Understanding aerosol vertical distribution is crucial for aerosol pollution mitigation but is hindered by limited observational data. This study employed multiaxis differential optical absorption spectroscopy (MAX-DOAS) technology with a coupled radiative transfer model-machine learning (RTM-ML) framework to retrieve high-resolution aerosol optical properties in Shanghai. Retrievals indicated vertically decreasing aerosols, peaking in the upper atmosphere in the summer and in the lower atmosphere in the winter. Aerosol hygroscopicity followed similar seasonal patterns but increased with the altitude. Multifactor driving ML models and Shapley additive explanations (SHAP) were used to investigate the drivers to aerosol variation. Results indicated that emissions, east–west transport, and atmospheric oxidation were the main drivers of aerosols below 0.5 km. Above 0.5 km, humidity and atmospheric oxidation became dominant, suggesting that hygroscopic growth and secondary aerosol formation were more prominent. North–south transport also significantly influenced aerosol distribution within 0.5 to 1.6 km. Meteorological normalization emphasized that emission reduction can effectively lower aerosols in the lower atmosphere, while enhanced atmospheric oxidation promoted secondary aerosol formation, particularly in the upper atmosphere. These findings advance the understanding of multiple factors in shaping the vertical aerosol distributions and highlight that emission reduction strategies for addressing compound pollution should be conceived with a multidimensional and multifactorial understanding.

中文翻译：

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探索气溶胶垂直分布及其影响因素：来自 MAX-DOAS 和机器学习的见解

了解气溶胶垂直分布对于减轻气溶胶污染至关重要，但受到有限观测数据的阻碍。本研究采用多轴差分光吸收光谱 （MAX-DOAS） 技术和耦合辐射传输模型-机器学习 （RTM-ML） 框架来检索上海地区的高分辨率气溶胶光学特性。检索结果表明气溶胶垂直减少，夏季在高层大气中达到峰值，冬季在低层大气中达到峰值。气溶胶吸湿性遵循相似的季节性模式，但随着海拔的增加而增加。多因素驾驶 ML 模型和 Shapley 加法解释 （SHAP） 用于研究气溶胶变化的驱动因素。结果表明，排放、东西向传输和大气氧化是 0.5 km 以下气溶胶的主要驱动因素，在 0.5 km 以上，湿度和大气氧化成为主导因素，表明吸湿性生长和二次气溶胶形成更为突出。南北向运输也显著影响了 0.5 至 1.6 公里内的气溶胶分布。气象正常化强调减排可以有效降低低层大气中的气溶胶，而增强的大气氧化促进了二次气溶胶的形成，尤其是在高层大气中。这些发现促进了对塑造垂直气溶胶分布的多个因素的理解，并强调解决化合物污染的减排战略应该在多维和多因素的理解下进行构想。