Measurements of the Concentrations of CO_2,CH_4 and N_2O and the Carbon Isotopic Ratio of CH_4 in the Stratosphere Using a Balloon-borne Cryogenic Sampler
Stratospheric air samples have been collected over Japan during the period from 1985 to 1995 using a balloon-borne cryogenic sampler, and then analyzed for the CO_2,CH_4 and N_2O concentrations and the carbon isotopic ratio of CH_4. The results showed that the CO_2 concentration decreased with height in an interval from the tropopause to 20-25km, and then became almost constant values above this level. The concentration differences between the lowermost part of the stratosphere and heights above 20-25km amounted to 4-8 ppmv. The lower stratospheric CO_2 showed different profiles for different measurements, probably due to annually- and seasonally-dependent poleward air transport and vertical mixing of stratospheric air near the jet stream. An average increase rate of the stratospheric CO_2 concentration was estimated to be 1.50 (±0.04) ppmv/year from the data above 20-25km. The CH_4 and N_2O concentrations decreased rapidly from about 1750 and 311 ppbv at the tropopause to 550-900 and 30-70 ppbv at 35km, respectively, due to their strong destruction through photolysis and chemical reactions. δ^<13>C value of CH_4 increased markedly with height, from -47‰ just above the tropopause to about -39‰ at 35km, which is quite opposite to the vertical profile of the CH_4 concentration. It was strongly suggested that the destruction of CH_4 by the reaction with Cl atoms is responsible for this steep vertical profile of δ^<13>C.
気球搭載クライオサンプリング装置を用いた成層圏大気中の CO_2,CH_4,N_2O の濃度と CH_4 の炭素同位体比の測定
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