Abstract
Abstract. High-accuracy continuous measurements of greenhouse gases (CO2 and CH4) during the BARCA (Balanço Atmosférico Regional de Carbono na Amazônia) phase B campaign in Brazil in May 2009 were accomplished using a newly available analyzer based on the cavity ring-down spectroscopy (CRDS) technique. This analyzer was flown without a drying system or any in-flight calibration gases. Water vapor corrections associated with dilution and pressure-broadening effects for CO2 and CH4 were derived from laboratory experiments employing measurements of water vapor by the CRDS analyzer. Before the campaign, the stability of the analyzer was assessed by laboratory tests under simulated flight conditions. During the campaign, a comparison of CO2 measurements between the CRDS analyzer and a nondispersive infrared (NDIR) analyzer on board the same aircraft showed a mean difference of 0.22±0.09 ppm for all flights over the Amazon rain forest. At the end of the campaign, CO2 concentrations of the synthetic calibration gases used by the NDIR analyzer were determined by the CRDS analyzer. After correcting for the isotope and the pressure-broadening effects that resulted from changes of the composition of synthetic vs. ambient air, and applying those concentrations as calibrated values of the calibration gases to reprocess the CO2 measurements made by the NDIR, the mean difference between the CRDS and the NDIR during BARCA was reduced to 0.05±0.09 ppm, with the mean standard deviation of 0.23±0.05 ppm. The results clearly show that the CRDS is sufficiently stable to be used in flight without drying the air or calibrating in flight and the water corrections are fully adequate for high-accuracy continuous airborne measurements of CO2 and CH4.
Highlights
Efforts to measure the concentration of carbon dioxide (CO2) in the atmosphere to obtain the temporal and geographic distribution of atmospheric CO2 have been made since the 19th century (Callendar, 1940)
The results clearly show that the cavity ringdown spectroscopy (CRDS) is sufficiently stable to be used in flight without drying the air or calibrating in flight and the water corrections are fully adequate for high-accuracy continuous airborne measurements of CO2 and CH4
High-accuracy continuous measurements of greenhouse gases during the BARCA phase B campaign were achieved by an analyzer based on the cavity ring-down spectroscopy technique
Summary
Efforts to measure the concentration of carbon dioxide (CO2) in the atmosphere to obtain the temporal and geographic distribution of atmospheric CO2 have been made since the 19th century (Callendar, 1940). This analyzer is able to monitor atmospheric CO2 and CH4 of high accuracy without the need to dry the sample air or to employ in-flight calibrations. It was necessary to perform in-flight calibrations and careful air drying techniques in all previous in situ airborne measurements of CO2 and CH4 within the troposphere in order to guarantee measurement accuracy. The high performance and low maintenance of the CRDS analyzer has made it the choice as the analyzer for measurements of greenhouse gases on board a commercial airliner within a European Union project of In-service Aircraft for a Global Observing System (IAGOS).
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