Intercomparison of two cavity ring-down spectroscopy analyzers for atmospheric <sup>13</sup>CO<sub>2</sub>  ∕ <sup>12</sup>CO<sub>2</sub> measurement

Abstract

Abstract. Isotope ratio infrared spectroscopy (IRIS) permits continuous in situ measurement of CO 2 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 CO 2 δ 13 C analyzers (G1101-i and G2201-i (newer version)) and evaluated their performance and comparability. The best precision was 0.08-0.15 ‰ for G1101-i and 0.01-0.04 ‰ for G2201-i. The dependence of δ 13 C on CO 2 concentration was 0.46 ‰ per 100 ppm and 0.09 ‰ per 100 ppm, the instrument drift ranged from 0.92-1.09 ‰ and 0.19-0.37 ‰, and the sensitivity of δ 13 C to the water vapor mixing ratio was 1.01 ‰ / % H 2 O and 0.09 ‰ / % H 2 O 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 ‰ for G1101-i and −0.13-0.03 ‰ for G2201-i. The sensitivity of δ 13 C to the water vapor mixing ratio improved from 1.01 ‰ / % H 2

Calibration of isotopologue-specific optical trace gas analysers: a practical guide

“…Several groups have reported on ratio calibration schemes and the consequent concentration dependence (e.g. Griffith et al, 2012;Wen et al, 2013;Rella et al, 2015;Pang et al, 2016;Braden-Behrens et al, 2017;Flores et al, 2017). The concentration dependence inevitably follows if the actual calibration relationships between measured and true amounts of individual isotopologues (Sect.…”

“…Several studies have addressed isotopic calibration (e.g. Esler et al, 2000;Bowling et al, 2003;Griffis et al, 2005;Mohn et al, 2008;Loh et al, 2011;Tuzson et al, 2011;Griffith et al, 2012;Wehr et al, 2013;Wen et al, 2013;Rella et al, 2015;Vardag et al, 2015;Pang et al, 2016;Flores et al, 2017;Tans et al, 2017;Braden-Behrens et al, 2017) and compared calibration approaches (Wen et al, 2013), but until recently most studies made some level of approximation in dealing with the calculations required to properly include the contributions of all possible isotopologues of the target species in the calculation scheme. Most recently Griffith et al (2012), Flores et al (2017) and Tans et al (2017) have published isotopic calibration strategies which are equivalent and which correctly and completely account for the full isotopic composition of the target gas (CO 2 in these studies, but applicable in principle to any species).…”

Measuring 13C‐enriched CO2 in air with a cavity ring‐down spectroscopy gas analyser: Evaluation and calibration

“…To apply our calibration strategy to raw G2131-i measurement data (using either our non-linear model or a normal linear equation for 12 CO 2 ), a post-correction workbook is supplied (S4, supporting information). While calibration constants may vary temporally and between individual G2131-i analysers, given the minimal drift and inter-instrument consistency observed in other studies, 9,22,65 we expect that reasonable accuracy may be achieved by cautious application of our correction model to measurements of 13 C-enriched CO 2 samples by other G2131-i units. In any case, the results and methods reported here are a template for G2131-i users and may be extended to other laser absorption instruments sharing the same CO 2 spectroscopy (e.g.…”

“…Corrections are generally accomplished by one-point offsets or two-point interpolations, and standards are chosen that are as close as possible to unknown sample values. 31 The principal errors that calibrations of δ 13 C-CO 2 measurements usually address are concentration dependence and instrument drift; 22 unknown sample values are adjusted precisely, and final uncertainties typically derive from measurement precision rather than from uncertainties on standards. 9 In the present study, we faced a different set of considerations.…”

Pollution Events at the High-Altitude Mountain Site Zugspitze-Schneefernerhaus (2670 m a.s.l.), Germany

“…Notably, this analyzer was not upgraded to account for the spectral interferences caused by methane (bias δ 13 C by 0.4% CH 4 ppm −1 ) and water vapor (including water vapor dilution, water vapor pressure broadening, and HDO spectral interference effects). Several studies have evaluated and validated the G1101-i analyzer measurements before and after upgrading in comparison with other measurement devices [4,[36][37][38][39][40]. As described by Ghasemifard et al [4], the measured CO 2 and δ 13 C were post-corrected, in which parallel measured CO 2 , H 2 O, and CH 4 were employed.…”