利用双碳同位素解析青藏高原大气和雪冰中吸光碳质气溶胶来源的研究

Qinghai-Tibet Plateau (QTP) is one of the most sensitive regions to the climate change in the world. Light-absorbing carbonaceous aerosols, i.e., black carbon (BC) and brown carbon (BrC), are not only the important pollutants that leading to the degradation of atmospheric visibility and the occurrence of air pollution or haze, but also can absorb solar radiation, influence hydro-thermal circulation, and play a critical role in the climate change and the shrinking of glaciers in QTP. However, a large uncertainty exist with respect to the emission sources of BC and BrC, which significantly constraint the understanding of the predicted changes of climate and the glaciers in this key area. Recently, dual-carbon isotope-based (radiocarbon,14C and stable carbon isotope, 13C) technique has been successfully employed in the source apportionment of carbonaceous aerosols in the atmosphere. In this project, we will firstly use 14C and 13C together to quantify the contributions of coal, petroleum, C3 plant, and C4 plant to BC and BrC in the atmosphere and snow in QTP, and to demonstrate their temporal and spatial variations and the corresponding influencing factors by coupling the measurements of other tracers such as levoglucosan and water-soluble inorganic ions and Hybrid Single Particle Lagrangian Integrated Trajectory Model (HYSPLIT). In addition, we will find out the most important sources that controlling the mass absorption efficiency (MAE) of BC and BrC. From these results we will get a better understanding of knowledge for the emission sources of BC and BrC, and reduce the uncertainty of the climate change models as well.

青藏高原是地球上受气候变化影响最为敏感的地区之一。吸光碳质气溶胶（黑碳和棕碳），不仅是重要的污染物，导致大气能见度降低，诱发大气污染和灰霾，而且能吸收太阳辐射，影响水热循环，对青藏高原气候变化和冰川加速融化起重要作用。然而，黑碳和棕碳的排放源仍然具有巨大的不确定性，严重限制了科学家对这一重要地区气候和冰川变化的认识。近年来，联合使用双碳同位素，即放射性碳（14C）和稳定碳同位素（13C），在碳质气溶胶上表现出了强大的源解析能力。本项目将首次利用14C和13C定量解析重要污染源（煤、石油、C3植物和C4植物）对青藏高原大气和雪冰中黑碳和棕碳的贡献，结合气团后向轨迹模型和其它示踪化合物（左旋葡聚糖和水溶性无机离子），着力阐述不同排放源的时空变化规律和影响因素。此外，查明对黑碳和棕碳吸光能力影响最为重要的污染源。研究结果对厘清青藏高原吸光碳质气溶胶来源和降低气候预测不确定性具有重要的意义。

吸光碳质气溶胶（黑碳和棕碳）在空气质量恶化和气候变化上扮演着重要的角色，其来源具有非常显著的区域特征和不确定性。本项目以青藏高原（第三极）为目标研究区域，对其大气气溶胶和表层降雪的化学组成、来源和吸光能力以及影响因素进行了探讨，重点取得了以下结果：（1）青藏高原典型城市拉萨的大气气溶胶组分具有显著的季节变化特征，明显受南亚和西亚地区排放源的影响；（2）放射性碳分析结果显示，化石燃料对拉萨夏季黑碳气溶胶的贡献约为90%，生物质燃烧贡献约为10%；在冬春季节，生物质燃烧对黑碳气溶胶的贡献可以达到40%以上，可能与冬春季节的取暖活动有关系；（3）稳定碳同位素分析结果表明拉萨部分黑碳气溶胶可能与天然气燃烧存在关系，需引起政府部门的重视；（4）青藏高原表层雪溶解性有机碳（DOC）的浓度范围在0.16 – 6.81 mg L-1之间，平均值为2.49 mg L-1。放射性碳分析结果表明DOC主要来自生物源，表明棕碳主要来自于生物质燃烧。本项目双碳同位素为主要技术手段，较为系统地量化了化石燃料对青藏高原地区气溶胶的影响，对后续准确评估青藏高原空气质量和气候变化具有重要的参考价值。