10×10 ⁶  m ^-2  s ^-1之间，相关的不确定性在同一数量级上。尽管所有三种方法的不确定性都很大，但这项研究的结果有助于更好地理解 MBL 和 FT 之间的粒子传输及其在 MBL 中的分布。