Department of Physics, H N B University, Garhwal (A Central University), 246174 Srinagar, Uttarakhand, India.
Wadia Institute of Himalaya Geology, 33 GMS Road, Dehradun, 248001 Uttarakhand, India.
Environ Monit Assess. 2021 May 4;193(6):324. doi: 10.1007/s10661-021-09048-4.
Aerosol optical depth (AOD) and Ångström exponent (AE) are observed to be important parameters in understanding the status of ambient aerosol concentration over a particular location and depend not only upon the local but also on the large-scale dynamics of the atmosphere. The present article analyses the AOD and AE parameters retrieved with Moderate Resolution Imaging Spectrometer (MODIS) and Multi-angle Imaging Spectro-Radiometer (MISR) instruments onboard satellites, for the upper (Chamoli) and foothill (Dehradun) regions of Garhwal Himalaya in Uttarakhand, India, from 2006 to 2015. Aerosol properties are investigated at monthly, seasonal, and annual scales. The monthly mean values of MODIS-derived AOD and AE were observed to be 0.18 (± 0.14) and 1.05 (± 0.43) respectively over the Dehradun region. The seasonal maximums in AOD with MODIS and MISR were observed as 0.23 ± 0.06 and 0.29 ± 0.07 respectively in the pre-monsoon season, and the minimum values (0.099 ± 0.02) were observed in the post-monsoon season, over the Dehradun region. In contrast, in the Chamoli region, the maximum AOD (MODIS) was 0.21 ± 0.06 observed in the monsoon season and the minimum was 0.036 ± 0.007 in the post-monsoon season. Over a decade, the AE for Chamoli and Dehradun was found to vary from 0.07 to 0.17 and from 0.14 to 0.20 respectively. The median AE for Chamoli and Dehradun was found to be 1.49 and 1.47 respectively, marking the dominance of fine mode particles of anthropogenic origin. Observations show the presence of dust and polluted dust resulting from the long-range transport from the west. The comparison of AOD values from the two sensors shows a significant correlation (0.73) with slightly higher values from MISR over the year. The results obtained are important in understanding the climatic implications due to the atmospheric aerosols over the abovementioned Himalayan region of Uttarakhand, India.
气溶胶光学厚度（AOD）和 Ångström 指数（AE）被观察到是理解特定地点环境气溶胶浓度状况的重要参数，它们不仅取决于当地，还取决于大气的大尺度动力学。本文分析了从 2006 年到 2015 年，印度北阿坎德邦上加瓦尔喜马拉雅山脉的上部（钱莫利）和山前（德拉敦）地区，从中分辨率成像光谱仪（MODIS）和多角度成像光谱辐射计（MISR）卫星上获取的 AOD 和 AE 参数。气溶胶特性在月、季和年尺度上进行了研究。MODIS 衍生的 AOD 和 AE 的月平均值在德拉敦地区分别为 0.18（±0.14）和 1.05（±0.43）。MODIS 和 MISR 观测到的前季风季节 AOD 的季节性最大值分别为 0.23±0.06 和 0.29±0.07，德拉敦地区后季风季节的最小值为 0.099±0.02。相比之下，在钱莫利地区，季风季节的最大 AOD（MODIS）为 0.21±0.06，后季风季节的最小 AOD 为 0.036±0.007。在十年期间，钱莫利和德拉敦的 AE 从 0.07 到 0.17 和从 0.14 到 0.20 不等。钱莫利和德拉敦的 AE 中位数分别为 1.49 和 1.47，表明细颗粒物质主要来源于人为源。观测结果表明存在来自西部长距离传输的尘埃和污染尘埃。两个传感器的 AOD 值的比较显示出与 MISR 年值具有显著相关性（0.73），但 MISR 值略高。这些结果对于理解印度北阿坎德邦上述喜马拉雅地区大气气溶胶对气候的影响非常重要。
