| 引用本文: | 侯瑶瑶，周卫健，程鹏，熊晓虎，周杰，吴书刚，杜花，卢雪峰，付云翀.2020.西安市2016 — 2017年大气化石源CO2的14C示踪研究与来源的初步分析[J].地球环境学报,11(1):90-98 |
| HOU Yaoyao, ZHOU Weijian, CHENG Peng, XIONG Xiaohu, ZHOU Jie, WU Shugang, DU Hua, LU Xuefeng, FU Yunchong.2020.Tracing study and source analysis of atmospheric fossil fuel CO2 by radiocarbon and air pollutants in Xi’an, China[J].Journal of Earth Environment,11(1):90-98 |
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| 西安市2016 — 2017年大气化石源CO2的14C示踪研究与来源的初步分析 |
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侯瑶瑶，周卫健，程鹏，熊晓虎，周杰，吴书刚，杜花，卢雪峰，付云翀
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1.中国科学院地球环境研究所 黄土与第四纪地质国家重点实验室，西安 710061
2.陕西省加速器质谱技术及应用重点实验室，西安加速器质谱中心，西安 710061
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| 摘要: |
| 14C是研究城市中化石能源碳排放状况的有效手段；认识化石源CO2（CO2ff）的主要来源将有利于针对性地制定减排方案。本文利用分子筛主动吸附采样方法对西安市大气CO2进行了连续积时采样，并利用AMS-14C示踪方法，研究了西安市2016—2017年 CO2ff的浓度变化，同时基于CO2ff与大气污染物的同源性，对CO2ff的主要来源进行了定性分析。2016年1月至2017年1月，西安大气Δ14C季节变化显著，变化范围是(−1.00±2.84)‰— (−187.25±3.62)‰，平均值为(−63.20±17.35)‰，相对于2012—2013年的平均值(−41.3±27.4)‰有明显的下降。CO2ff变化范围是(6.91±1.94)— (105.60±3.09) μmol∙mol−1，呈显著的夏季低、冬季高的季节变化特征，与前人研究结果一致。CO2ff与SO2及NO2浓度总体上呈相同的季节变化特征，但与两者的相关性存在季节差异：在春夏季，CO2ff与SO2（R2=0.47，p＜0.01）的相关性较强；而在秋冬季，CO2ff与NO2（R2=0.73，p＜0.01）的相关性更为显著。可能是由于大气扩散条件的改变使得采样点CO2ff的主要来源发生了变化。春夏季节，大气扩散条件较好，采样点化石源CO2可能主要受到工业燃煤（高空排放）的影响，而秋冬季节，受到不利于扩散的气象条件的影响，化石源CO2可能主要受到采样点周围交通源（近地面排放）的影响。该研究结果可为CO2ff的源解析研究及大气CO2样品采集提供参考。 |
| 关键词: AMS-14C示踪 分子筛 大气Δ14C 化石源CO2 季节变化 |
| DOI：10.7515/JEE192022 |
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| 基金项目:国家自然科学基金委项目（41730108）；大气重污染成因与治理攻关项目（DQGG0105-02） |
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| Tracing study and source analysis of atmospheric fossil fuel CO2 by radiocarbon and air pollutants in Xi’an, China |
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HOU Yaoyao, ZHOU Weijian, CHENG Peng, XIONG Xiaohu, ZHOU Jie, WU Shugang, DU Hua, LU Xuefeng, FU Yunchong
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1. State Key Laboratory of Loess and Quaternary Geology, Institute of Earth Environment, Chinese Academy of Sciences, Xi’an 710061, China
2. Shaanxi Key Laboratory of Accelerator Mass Spectrometry Technology and Application, Xi’an Accelerator Mass Spectrometry Center, Xi’an 710061, China
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| Abstract: |
| Background, aim, and scope Anthropogenic combustion of fossil fuel has emitted large quantities of CO2 to the atmosphere, which is closely related to global warming. More than 70% of global fossil fuel CO2 (CO2ff) emissions are concentrated in urban areas. Therefore, quantifying CO2ff, especially in the urban areas, is essential for us to formulate emission reduction strategies and understand earth’s carbon cycle. CO2ff contains no 14C because the half-life of 14C (5730 years) is much less than the age of fossil fuels. The difference between the 14C compositions of CO2 derived from fossil fuels and from modern CO2 sources is huge and this contrast makes 14C a unique tracer for quantifying CO2ff. Xi’an is the largest city in northwestern China. As the region’s energy consumption is dominated by fossil fuels, the city’s rapid development has consumed large amounts of fossil fuels. Thus, there is a need to understand the atmospheric CO2ff emission and its main source in Xi’an, China. Materials and methods In this study, we used self-designed active absorption system with a molecular sieve to continuously collect atmospheric CO2 samples from January 2016 to January 2017 in Xi’an. This active absorption system is based on the pressure gradient produced by the water flowing out of a glass bottle drop by drop. The samples were collected at a flow rate of 5 mL·min−1. When sampling finished, the molecular sieve device was inserted into the tube furnace and connected to the vacuum system with a metal joint to desorb and purify CO2 by cryogenic trapping. The purified CO2 was converted into graphite using the Zn-Fe method, in which Zn power is used as a reductant and Fe as a catalyst. The graphite was then pressed into an aluminum holder for 14C measurements using 3 MV accelerator mass spectrometer (AMS) in Xi’an, China, with a precision of 2‰ for 14C measurement. The atmospheric CO2 concentrations were measured using a Picarro G2131-i CO2 Isotopic Analyzer. Results From January 2016 to January 2017, the atmospheric Δ14C in Xi’an fluctuated significantly, ranging from (−1.00±2.84)‰ to (−187.25±3.62)‰; and the average is (−63.20±17.35)‰, which had a significant decline compared with the average value (−41.3±27.4)‰ during 2012—2013. The concentrations of CO2ff showed significantly seasonal variations, and varied from (6.91±1.94) μmol·mol−1 (July 2016) to (105.60±3.09) μmol·mol−1 (January 2017). The average concentration in winter ((53.22±11.78) μmol·mol−1) was significantly higher than that in summer ((15.16±6.63) μmol·mol−1). Discussion Based on the homology between CO2ff and air pollutants, we analyzed the relationships between CO2ff and air pollutants to figure out the main sources of CO2ff. The concentrations of CO2ff shared a similar trend over study period with air pollutants. However, the relationships between CO2ff and SO2/NO2 were different in different seasons. In spring and summer (from mid-March to August 2016), the concentrations of CO2ff showed stronge relationship with SO2 (R2=0.47, p<0.01), and had a weak correlation with NO2 (R2=0.28, p=0.02). In autumn and winter (from September 2016 to January 2017), the concentrations of CO2ff were strongly correlated with NO2 and SO2, but the correlation with NO2 was more significant (R2=0.73, p<0.01), and the correlation with SO2 was relatively weak (R2=0.46, p<0.01). This may be due to the different atmospheric diffusion conditions affected the contribution of industrial coal consumpution, which is maily from high-altitude point source (power plants), and the contribution of vehicles emissions to the CO2ff at sampling site. In spring and summer, atmospheric diffusion condition was conducive for vertical mixing and horizontal delivery of air pollutants, CO2ff at sampling site may be mainly affected by coal consumption emissions; in the autumn and winter, due to the adverse diffusion conditions, such as calm winds, the contribution of vehicle exhaust to CO2ff may significantly increase. Conclusions AMS-14C is an effective way to quantify CO2 emitted by fossil fuel consumption in cities. From January 2016 to January 2017, CO2ff concentrations showed significantly seasonal variations in Xi’an, with lowest values in summer and highest values in winter. By the relationships between CO2ff and air pollutants, this study qualitatively analyzed the main sources of CO2ff in different seasons. Due to the different atmospheric diffusion conditions, in spring and summer, CO2ff at the sampling site may be mainly affected by industrial coal combustion, while in autumn and winter, mainly by vehicles emissions. Recommendations and perspectivesThis study helps us to understand the seasonal variation characteristics of atmospheric CO2ff. And the homology between CO2ff and air pollutants will provide us a new idea for source analysis of CO2ff. Moreover, it’s important for us to select an appropriate sampling site in order to accurately analyse the impact of specific emission sources on CO2ff. |
| Key words: AMS-14C tracing molecular sieve atmospheric Δ14C fossil fuel CO2 seasonal variation |
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