Abstract. We assess the performance of an Isotope Ratio Infrared Spectrometer (IRIS) to measure carbon (δ¹³C) and oxygen (δ¹⁸O) isotope ratios in atmospheric carbon dioxide (CO₂) and report observations from a 26 day field deployment trial at Baring Head, New Zealand, NIWA's atmospheric observatory for Southern Ocean baseline air. Our study describes an operational method to improve the performance in comparison to previous publications on this analytical technique. By using a calibration technique that reflected the principle of identical treatment of sample and reference gases, we achieved a reproducibility of 0.07 ‰ for δ¹³C-CO₂ and 0.06 ‰ for δ¹⁸O-CO₂ over multiple days. This performance is within the "extended compatibility goal" of 0.1 ‰ for both δ¹³C-CO₂ and δ¹⁸O-CO₂, which was recommended by the World Meteorological Organisation (WMO) for studies of regional or urban CO₂ fluxes. One goal of this study was to assess the capabilities and limitations of the IRIS analyser to resolve δ¹³C-CO₂ and δ¹⁸O-CO₂ variations under field conditions. Therefore, we selected multiple events within the 26 day record for Keeling Plot Analysis. This resolved the isotopic composition of end members with an uncertainty of ≤ 1 ‰ when the magnitude of CO₂ signals is larger than 10 ppm. The uncertainty of the Keeling Plot Analysis strongly increased for smaller CO₂ events (2–7 ppm), where the instrument performance is the limiting factor and may only allow for the distinction between very different end members, such as the role of terrestrial versus oceanic carbon cycle processes. Further improvement in measurement performance is desirable to meet the WMO "network compatibility goal" of 0.01 ‰ for δ¹³C-CO₂ and 0.05 ‰ for δ¹⁸O-CO₂, which is needed to resolve the small variability that is typical for background air observatories such as Baring Head.

中文翻译：

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IRIS 分析仪评估揭示了新西兰南大洋大气观测站 Baring Head 二氧化碳同位素比率的亚小时变化

摘要。我们评估了同位素比红外光谱仪 (IRIS) 测量大气二氧化碳 (CO ₂ ) 中碳 (δ ¹³ C) 和氧 (δ ¹⁸ O) 同位素比的性能，并报告了在巴林进行的 26 天现场部署试验的观察结果负责人，新西兰，NIWA 南大洋基线空气大气观测站。我们的研究描述了一种操作方法，与之前关于此分析技术的出版物相比，可以提高性能。通过使用反映样品和参考气体相同处理原理的校准技术，我们实现了 δ ¹³ C-CO ₂ 0.07 ‰和 δ ¹⁸ O-CO ₂ 0.06 ‰的再现性经过多天。该性能在 δ ¹³ C-CO ₂和 δ ¹⁸ O-CO ₂ 0.1 ‰的“扩展兼容性目标”内，这是世界气象组织 (WMO) 推荐用于区域或城市 CO ₂通量研究的。本研究的一个目标是评估 IRIS 分析仪在现场条件下解析 δ ¹³ C-CO ₂和 δ ¹⁸ O-CO ₂变化的能力和局限性。因此，我们选择了 26 天记录中的多个事件进行 Keeling 图分析。这解决了不确定度≤ 1 ‰ 当 CO ₂信号大于 10 ppm。对于较小的 CO ₂事件 (2–7 ppm)，Keeling 图分析的不确定性大大增加，其中仪器性能是限制因素，并且可能只允许区分非常不同的终端成员，例如陆地与海洋的作用碳循环过程。需要进一步改进测量性能以实现 WMO 的“网络兼容性目标”，即 δ ¹³ C-CO ₂为 0.01 ‰，δ ¹⁸ O-CO ₂为 0.05 ‰ ，这是解决背景典型的小变化所必需的空中天文台，如 Baring Head。