光腔衰荡光谱技术测定大气水汽稳定同位素校正方法研究

doi:10.3964/j.issn.1000-0593(2019)06-1700-06

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Abstract Nearly every small gas-phase molecule (e. g., H₂O, CO₂) has a unique near-infrared absorption spectrum. At sub-atmospheric pressure, each tiny gas-phase molecule has a one-to-one characteristic spectral line. Based on this principle, it can use the Isotope Ratio Infrared Spectroscopy (IRIS) to accurately analyze the isotopic composition of gas samples, which overcomes the limitations of the conventional Isotope Ratio Mass Spectrometry (IRMS) and has become a recognized high-precision, high-sensitivity and high-accuracy method for trace-gas detection. In recent years, commercial laser spectroscopy gas composition analysis technology has gradually developed, and more and more scholars have made significant progresses in their respective fields using laser spectroscopy instruments. Among them, especially the study of atmospheric water vapor stable isotope has important significance to the study of hydrological cycle process. Laser spectroscopy makes it possible to conduct continuous and in-situ high-resolution measurement of atmospheric water vapor stable isotope (δ¹⁸O and δD). However, its observational precision and accuracy are affected by factors such as the operating characteristics, the sensitivity of different concentrations of atmospheric water vapor to specific spectral absorbance and so on, usually leading to the observations with obvious nonlinear response problems. Therefore, it is necessary to calibrate various deviations during the process of instrument observation. But at this stage, many users are not yet clear about the international calibration methods for the new observational technology. Therefore, based on Wavelength-Scanned Cavity Ring-Down Spectroscopy (WS-CRDS) technology, the atmospheric water vapor isotope observation system (Picarro L2120-i)measures the ring-down time at different wavelengths by Tunable Diode Laser (TDL) emitting laser of different wavelengths that can be absorbed by the target gas and that cannot be absorbed by the gas. And then by analyzing the ring-down time difference of the sample absorption and without any gas absorption, it can calculate molecular concentration of the target gas with high precision, and then determine the water vapor stable isotope composition. This paper establishes a set of accurate and reliable observation procedures and calibration methods in respect to memory effect, drift effect, concentration effect and so on, which provides a reference for researchers who are using or will use such equipment to obtain high-precision and high-reliability atmospheric water vapor stable isotope observation data.

Key words：WS-CRDS; Water vapor stable isotope; Calibration methods

Received: 2018-04-02 Accepted: 2018-09-08

ZTFLH:

O657.3

Corresponding Authors: PANG Hong-xi E-mail: hxpang@nju.edu.cn

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https://www.gpxygpfx.com/EN/10.3964/j.issn.1000-0593(2019)06-1700-06 OR https://www.gpxygpfx.com/EN/Y2019/V39/I06/1700