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 ( CO2 ) concentrations using a non-dispersive infrared analyzer
carried by a small helium-filled balloon ( CO2 sonde) has been
developed for the first time. Vertical profiles of atmospheric CO2 can
be measured with a 240–400 m altitude resolution through regular onboard
calibrations using two different CO2 standard gases. The standard
deviations ( 1σ ) of the measured mole fractions 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. Two CO2 
vertical profile data obtained using the CO2 sondes, which were
launched on 31 January and 3 February 2011 at Moriya, were compared
with the chartered aircraft data on the same days and the commercial
aircraft data obtained by the Comprehensive Observation Network for TRace
gases by Airliner (COTRAIL) program on the same day (31 January) and 1 d before (2 February). The difference between the CO2 sonde data
and these four sets of in situ aircraft data (over the range of each balloon
altitude ±100  m) up to the altitude of 7 km was 0.6±1.2  ppm
(average ±1σ ). In field experiments, the CO2 sonde
detected an increase in CO2 concentration in an urban area and a
decrease in a forested area near the surface. The CO2 sonde was shown
to be a useful instrument for observing and monitoring the vertical profiles
of CO2 concentration in the troposphere.