Intercomparison of two cavity ring-down spectroscopy analyzers for atmospheric 13CO2 12CO2 measurement

• Published in: Atmospheric measurement techniques 2016-08, Vol.9 (8), p.3879-3891
• Main Authors: Pang, Jiaping, Wen, Xuefa, Sun, Xiaomin, Huang, Kuan
• Format: Article
• Language: English
• Subjects: Analytical methods; Analyzers; Calibration; Carbon dioxide; Cavity ringdown; Correlation; Diurnal; Diurnal cycle; Diurnal variations; Fourier transforms; Gases; In situ measurement; Infrared analysis; Infrared spectroscopy; Instruments; Intercomparison; Isotope composition; Isotope ratios; Isotopes; Laboratories; Lasers; Measurement; Measurement techniques; Mixing ratio; Performance evaluation; Scientific imaging; Sensitivity; Software; Spectroscopic analysis; Studies; Valves; Water vapor; Water vapour
• ISSN: 1867-1381; 1867-8548
• DOI: 10.5194/amt-9-3879-2016

Isotope ratio infrared spectroscopy (IRIS) permits continuous in situ measurement of CO2 isotopic composition under ambient conditions. Previous studies have mainly focused on single IRIS instrument performance; few studies have considered the comparability among different IRIS instruments. In this study, we carried out laboratory and ambient measurements using two Picarro CO213C analyzers (G1101-i and G2201-i (newer version)) and evaluated their performance and comparability. The best precision was 0.08-0.15 [per thousand] for G1101-i and 0.01-0.04 [per thousand] for G2201-i. The dependence of 13C on CO2 concentration was 0.46 [per thousand] per 100 ppm and 0.09 [per thousand] per 100 ppm, the instrument drift ranged from 0.92-1.09 [per thousand] and 0.19-0.37 [per thousand], and the sensitivity of 13C to the water vapor mixing ratio was 1.01 [per thousand] % H2O and 0.09 [per thousand] % H2O for G1101-i and G2201-i, respectively. The accuracy after correction by the two-point mixing ratio gain and offset calibration method ranged from 0.04-0.09 [per thousand] for G1101-i and 0.13-0.03 [per thousand] for G2201-i. The sensitivity of 13C to the water vapor mixing ratio improved from 1.01 [per thousand] % H2O before the upgrade of G1101-i (G1101-i-original) to 0.15 [per thousand] % H2O after the upgrade of G1101-i (G1101-i-upgraded). Atmospheric 13C measured by G1101-i and G2201-i captured the rapid changes in atmospheric 13C signals on hourly to diurnal cycle scales, with a difference of 0.07 ± 0.24 [per thousand] between G1101-i-original and G2201-i and 0.05 ± 0.30 [per thousand] between G1101-i-upgraded and G2201-i. A significant linear correlation was observed between the 13C difference of G1101-i-original and G2201-i and the water vapor concentration, but there was no significant correlation between the 13C difference of G1101-i-upgraded and G2201-i and the water vapor concentration. The difference in the Keeling intercept values decreased from 1.24 [per thousand] between G1101-i-original and G2201-i to 0.36 [per thousand] between G1101-i-upgraded and G2201-i, which indicates the importance of consistency among different IRIS instruments.