青藏高原雪冰中碳质气溶胶含量变化

Carbonaceous aerosols in snow and ice in the Tibetan plateau

文中采用供氧两步加热的方法对过滤到石英膜上的雪冰中碳质气溶胶含量进行分析,其中有机碳(OC)和元素碳(EC)分别在340和650℃的条件下进行热解、氧化分离,生成的CO2转化成CH4并由气相色谱仪氢火焰离子化检测器(FID)检测其含量。空白测试表明,该系统的OC本底值为(0·50±0·04)(1σ)μgC,EC为(0·38±0·04)(1σ)μgC。利用这套分析系统对青藏高原8条冰川的34个雪冰和降水样品中OC和EC的含量进行了测试。结果表明,在青藏高原雪冰中OC和EC含量自东向西、自北向南呈明显的下降趋势(西昆仑除外)。在高原东北部EC的质量分数相对较高,平均为79·2ng·g-1;在喜马拉雅西段EC的质量分数最低,平均为4·3ng·g-1。在冰川表面,雪的融化使雪冰中碳质气溶胶聚集,并导致其含量明显升高,该过程降低了雪表面的反照率,加速了冰川的消融。

An optimization of a 2-step thermal method was used to determine organic carbon （OC） and element carbon （EC） concentrations in snow and ice from the Tibetan plateau. OC is removed from the quartz filter under a pure oxygen atmosphere during the first combustion step at 340 ℃. The remaining carbon defined as EC is oxidized at the next combustion temperature of 650 ℃. Background contamination of 0. 50±0. 04 （1σ）μg C for OC, and 0.38±0. 04 （1σ）μg C for EC are determined by blank tests. EC and OC concentrations in snow samples collected from 8 glaciers in the Tibetan plateau were analyzed by this method. The results allow quantification for the first time of the different carbonaceous particle contents in the Tibetan plateau and other regions. The concentrations of EC and OC particles in snow in the Plateau show a clear decreasing trend, excluding the west Kunlun region, from east to west and from north to south. The highest mean EC content, 79.2 ng · g^-1, was found in the northeast region, and the lowest, 4.3 ng · g^-1, in the western Himalayas. We note that snow melting will result in accumulation of carbonaceous particles on glaciers, which suggests that such melting can reduce snow albedo and accelerate glacier shrinking.