| 摘要: |
| 本文对北京市和厦门市大气CO2及 δ13C进行观测，研究内陆城市和沿海城市CO2浓度及 δ13C的季节和昼夜变化规律及影响因素，以期为政府制定碳减排政策提供科学依据。北京市和厦门市CO2浓度均呈现秋冬季高于春夏季，而 δ13C秋冬季低于春夏季，季节差异原因可能是秋冬大气边界层降低，化石燃料消耗增加，贫13C的CO2气体大量排放。观测期间，两个城市日变化模式均表现为CO2夜间高于白天， δ13C夜间低于白天；且在早晚交通高峰时段，两地CO2浓度均有不同程度升高，而 δ13C有不同程度降低。冬季，北京市由于受西、北部高山阻挡，在东南风条件下使得其夜间大气CO2浓度显著增高， δ13C值则显著降低。根据两地新增CO2的 δ13C值（δs）推测，北京市受到煤炭燃烧贡献较大，厦门市季节差异较大，推测受植物排放CO2速率及气象条件等共同影响。 |
| 关键词: 大气 CO2 浓度 δ13C 季节变化 昼夜变化 Keeling 曲线 |
| DOI：10.7515/JEE182029 |
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| 基金项目:国家自然科学基金项目（41573136，41773141）；中国科学院“西部之光”（XAB2014A02）；中国科学院青年创新促进会（2016360） |
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| Variational characteristics of CO2 concentrations and δ13C values at the urban sites in Beijing and Xiamen, China |
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FENG Xue, WANG Sen, NIU Zhenchuan
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1. College of Urban and Environmental Sciences, Northwest University, Xi’an 710127, China
2. Shaanxi Key Laboratory of Earth Surface System and Environmental Carrying Capacity, Northwest University, Xi’an 710127, China
3. State Key Laboratory of Loess and Quaternary Geology, Institute of Earth Environment, Chinese Academy of Sciences, Xi’an 710061, China
4. Xi’an Accelerator Mass Spectrometry Center, Xi’an 710061, China
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| Abstract: |
| Background, aim, and scope To mitigate the global warming, more and more attention of the environmental scientists are focused on atmospheric CO2 increase. Urban areas are hotspots of anthropogenic CO2 emission sources. It is necessary to monitor the feature of CO2 variations in urban areas. The data of CO2 concentration and the stable carbon isotope ratio (δ13C) are important for CO2 reduction in urban areas. Therefore, the variation in CO2 and δ13C in urban areas are observed in this paper. The study presented the data of atmospheric CO2 concentrations and δ13C values at the urban sites in the inland city of Beijing and in the coastal city of Xiamen, to study the seasonal and diurnal variation in CO2 concentration and δ13C during 2014, and their key factors. Materials and methods In this study, we measured the CO2 concentration and its δ13C at the urban sampling sites in Beijing and Xiamen, respectively. Beijing is a typical inland city, which is located in the northwest of the North China Plain, surrounded by West Mountain and Jundu Mountain. It is the center of the Beijing-Tianjin-Hebei metropolitan region, with a population of more than 20 million. Xiamen is one of the cities in southeast coastal areas, facing the Taiwan Strait, with a resident population of more than 4 million. There is no direct pollution sources around the sampling sites in Beijing and Xiamen. We used aluminum foil sampling bags to collect the air samples and collected 144 urban air samples in this study. The CO2 concentrations and δ13C of samples were measured by the Picarro G2131-Ⅰ CO2 Isotopic Analyzer (Picarro Inc.) with cavity ring down spectroscopy (CRDS). This analyzer has a characteristic of highly linearity and accuracy in CO2 and δ13C measurements (error < 0.1‰). The CO2/ and δ13C value for each sample was measured for 6 minutes, and the average of the data from the last 4 min was used, to avoid equipment instability created by dead volumes when switching a new sample. Results The results showed that the CO2 concentrations in Beijing and Xiamen were high in fall and winter, and low in spring and summer, but the C values are low in fall and winter, and high in spring and summer during the period of our study. Diurnal observations at the urban sites in Beijing and Xiamen showed low CO2 concentrations and high δ13C values in the daytime, while high CO2 concentrations and low δ13C values in the night. Additionally, morning and afternoon rush hour peaks were observed. Discussion The sampling site in Beijing and Xiamen displayed much higher CO2 increase and lower δ13C values than the background site of Waliguan. The obvious difference of CO2 concentration and δ13C values between sampling site and background station may be from the influence of regional emission, so it is necessary to analyze the regional emission sources. Keeling plot method by the additional stable carbon isotope ratio produced by a local source (δs) showed that the increased CO2 in Beijing is mainly affected by coal combustion. The δs in Xiamen was influenced by fossil fuel like coal and oil in summer, and the reduction of respiration of plants and the change of weather condition during winter is the main reason for the variation in δs in Xiamen. Conclusions The reason for the variation atmospheric CO2 in the inland city of Beijing and the coastal city of Xiamen were influenced by multivariate factors such as emission sources, height of the vertical mixing, wind direction and topography. Recommendations and perspectives Using stable carbon isotope technology can understand the main sources of increased atmospheric CO2, but there is still some uncertainty. 14 C tracing was needed to further quantify the fossil source CO2 in the future. |
| Key words: atmospheric CO2 concentration stable carbon isotope seasonal variation diurnal variation Keeling plot |
