The measurement of atmospheric <14>^CO concentration in Nagoya


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  • 名古屋における大気中<14>^CO濃度測定

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Atmospheric ^<14>CO can be used as a tracer of the global tropospheric hydroxyl radical (OH・). By reacting with many sorts of trace gases, such as methane (CH_4) and carbon monoxide (CO), the hydroxyl radical oxidizes and removes them from the atmosphere. It is expected that the behavior of hydroxyl radical is clarified by following that of CO, especially ^<14>CO. For collecting atmospheric CO, a preparation line was remodeled from a methane preparaton line. This line separates CO with other impurities from the air sample using cooled MS-5A. Carbon monoxide including the impurity is perfectly purified by the gas chromatography of the line. The purified CO is finally turned to carbon dioxide (CO_2) through the combustion tube in the line. However, only about 0.1-1ml of CO is included for 1m^3 air, it is not enough for ^<14>CO measurement by AMS (AMS required 1mg carbon or 2ml CO_2). Thus, the CO_2 derived from the CO in the air sample is diluted with the other CO_2 with known isotopic ratio. As show the Fig.1,the calculated value of ^<14>C/^<12>C isotopic ratio (R_<cal>) for the diluted sample are well agreed with that of neat CO_2 (R), where R is defined result of divide the ^<14>C/^<12>C ratio of the sample in ^<14>C/^<12>C ratio of the standard. The ^<14>CO and CO concentrations had been measured in Nagoya in winter. The results are shown in Fig.2. In spite of the CO concentration greatly fluctuating, it is proven that the ^<14>CO concentration increases in this period. As reported by Brenninkmeijer, the ^<14>CO concentraion has a maximum in winter and a minimum in summer in New Zealand and Antarctica (Brenninkmeijer 1993). The size and tendency in the fluctuation of the ^<14>CO concentration in Nagoya agrees with his report.


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