Identifying spatio-temporal climatic characteristics and events of the South-Asian aerosol pollution transport to the Tibetan Plateau

Abstract

South Asian aerosol pollutants can be transported to the Tibetan Plateau (TP) and affect the local atmospheric environment; however, few studies have produced statistical results for the long term. In this study, 41 years of pollution transport events from South Asia to the TP were screened based on Modern-Era Retrospective Analysis for Research and Applications, Version 2 (MERRA-2) reanalysis data using objective methods, and the main pollution transport mechanisms were revealed. We used the empirical orthogonal functions (EOF) and the rotated empirical orthogonal functions (REOF) methods to obtain the spatiotemporal variation characteristics of the aerosol optical depth (AOD) over the TP and the large loading regions of AOD variation from 1980 to 2020 and combined them with the backward trajectory to screen for severe pollution events in the TP influenced by transport from South Asia. The three regions (eastern, central and western regions) with large AOD loading variations in the southern TP are shown by the REOF. Based on the objectively defined AOD indices for the three regions, 2058 days of strong pollution were identified, of which 1702 days (82.7%) were affected by pollution transport from South Asia. Of these 1702 days, the central region had the highest number of days at 661 (38.8%), followed by the western and eastern regions with 544 (32%) and 497 (29.2%) days, respectively. The results obtained from the transport events in the three regions suggest that South Asian pollutants can be transported across the Himalayas to the TP by valley winds, north-south valley passages, and cyclonic uplift. These findings deepen the understanding of the aerosol pollution of the TP affected by pollution transport from South Asia.