| 摘要: |
| 黑碳是一种吸光物质，对全球变暖和区域气候变化具有重要作用；青藏高原又在气候、水资源、生物多样性、碳收支平衡等方面具有重要的生态作用。为了解青藏高原东南缘地区黑碳的污染特征及其来源，于云南省丽江市高美古地区进行春季（2018-03-15—2018-05-13）样品采集，采用热/光碳分析仪测定元素碳（EC）浓度，探究污染特征（EC、char-EC、soot-EC）、光学特征（babs、MAE），并基于正定矩阵因子分解法（PMF）和后向轨迹分析其来源。结果表明：春季EC浓度受生物质燃烧、旅游旺季等人为排放和沙尘等自然因素共同影响；EC与温差和太阳辐射呈正相关，与湿度呈显著负相关。Char-EC和soot-EC平均质量浓度分别为(0.35±0.20) μg·m−3和(0.07±0.04) μg·m−3，两者在EC中的占比分别为80.1%和19.9%。Char-EC/soot-EC比值均大于1，表明该区域受到生物质和煤炭燃烧影响较大。babs和MAE值在4月22日前后差异较大，主要与不同时期污染源占比有关。青藏高原东南缘EC主要受缅甸东北部气团传输影响，主要污染类型有生物质燃烧、扬尘、煤炭燃烧和交通源，其中生物质燃烧和扬尘源贡献占主导地位。 |
| 关键词: 元素碳 青藏高原 正定矩阵因子分解法 后向轨迹 |
| DOI：10.7515/JEE222055 |
| CSTR：32259.14.JEE222055 |
| 分类号: |
| 基金项目:国家自然科学基金项目（42192512，41877391）；第二次青藏高原综合科学考察研究（2019QZKK0602）；中国科学院青年创新促进会（2019402） |
| 英文基金项目:National Natural Science Foundation of China (42192512, 41877391); The Second Tibetan Plateau Scientific
Expedition and Research Program (STEP) (2019QZKK0602); Youth Innovation Promotion Association of
the Chinese Academy of Sciences (2019402) |
|
| Characteristics and sources of EC pollution in the southeastern margin of the Tibetan Plateau |
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WANG Jin, WANG Qiyuan, LI Li, TIAN Jie, RAN Weikang, ZHANG Yong, CHEN Shuoyuan
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1. Key Laboratory of Aerosol Chemistry and Physics, Institute of Earth Environment, Chinese Academy of Sciences, Xi’an 710061, China
2. University of Chinese Academy of Sciences, Beijing 100049, China
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| Abstract: |
| Background, aim, and scope Black carbon (or elemental carbon, EC) is a light-absorbing substance that is a major driver of global warming and regional climate change, and the Tibetan Plateau is of ecological importance in terms of climate, water resources, and biodiversity; additionally, it has a role in maintaining the carbon budget balance. The black carbon concentration in this region is relatively low, but its impact extends beyond the Tibetan Plateau to influence the air quality and climate in Asia and even the wider northern hemisphere. Therefore, it is vital to explore the characteristics of black carbon pollution in the Tibetan Plateau region. In this study, we analyzed the pollution (EC, char-EC, and soot-EC) and optical characteristics (absorption coefficient: babs; mass absorption efficiency: MAE) of black carbon as well as the pollution sources in the southeastern margin of the Tibetan Plateau (Gaomeigu) in springtime. Materials and methods The sampling instrument was a TE-6070 (Tisch, USA) high-flow sampler with a flow rate of 1.13 m3·min−1, and the filter membrane was a quartz filter membrane (Whatman, USA). The sampling time was from Mar. 15, 2018, to May 13, 2018. Laboratory-determined carbon fractions (organic carbon (OC) and EC) and elemental fractions were analyzed using a DRI Model 2001 thermo-optical carbon analyzer and an energy dispersion-X-ray fluorescence analyzer, respectively. After calibration, the positive matrix factorization model and trajectory clustering were used for source analysis. Results The peak value of EC in Mar. (1.4 μg·m−3) was mainly attributable to fireworks emissions at a large festival (Naxi) in Lijiang, whereas the peak value of EC in Apr. (1.9 μg·m−3) was mainly attributable to dust. Due to spring being travel season, anthropogenic emissions were also a notable source at this time. EC was positively correlated with solar radiation and negatively correlated with humidity. Precipitation had a clear effect on EC. Compared with soot-EC, char-EC had a higher proportion of EC, but its fluctuation of concentration was smaller. The char-EC/soot-EC ratio was greater than 1 for all observations, indicating that this region is greatly influenced by biomass and coal combustion. The babs and MAE values were significantly different on the days around Apr. 22, which was attributable to the proportion of pollution sources in different periods. EC concentration in the southeastern margin of the Tibetan Plateau was mainly affected by air transport from northeastern Myanmar, and the main pollution sources were biomass combustion, coal combustion, dust, and traffic sources, among which biomass combustion and dust were predominant. Discussion Spring is the travel season in Lijiang, and the higher tourism activity contributes to the change in EC concentration. In Mar., fireworks and burning during the Naxi Festival in the region cause a high EC concentration. In addition, westerly air currents carry dust from the West Asian Desert, which causes dust pollution. In this region, the contributions of biomass and coal combustion sources to babs are much greater than those of dust and traffic sources. Before Apr. 22, the proportion of the contribution of biomass combustion was the largest; however, after that date, the contribution of dust increased in proportion, resulting in a significantly higher babs in early spring compared with late spring. The char-EC/soot-EC ratio was greater than 1 for all observations, and the backward trajectory clustering results indicated that in this region is most strongly affected by biomass combustion, which mainly comes from the long-distance transmission of EC from India, Nepal, and Myanmar on the westerly airflow. Conclusions The spring EC concentration in the southeastern margin of the Tibetan Plateau is mainly affected by biomass combustion and dust. Biomass combustion is compounded by long-distance transport from Southeast Asia (northeastern Myanmar) and local anthropogenic emissions, whereas dust pollution is from long-distance transport from Southeast Asia. Recommendations and perspectives This study provides a reference for understanding the environmental status of the Tibetan Plateau and data on the air pollutants that are driving climate change in the Tibetan Plateau region. |
| Key words: elemental carbon (EC) Tibetan Plateau positive definite matrix factorization (PMF) backward
trajectories |
