Abstract
An infrared absorption spectrometer called SPIRIT (SPectromètre Infra-Rouge In situ Toute altitude) has been developed for airborne measurements of trace gases in the troposphere. At least three different trace gases can be measured simultaneously every 1.6 s using the coupling of a single Robert multipass optical cell with three Quantum Cascade Lasers (QCLs), easily interchangeable to select species depending on the scientific objectives. Absorptions of the mid-infrared radiations by the species in the cell at reduced pressure (<40 hPa), with path lengths adjustable up to 167.78 m, are quantified using an HgCdTe photodetector cooled by Stirling cycle. The performances of the instrument are assessed: a linearity with a coefficient of determination R2 > 0.979 for the instrument response is found for CO, CH4, and NO2 volume mixing ratios under typical tropospheric conditions. In-flight comparisons with calibrated gas mixtures allow to show no instrumental drift correlated with atmospheric pressure and temperature changes (when vertical profiling) and to estimate the overall uncertainties in the measurements of CO, CH4, and NO2 to be 0.9, 22, and 0.5 ppbv, respectively. In-flight precision (1σ) for these species at 1.6 s sampling is 0.3, 5, and 0.3 ppbv, respectively.
Highlights
IntroductionIn recent years, infrared laser absorption spectroscopy has been successful for atmospheric measurements of small
In recent years, infrared laser absorption spectroscopy has been successful for atmospheric measurements of smallFor more than 20 years, our group, in collaboration with the French space agency CNES (Centre National d’Etudes Spatiales), has developed a series of balloon-borne instruments using optical spectroscopy techniques with remote or in situ light sources for the detection of stratospheric species [18,19,20]
We present a newly built airborne instrument called SPIRIT (SPectromètre Infra-Rouge In situ Toute altitude)
Summary
In recent years, infrared laser absorption spectroscopy has been successful for atmospheric measurements of small. SPIRIT is not designed for long-term greenhouse gas monitoring to be reported onto known global calibration scale (e.g., WMO/GAW network) This monitoring can be conducted by commercially available instruments (e.g., Picarro Inc., Los Gatos Research Inc., Aerodyne Research Inc.) and needs regular in-flight calibrations [7, 8, 10, 13] at the expense of valuable ambient acquisition such as sudden unexpected increases in abundances of species. In-flight calibrations are possible essentially for stable greenhouse gases and CO using embarked cylinders, but more difficult to handle with reactive or sticky species Besides these commercial spectrometers, developing and implementing home-made instruments such as the one presented here are valuable. This leads to a complete independent mastering of the process for data acquisition and molecular concentration retrievals, and enables immediate diagnosis and swift repair in case of failure during field campaigns
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