A novel back-trajectory analysis of the origin of black carbon transported to the Himalayas and Tibetan Plateau during 1996−2010

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Description

Black carbon (BC) deposited on snow and ice can reduce the surface albedo and consequently accelerate glacier melting. Surrounded by the world’s two largest BC-generating regions (South Asia and East Asia), the Himalayas and Tibetan Plateau (HTP, also known as Earth’s “third pole”) is encountering a rapid climate change and glacier retreat since 1990s, for which BC transported to the HTP was reported to be the major reason. In support of the Ganges Valley Aerosol Experiment (GVAX), a novel back-trajectory approach that takes into account all the atmospheric processes related to BC (e.g., emissions, hydrophilic-to-hydrophobic conversion, and dry/wet deposition) is developed on the basis of the framework of the Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model to evaluate the BC origin reaching the HTP during 1996−2010. The results indicate that BC received by the HTP increased by 41% from 1996 to 2010 with a linear annual growth rate of 2.5%, implying that the BC problem is accelerating in the HTP region. BC sources that influence the HTP vary with seasons. On an annual basis, South Asia and East Asia are the main source regions, accounting for 67% and 17% of BC transported to the HTP, followed by Former USSR (~8%), Middle East (~4%), Europe (~2%), and Northern Africa (~1%). Although annual BC emission in China is at least 80% higher than that in India, its contribution to BC on the HTP is smaller. Examining the sectoral distributions, the contributions of residential, industry, land transportation, and agricultural waste burning to the EEI are 60±5%, 17±3%, 15±5%, and 6±3%, respectively. Open forest burning has significant interannual and seasonal variability, accounting for 11% of the BC transported to the HTP in 1999 when extensive forest burning occurred. Showing significant monthly variations, BC reaching the HTP is high in winter and low in summer, which is attributed to the effective wet scavenging of BC during the summer monsoon season. We show the seasonal spatial distribution of BC sources directly on a 0.5º x 0.5º grid, and it directly identifies the hotspots of sources (e.g., the Indo-Gangetic Plain of India and the Sichuan Basin of China) and provides information to policymakers about the best target areas for mitigating the climate changes and other effects on the HTP.