Voigt Claudia, Vallet-Coulomb Christine, Piel Clément, Alexandre Anne
Aix Marseille Univ, CNRS, IRD, INRAE, CEREGE, Aix-en-Provence, France.
ECOTRON Européen de Montpellier, UAR 3248, Centre National de la Recherche Scientifique (CNRS), Campus de Baillarguet, Montferrier-sur-Lez, France.
Rapid Commun Mass Spectrom. 2022 Mar 30;36(6):e9227. doi: 10.1002/rcm.9227.
Producing robust high-frequency time series of raw atmospheric water vapor isotope data using laser spectrometry requires accurate calibration. In particular, the chemical composition of the analyzed sample gas can cause isotope bias. This study assesses the matrix effect on calibrated δ O, δ O, δ H, O-excess, and d-excess values of atmospheric water vapor.
A Picarro L2140-i cavity ring-down spectrometer with an autosampler and a vaporizer is used to analyze δ O, δ O, δ H, O-excess, and d-excess of two water standards. Isotope data obtained using synthetic air and dry ambient air as carrier gas at water mixing ratios ranging from 2000 to 30 000 ppmv are compared. Based on the results, atmospheric water vapor measurements are calibrated. The expected precision is estimated by Monte Carlo simulation.
The dry air source strongly impacts raw isotope values of the two water standards but has no effect on the mixing ratio dependency functions. When synthetic air is used, δ O, δ O, and O-excess of calibrated atmospheric water vapor are overestimated by 0.6‰, 0.7‰, and 217 per meg, respectively, whereas δ H and d-excess are underestimated by 1.5‰ and 7.3‰. Optimum precisions for the calibrated δ O, δ O, δ H, O-excess, and d-excess values and 12 min integration time are 0.02‰, 0.03‰, 0.4‰, 14 per meg, and 0.4‰, respectively.
Regarding the obtained results, recommendations for the calibration of atmospheric water vapor isotope measurements are presented. The necessity to use dry ambient air as dry air source when running the standards for calibration is pointed out as a prerequisite for accurate atmospheric water vapor O-excess and d-excess measurements.
使用激光光谱法生成原始大气水汽同位素数据的稳健高频时间序列需要精确校准。特别是，被分析样气的化学成分会导致同位素偏差。本研究评估了基质对大气水汽校准后的δ¹⁸O、δ²H、δ¹⁶O、¹⁸O过剩和d过剩值的影响。
使用配备自动进样器和汽化器的Picarro L2140-i腔衰荡光谱仪分析两种水标准物质的δ¹⁸O、δ²H、δ¹⁶O、¹⁸O过剩和d过剩。比较了在2000至30000 ppmv的水汽混合比下，使用合成空气和干燥环境空气作为载气获得的同位素数据。基于这些结果，对大气水汽测量进行校准。通过蒙特卡罗模拟估计预期精度。
干燥空气源对两种水标准物质的原始同位素值有强烈影响，但对混合比依赖函数没有影响。当使用合成空气时，校准后的大气水汽的δ¹⁸O、δ²H和¹⁸O过剩分别被高估0.6‰、0.7‰和217‰，而δ¹⁶O和d过剩分别被低估1.5‰和7.3‰。校准后的δ¹⁸O、δ²H、δ¹⁶O、¹⁸O过剩和d过剩值以及12分钟积分时间的最佳精度分别为0.02‰、0.03‰、0.4‰、14‰和0.4‰。
根据所得结果，提出了大气水汽同位素测量校准的建议。指出在校准标准运行时使用干燥环境空气作为干燥空气源的必要性，这是准确测量大气水汽¹⁸O过剩和d过剩的前提条件。
