Abstract
Abstract. Tunable diode laser absorption (TDL) and cavity ring-down spectroscopic (CRDS) sensors for atmospheric carbon dioxide were co-deployed during summer and fall of 2010 in field and laboratory conditions at Los Alamos National Laboratory. Both sensors were characterized for accuracy and precision for ambient carbon dioxide measurements at ground level and compared using both laboratory and ambient field data. After post-processing that included water vapor correction and calibration to WMO reference standards, overall mean [12C16O2] = 392.05 ± 8.92 ppm and [12C16O2] = 392.22 ± 9.05 ppm were observed between 29 July and 16 August 2010. The mean difference between the CRDS and TDL data for 12CO2 was 0.04 ± 1.80 ppm (±1σ in 60 s) for ambient field data, demonstrating the sensors meet the WMO/IAEA compatibility standard. The observations show over the 19-day period the [CO2]CRDS'/[CO2]TDL ratio exhibits a Gaussian distribution centered at x0 = 1.003 ± 3.38 × 10−5 (±1σ), indicating the ratio is dominated by random noise as opposed to a bias in the output of either sensor. The CRDS sensor is capable of measuring [12C16O2] to a precision of 23 ppb in 1 min and decreases to 6.5 ppb in 58 min. At one and 58-min, the TDL exhibits precisions of 29 ppb and 53 ppb. The CRDS is compact, fast, and stable; the TDL is larger and requires frequent calibrations to maintain its precision. The sensors also exhibit consistent hourly averaged diurnal values underscoring the interplay of biological, anthropogenic, and transport processes regulating CO2 at the site.
Highlights
Sensors based on optical spectroscopy are important tools for rapid, accurate in situ measurements of greenhouse gases for biosphere-atmosphere flux estimates and source attribution applications
Low, and unknown gases was performed for 16 h and output for the cavity ringdown absorption analyzer (CRDS) and tunable diode laser absorption (TDL) sensors were averaged to 1 min time constants
The calibration factor is based on reference standards known to a higher precision and wider concentration range than previously used by our group for the CRDS sensor
Summary
Sensors based on optical spectroscopy are important tools for rapid, accurate in situ measurements of greenhouse gases for biosphere-atmosphere flux estimates and source attribution applications. Numerous laser-based sensors are undergoing rapid development to study greenhouse gases, it is important to conduct instrument inter-comparisons to establish their compatibility under field conditions. We inter-compare a commercially available cavity ringdown absorption analyzer (CRDS) with a commercially available tunable diode laser absorption (TDL) system for monitoring carbon dioxide [12C16O2]. Both the CRDS and TDL sensors are used throughout the climate and ecosystem research and environmental sensing communities and it is important to directly compare the results of laser-based optical absorption sensors operating via related principles but different techniques to ensure data sets from either sensor are in agreement with reference standards and each other
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