Development of a balloon-borne instrument for CO 2 vertical profile observations in the troposphere

Abstract. A novel, practical observation system for measuring tropospheric carbon dioxide (CO 2 ) concentrations using a non-dispersive infrared analyzer carried by a small helium-filled balloon (CO 2 sonde), has been developed for the first time. Onboard calibrations, using CO 2 standard gases, is possible to measure the vertical profiles of atmospheric CO 2 accurately with a 240–400 m altitude resolution. The standard deviations (1σ) of the measured mixing ratios in the laboratory experiments using a vacuum chamber at a temperature of 298 K were approximately 0.6 ppm at 1010 hPa and 1.2 ppm at 250 hPa. Compared with in situ aircraft data, although the difference up to the altitude of 7 km was 0.6 ± 1.2 ppm, this bias and difference were within the precision of the CO 2 sonde. In field experiments, the CO 2 sonde detected an increase in CO 2 concentration in an urban area and a decrease in a forested area near the surface. The CO 2 sonde was shown to be a useful instrument for observing and monitoring the vertical profiles of CO 2 concentration in the troposphere.