Abstract A better understanding of aerosol optical, microphysical and radiative properties is a crucial challenge for climate change studies. In the present study, column-integrated aerosol optical and radiative properties observed at a rural site, Mbita (0.42°S, 34.20 °E, and 1125 m above sea level) located in Kenya, East Africa (EA) are investigated using ground-based Aerosol Robotic Network (AERONET) data retrieved during January, 2007 to December, 2015. The annual mean aerosol optical depth (AOD500 nm), Angstrom exponent (AE440–870 nm), fine mode fraction of AOD500 nm (FMF500 nm), and columnar water vapor (CWV, cm) were found to be 0.23 ± 0.08, 1.01 ± 0.16, 0.60 ± 0.07, and 2.72 ± 0.20, respectively. The aerosol optical properties exhibited a unimodal distribution with substantial seasonal heterogeneity in their peak values being low (high) during the local wet (dry) seasons. The observed data showed that Mbita and its environs are significantly influenced by various types of aerosols, with biomass burning and/or urban-industrial (BUI), mixed (MXD), and desert dust (DDT) aerosol types contributing to 37.72%, 32.81%, and 1.40%, respectively during the local dry season (JJA). The aerosol volume size distribution (VSD) exhibited bimodal lognormal structure with a geometric mean radius of 0.15 μm and 3.86–5.06 μm for fine- and coarse-mode aerosols, respectively. Further, analysis of single scattering albedo (SSA), asymmetry parameter (ASY) and refractive index (RI) revealed dominance of fine-mode absorbing aerosols during JJA. The averaged aerosol direct radiative forcing (ARF) retrieved from the AERONET showed a strong cooling effect at the bottom of the atmosphere (BOA) and significant warming within the atmosphere (ATM), representing the important role of aerosols played in this rural site of Kenya. Finally, the Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) model revealed that aerosols from distinct sources resulted in enhanced loading during JJA.

中文翻译：

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东非肯尼亚热带农村地区气溶胶的光学、微物理和辐射特性：来源识别、修改和气溶胶类型判别

摘要 更好地了解气溶胶的光学、微物理和辐射特性是气候变化研究的关键挑战。在本研究中，在位于东非肯尼亚 (EA) 的农村地点 Mbita（0.42°S、34.20°E 和 1125 m 海拔）观察到的柱集成气溶胶光学和辐射特性使用地面-基于 2007 年 1 月至 2015 年 12 月检索的气溶胶机器人网络 (AERONET) 数据。年平均气溶胶光学深度 (AOD500 nm)、埃指数 (AE440–870 nm)、AOD500 nm 的精细模式分数 (FMF500 nm)，柱状水蒸气 (CWV, cm) 分别为 0.23 ± 0.08、1.01 ± 0.16、0.60 ± 0.07 和 2.72 ± 0.20。气溶胶光学特性表现出单峰分布，在局部湿（干）季其峰值低（高）具有显着的季节性异质性。观测数据表明，Mbita 及其周边地区受各种气溶胶类型的影响显着，其中生物质燃烧和/或城市工业 (BUI)、混合 (MXD) 和沙漠粉尘 (DDT) 气溶胶类型贡献了 37.72%、32.81 % 和 1.40%，分别在当地旱季 (JJA)。气溶胶体积粒径分布 (VSD) 表现出双峰对数正态结构，细模和粗模气溶胶的几何平均半径分别为 0.15 μm 和 3.86-5.06 μm。此外，对单次散射反照率 (SSA)、不对称参数 (ASY) 和折射率 (RI) 的分析揭示了 JJA 期间细模式吸收气溶胶的主导地位。从 AERONET 获取的平均气溶胶直接辐射强迫 (ARF) 显示出大气底部 (BOA) 的强烈冷却效应和大气内显着变暖 (ATM)，代表气溶胶在肯尼亚农村地区发挥的重要作用. 最后，混合单粒子拉格朗日综合轨迹 (HYSPLIT) 模型显示，来自不同来源的气溶胶在 JJA 期间导致负载增加。