25 March 2015

Long-term Trend and Sources of Carbonaceous Particles Measured in a Southeastern Tibetan Glacier

Summary

Black carbon (BC) and organic carbon (OC) particles—from forest fires, diesel engines, and other fuel combustion—ride on atmospheric currents and reach high and remote places such as the Tibetan Plateau, affecting snow melt and glaciers, which in turn record the history of these particles. Researchers at the Department of Energy’s Pacific Northwest National Laboratory and the Institute of Tibetan Plateau Research (Chinese Academy of Sciences) designed a new way to identify sources of these particles and the cause of their historical trend in a Tibetan glacier using a tracer tagging technique in a climate model (CAM5). They analyzed high temporal resolution measurements of BC and OC covering the time period of 1956–2006 in an ice core over the southeastern Tibetan Plateau that show a distinct seasonal dependence of BC and OC with higher respective concentrations but a lower OC/BC ratio in the non-monsoon season than during the summer monsoon. Using a global aerosol-climate model, in which BC emitted from different source regions can be explicitly tracked, they quantified BC source–receptor relationships between four Asian source regions and the southeastern Tibetan Plateau as a receptor.

The model results showed that BC recorded in the Southeastern Tibetan glacier originated in South Asia primarily during the non-monsoon season and all year round, followed by East Asia. The ice core record also indicates stable and relatively low BC and OC deposition fluxes from the late 1950s to 1980, but an overall increase to recent years, a trend consistent with the BC and OC emission inventories and the fuel consumption of South Asia. Moreover, the increasing trend of the OC/BC ratio since the early 1990s indicates a growing contribution of coal combustion and/or biomass burning to the emissions. The estimated radiative forcing induced by BC and OC impurities in snow has increased since 1980, suggesting an increasing potential influence of carbonaceous aerosols on the Tibetan glacier melting and the availability of water resources in the surrounding regions. The findings contribute to insights into the impact of carbonaceous particles on glacier melting and potential mitigation actions.  

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Acknowledgments

This work was supported by the China National Funds for Distinguished Young Scientists and the National Natural Science Foundation of China, including 41125003, 41101063, and 2009CB723901. H. Wang, Y. Qian and P. J. Rasch were supported by the US Department of Energy (DOE), Office of Science, Biological and Environmental Research as part of the Earth System Modeling program. R. Zhang acknowledges support from the China Scholarship Fund. PNNL is operated for DOE by Battelle Memorial Institute under contract DE-AC05-76RLO1830. The National Center for Atmospheric Research is sponsored by the National Science Foundation. We thank Z. Guo and S. Yang for providing the observations of snow.