An Evaluation of Calibration Techniques for In Situ Carbon Dioxide Measurements Using a Programmable Portable Trace-Gas Measuring System

Abstract

The construction and deployment of a portable trace-gas measurement system (TGaMS) is described. The air-collection system (dubbed HYDRA) collects air samples from 18 different locations and was connected to either one or two LI-COR LI-7000 gas analyzers to measure CO 2 . An in situ ''field calibration'' method, that uses four calibration gases with an uncertainty on the order of 60.1 mmol mol 21 relative to the WMO CO 2 mole fraction scale, revealed CO 2 output from the LI-7000 had a slightly nonlinear relationship relative to the CO 2 concentration of the calibration gases. The sensitivity of the field-calibrated CO 2 to different forms of the field-calibration equation is investigated. To evaluate TGaMS performance, CO 2 from collocated inlets, portable gas cylinders, and nearby independent CO 2 instruments are compared. Results are as follows: 1) CO 2 measurements from HYDRA multiple inlets are feasible with a reproducibility of 60.4 mmol mol 21 (based on the standard deviation of the CO 2 difference between collocated inlets when HYDRA was operating with two LI-7000s); 2) CO 2 differences among the various field-calibration equations were on the order of 60.3 mmol mol 21 ; and 3) comparison of midday hourly CO 2 measurements at 30 m AGL between TGaMS and an independent high-accuracy CO 2 measurement system (within 300 m of TGaMS) had a median difference and standard deviation of 0.04 6 0.81 mmol mol 21 over two months.

Atmospheric Stability Effects on Wind Fields and Scalar Mixing Within and Just Above a Subalpine Forest in Sloping Terrain

“…Additional CO 2 measurement systems added for CME04 were: an Autonomous Inexpensive Robust CO 2 analyzer (AIRCOA; Stephens et al (2006)) at Aspen and Willow towers and the Trace Gas Measurement System (TGaMS; Burns et al (2009)) at the Pine tower (see Table 2 for the details of each CO 2 system). The above-canopy midday χ c median difference (and standard deviation) between the AIRCOA at Aspen and TGaMS was 0.04 ± 0.81 µmol mol −1 over 2 months ).…”

Atmospheric CO<sub>2</sub> monitoring with single-cell NDIR-based analyzers

“…However, it is important to describe and report the performance of current NDIR systems because (1) data from these systems are supporting a wide range of analyses and publications (Obrist et al, 2008;Burns et al, 2009;De Wekker et al, 2009;CarbonTracker, 2010;Burns et al, 2011;Strong et al, 2011;Brooks et al, 2011), (2) a number of these systems are still operating in the field and will continue to do so for years to come, and (3) systems like these may still find favor over laser-based systems in applications where initial cost is a priority, and (4) many of the gas-handling, sample drying, calibration, and intercomparison issues we discuss are relevant to any atmospheric CO 2 measurement system regardless of sensor type.…”

The Niwot Ridge Subalpine Forest US-NR1 AmeriFlux site – Part I: Data acquisition and site record-keeping

“…plexer (model AM416). The MRS CR10 logger was used to measure vertical snow temperature profiles (e.g., Burns et al, 2013).…”

“…measurement system (Burns et al, 2009) used in multiple experiments at the site (e.g., Monson et al, 2006;Oncley et al, 2009;Sun et al, 2010). This software is included within the Supplement (USNR1_opto22.zip).…”