Abstract. The southeast Atlantic region, characterized by persistent stratocumulus clouds, has one of the highest uncertainties in aerosol radiative forcing and significant variability across climate models. In this study, we analyze the seasonally varying role of marine aerosol sources and identify key uncertainties in aerosol composition at cloud-relevant altitudes over the southeast Atlantic using the GEOS-Chem chemical transport model. We evaluate simulated aerosol optical depth (AOD) and speciated aerosol concentrations against those collected from ground observations and aircraft campaigns such as LASIC, ORACLES, and CLARIFY, conducted during 2017. The model consistently underestimates AOD relative to AERONET, particularly at remote locations like Ascension Island. However, when compared with aerosol mass concentrations from aircraft campaigns during the biomass burning period, it performs adequately at cloud-relevant altitudes, with a normalized mean bias (NMB) between −3.5 % (CLARIFY) and −7.5 % (ORACLES). At these altitudes, organic aerosols (63 %) dominate during the biomass burning period, while sulfate (41 %) prevails during austral summer, when dimethylsulfide (DMS) emissions peak in the model. Our findings indicate that marine sulfate can account for up to 69 % of total sulfate during high DMS period. Sensitivity analyses indicate that refining DMS emissions and oxidation chemistry may increase sulfate aerosol produced from marine sources, highlighting their overall importance. Additionally, we find marine primary organic aerosol emissions may substantially increase total organic aerosol concentrations, particularly during austral summer. This study underscores the imperative need to refine marine emissions and their chemical transformations to better predict aerosol-cloud interactions and reduce uncertainties in aerosol radiative forcing over the southeast Atlantic.

中文翻译：

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使用化学传输模型量化东南大西洋海洋气溶胶的影响：气溶胶-云相互作用的影响


摘要。东南大西洋地区以持续性层积云为特征，是气溶胶辐射强迫不确定性最高的地区之一，气候模型的变异性也很大。在这项研究中，我们分析了海洋气溶胶来源随季节变化的作用，并使用 GEOS-Chem 化学输运模型确定了东南大西洋云相关高度的气溶胶成分的关键不确定性。我们根据 2017 年期间进行的地面观测和 LASIC、ORACLES 和 CLARIFY 等飞机活动收集的数据来评估模拟气溶胶光学深度 (AOD) 和特定气溶胶浓度。该模型相对于 AERONET 始终低估 AOD，特别是在阿森松岛等偏远地区岛。然而，与生物质燃烧期间飞机活动的气溶胶质量浓度相比，它在云相关高度上表现良好，归一化平均偏差 (NMB) 在 -3.5% (CLARIFY) 和 -7.5% (ORACLES) 之间。在这些海拔高度，有机气溶胶 (63%) 在生物质燃烧期间占主导地位，而硫酸盐 (41%) 在南半球夏季占主导地位，此时模型中二甲硫醚 (DMS) 排放达到峰值。我们的研究结果表明，在高 DMS 时期，海洋硫酸盐可占硫酸盐总量的 69%。敏感性分析表明，精炼 DMS 排放和氧化化学可能会增加海洋来源产生的硫酸盐气溶胶，凸显其总体重要性。此外，我们发现海洋初级有机气溶胶排放可能会大幅增加总有机气溶胶浓度，特别是在南方夏季。 这项研究强调了改进海洋排放及其化学转化的迫切需要，以更好地预测气溶胶-云相互作用并减少东南大西洋气溶胶辐射强迫的不确定性。