Black Carbon Size in Snow of Chinese Altai Mountain in Central Asia

Abstract

Black carbon (BC) in snow plays an important role to accelerate snow melting. However, current studies mostly focused on BC concentrations, few on their size distributions in snow which affected BC’s effect on albedo changes. Here we presented refractory BC (rBC) concentrations and size distributions in snow collected from Chinese Altai Mountains in Central Asia from November 2016 to April 2017. The results revealed that the average rBC concentrations were 5.77 and 2.82 ng g⁻¹ for the surface snow and sub-surface snow, which were relatively higher in the melting season (April) than that in winter (November–January). The mass median volume-equivalent diameter of rBC size in surface snow was approximately at 120–150 nm, which was typically smaller than that in the atmosphere (about 200 nm for urban atmosphere). However, there existed no specific mass median volume-equivalent diameter of BC size for sub-surface snow in winter. While during the melting season, the median mass size of rBC in sub-surface snow was similar to that in surface snow. Backward trajectories indicated that anthropogenic sourced BC dominated rBC in snow (70%–85%). This study will promote our understanding on BC size distributions in snow, and highlight the possible impact of BC size on climate effect.

摘 要

雪冰中的黑碳对加速积雪消融具有重要作用。然而,目前的研究大多集中于黑碳浓度的影响,很少关注积雪中黑碳粒径的分布,这显著影响黑碳对反照率变化的评估。鉴于此,我们于2016年11月至2017年4月在北疆阿勒泰地区开展了积雪中难熔黑碳浓度和粒径分布的研究。结果表明,表雪和次表层雪的黑碳平均浓度分别为5.77和2.82 ng g−1,且在融雪季节(4月)相对冬季(11月至1月)偏高。表雪中黑碳粒径的质量中值直径约为120−150 nm,小于大气中黑碳颗粒的直径(城市大气中约为200 nm)。然而,冬季次表层雪中黑碳粒径的质量中值直径不明显,而在融雪季节,次表层雪中黑碳的中值粒径与表层雪中相似。结合火点资料的后向轨迹表明,北疆阿勒泰地区积雪中人为源黑碳占主导(70%−85%)。该研究将进一步促进我们对雪中黑碳粒径分布的理解,并为评估黑碳粒径大小对气候效应的可能影响提供基础数据。

Electronic Supplementary Material to

Black Carbon Size in Snow of Chinese Altai Mountain in Central Asia