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Measurement of 14C Concentrations of Stratospheric CO2 by Accelerator Mass Spectrometry

Published online by Cambridge University Press:  18 July 2016

Toshio Nakamura ,
Takakiyo Nakazawa ,
Nobuyuki Nakai ,
Hiroyuki Kitagawa ,
Hideyuki Honda ,
Tomizo Itoh ,
Toshinobu Machida  and
Eiji Matsumoto
Toshio Nakamura
Affiliation:
Dating and Materials Research Center, Nagoya University, Nagoya 464-01 Japan
Takakiyo Nakazawa
Affiliation:
Faculty of Science, Tohoku University, Sendai 980 Japan
Nobuyuki Nakai
Affiliation:
Department of Earth Sciences, Nagoya University
Hiroyuki Kitagawa
Affiliation:
Water Research Institute, Nagoya University
Hideyuki Honda
Affiliation:
Institute of Space and Astronautical Science, Sagamihara 229 Japan
Tomizo Itoh
Affiliation:
Institute of Space and Astronautical Science, Sagamihara 229 Japan
Toshinobu Machida
Affiliation:
Faculty of Science, Tohoku University, Sendai 980 Japan
Eiji Matsumoto
Affiliation:
Water Research Institute, Nagoya University
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Abstract

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In order to measure the concentrations of anthropogenically influenced gases in the stratosphere, we have collected air samples from the lower stratosphere since 1985, by a balloon-borne cryogenic sampling method, developed at the Institute of Space and Astronautical Science (ISAS). Air samples of ≃16 liters at STP were collected in the stratosphere at altitudes from 18.6 to 30.4 km, over the northeastern part of Japan (39.5°N, 139–142°E), on 1 September 1989. We conducted 14C analyses to study the vertical and horizontal air-mass movement in the stratosphere, and to investigate the air transport mechanism between troposphere and stratosphere. Carbon dioxide (containing a few mg carbon) was separated cryogenically from the air samples, and the 14C concentration of the CO2 was measured by a Tandetron accelerator mass spectrometer, using Fe-graphite targets prepared by reducing CO2 on Fe-powder with hydrogen in a Vycor tube at 650°. The 14C concentrations, expressed as Δ14C, of CO2 were 267–309‰ at altitudes of 21–30 km, and 134‰ at 19–20 km. The Δ14C values at 21–30 km were higher than those of the current tropospheric CO2, of around 80–200‰. The observed 14C concentrations, higher in the stratosphere than the troposphere, seem to be explained by large bomb-produced 14C inventories and/or high 14C production by cosmic rays, as well as weak vertical mixing of air masses in the stratosphere.

Type
III. Global 14C Production and Variation
Information
Radiocarbon , Volume 34 , Issue 3: Proceedings of the 14th International Radiocarbon Conference , 1992 , pp. 745 - 752
Copyright
Copyright © The American Journal of Science 

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