Articles | Volume 17, issue 19
Research article
09 Oct 2017
Research article |  | 09 Oct 2017

Re-evaluating black carbon in the Himalayas and the Tibetan Plateau: concentrations and deposition

Chaoliu Li, Fangping Yan, Shichang Kang, Pengfei Chen, Xiaowen Han, Zhaofu Hu, Guoshuai Zhang, Ye Hong, Shaopeng Gao, Bin Qu, Zhejing Zhu, Jiwei Li, Bing Chen, and Mika Sillanpää

Abstract. Black carbon (BC) is the second most important warming component in the atmosphere after CO2. The BC in the Himalayas and the Tibetan Plateau (HTP) has influenced the Indian monsoon and accelerated the retreat of glaciers, resulting in serious consequences for billions of Asian residents. Although a number of related studies have been conducted in this region, the BC concentrations and deposition rates remain poorly constrained. Because of the presence of arid environments and the potential influence of carbonates in mineral dust (MD), the reported BC concentrations in the HTP are overestimated. In addition, large discrepancies have been reported among the BC deposition derived from lake cores, ice cores, snow pits and models. Therefore, the actual BC concentration and deposition values in this sensitive region must be determined. A comparison between the BC concentrations in acid (HCl)-treated and untreated total suspected particle samples from the HTP showed that the BC concentrations previously reported for the Nam Co station (central part of the HTP) and the Everest station (northern slope of the central Himalayas) were overestimated by approximately 52 ± 35 and 39 ± 24 %, respectively, because of the influence of carbonates in MD. Additionally, the organic carbon (OC) levels were overestimated by approximately 22 ± 10 and 22 ± 12 % for the same reason. Based on previously reported values from the study region, we propose that the actual BC concentrations at the Nam Co and Everest stations are 61 and 154 ng m−3, respectively. Furthermore, a comprehensive comparison of the BC deposition rates obtained via different methods indicated that the deposition of BC in HTP lake cores was mainly related to river sediment transport from the lake basin as a result of climate change (e.g., increases in temperature and precipitation) and that relatively little BC deposition occurred via atmospheric deposition. Therefore, previously reported BC deposition rates from lake cores overestimated the atmospheric deposition of BC in the HTP. Correspondingly, BC deposition derived from snow pits and ice cores agreed well with that derived from models, implying that the BC depositions of these two methods reflect the actual values in the HTP. Therefore, based on reported values from snow pits and ice cores, we propose that the BC deposition in the HTP is 17. 9 ± 5. 3 mg m−2 a−1, with higher and lower values appearing along the fringes and central areas of the HTP, respectively. These adjusted BC concentrations and deposition values in the HTP are critical for performing accurate evaluations of other BC factors, such as atmospheric distribution, radiative forcing and chemical transport in the HTP.

Short summary
In this study, we found, due to contribution of carbonates, previously reported BC concentration in atmosphere of the Himalayas and Tibetan Plateau (HTP) were overestimated by around 39–52 %. Meanwhile, we found BC deposition of lake cores overestimated the atmospheric deposition of BC in the HTP; BC depositions of glacier region reflected actual values of 17.9 ± 5.3 mg m−2 a−1. The above results are critical for studying atmospheric distribution and chemical transport of BC in and around the HTP.
Final-revised paper