National Remote Sensing Centre, Indian Space Research Organisation, Hyderabad, India.
, F1 North Park Apts, Thrissur, India.
Environ Sci Pollut Res Int. 2018 Jun;25(18):18147-18160. doi: 10.1007/s11356-018-2032-0. Epub 2018 Apr 25.
The study examines trends of scattering, absorption and total aerosol optical depths (SAOD, AAOD and AOD) over India and surrounding oceanic regions and explores role of local production, long-range transport and atmospheric dynamics on observed trends. Long-term satellite observations are used to estimate trends and assess their statistical significance. Significant spatial and seasonal changes are observed in trends of SAOD, AAOD and AOD. AOD is observed to be increasing during post monsoon and winter over most of the land mass and surrounding oceanic regions, whereas decreasing trends over land and increasing trends over oceanic regions are observed in pre-monsoon and summer months. In general, SAOD and AAOD show similar trends (if there is any) as that of AOD over most of the regions in most of the months. Strongest positive trends over land regions are observed in November with trend of AOD greater than 0.01 year, especially over Indo-Gangetic Plain (IGP). Increase of AOD over IGP in post monsoon is contributed significantly by absorbing aerosols with rate of increase ~ 0.005 AAOD year. AAODs are observed to be increasing over Arabian Sea and Bay of Bengal (BoB) in December also, with rate ~ 0.003 AAOD year. Strongest positive trends over Arabian Sea and BoB are observed in June with rate of increase greater than 0.02 AOD year, whereas strong negative trends are observed over north-west India in the same period with rate of decrease greater than 0.02 AOD year. Over IGP, AOD, AAOD and SAOD show contrasting trends in winter and summer seasons. AAOD exhibits strongest decreasing trend over IGP during April-June. Positive trends of AOD over Arabian Sea and BoB are favoured significantly by changes in circulation dynamics. Atmospheric convergence is observed to be strengthening over these regions in April and June, leading to more accumulation and hence positive trends of AOD. Aerosol transport over to the Arabian Sea is observed to be enhancing and contributing significantly to AOD increase over the Arabian Sea in pre-monsoon and summer months. Enhancement in aerosol transport over to the Arabian Sea is observed in pre-monsoon at higher altitudes above 3 km, whereas it is observed in summer at lower levels. However, decreasing trends of AOD over north-west India and IGP during pre-monsoon and summer are observed to be due to decrease in aerosol transport from the continental regions at the west.
本研究考察了印度及周边海域的散射、吸收和总气溶胶光学深度（SAOD、AAOD 和 AOD）的变化趋势，并探讨了本地生成、长距离传输和大气动力对观测到的趋势的作用。长期卫星观测用于估计趋势并评估其统计显著性。SAOD、AAOD 和 AOD 的趋势存在显著的时空变化。在大多数陆地和周边海域，后季风和冬季期间 AOD 呈增加趋势，而在季风前和夏季，陆地呈下降趋势，海洋呈上升趋势。一般来说，SAOD 和 AAOD 在大多数月份的大多数地区与 AOD 的趋势相似（如果有的话）。陆地地区最强的正趋势出现在 11 月，AOD 的趋势大于 0.01 年，特别是在印度恒河平原（IGP）。IGP 后季风期间 AOD 的增加主要是由吸收性气溶胶引起的，增长率约为 0.005 AAOD 年。12 月也观察到阿拉伯海和孟加拉湾（BoB）的 AAOD 增加，增长率约为 0.003 AAOD 年。阿拉伯海和 BoB 最强的正趋势出现在 6 月，增长率大于 0.02 AOD 年，而同期印度西北部则出现强烈的负趋势，增长率大于 0.02 AOD 年。在 IGP，AOD、AAOD 和 SAOD 在冬季和夏季表现出相反的趋势。在 4 月至 6 月期间，IGP 上的 AAOD 表现出最强的下降趋势。阿拉伯海和 BoB 上 AOD 的正趋势主要受环流动力学变化的影响。在 4 月和 6 月，观测到这些地区的大气辐合增强，导致更多的积累，从而导致 AOD 的正趋势。观测到气溶胶向阿拉伯海的输送增强，并在季风前和夏季对阿拉伯海上的 AOD 增加有显著贡献。在季风前，气溶胶向阿拉伯海的输送增强发生在 3 公里以上的较高海拔，而在夏季则发生在较低海拔。然而，在季风前和夏季，印度西北部和 IGP 的 AOD 下降趋势是由于来自西部大陆地区的气溶胶输送减少所致。
