The present study investigates the influencing factors responsible for the asymmetry in aerosol optical depth (AOD) trends using long-term datasets (2003–2019) over western and eastern Indo-Gangetic Plain (IGP) regions during the pre-monsoon season. Analysis from Modern-Era Retrospective Analysis for Research and Applications Version-2 (MERRA-2) for different aerosols illustrates that dust aerosols dominate over the western IGP (W-IGP), while sulphate and carbonaceous aerosols (black carbon (BC) and organic carbon (OC)) majorly contributed to the total AOD over the eastern IGP (E-IGP). Our study reveals a significant decline in AOD over the W-IGP, while a rising trend over E-IGP from Moderate Resolution Imaging Spectroradiometer (MODIS) satellite observations. A dipole pattern in AOD trends over IGP indicates the aerosol loading from combined effects of various natural and anthropogenic emissions under favourable meteorological conditions over the W-IGP and E-IGP, respectively. Furthermore, the declining AOD trend over W-IGP is mainly attributed to increased pre-monsoonal rainfall, which supports the wet deposition, increases soil moisture, thus reducing soil erodibility, and correlates strongly with meteorological factors. The rising AOD trend over the E-IGP appears to be influenced by increased anthropogenic emissions (i.e., BC, OC, and sulphate) from the industrialization of the region, decreased rainfall, and enhanced westerly-induced advection of aerosols from W-IGP. Our study indicates that the regional meteorological variables and anthropogenic sources influence changes in the AOD trends over the IGP region.

中文翻译：

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利用遥感观测探索印度恒河平原气溶胶不对称趋势的影响因素

本研究利用季风前季节印度恒河平原（IGP）西部和东部地区的长期数据集（2003-2019）调查了造成气溶胶光学深度（AOD）趋势不对称的影响因素。现代时代研究和应用回顾分析第 2 版 (MERRA-2) 对不同气溶胶的分析表明，灰尘气溶胶在西部 IGP (W-IGP) 中占主导地位，而硫酸盐和碳质气溶胶（黑碳 (BC) 和有机物）碳（OC））对东部 IGP（E-IGP）的总 AOD 贡献很大。我们的研究表明，根据中分辨率成像光谱仪 (MODIS) 卫星观测，W-IGP 的 AOD 显着下降，而 E-IGP 的 AOD 呈上升趋势。 IGP 上 AOD 趋势的偶极模式分别表明了 W-IGP 和 E-IGP 上有利气象条件下各种自然和人为排放的综合影响所产生的气溶胶负荷。此外，W-IGP的AOD下降趋势主要归因于季风前降雨的增加，这支持了湿沉降，增加了土壤湿度，从而降低了土壤的可蚀性，并且与气象因素密切相关。 E-IGP 上 AOD 的上升趋势似乎受到该地区工业化导致的人为排放（即 BC、OC 和硫酸盐）增加、降雨量减少以及 W-IGP 西风引起的气溶胶平流增强的影响。我们的研究表明，区域气象变量和人为源影响 IGP 地区 AOD 趋势的变化。