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A-2.1.2 Study on the origin of methylbromide by radio carbon isotope measurement

[Contact Person]

Masatoshi Morita
Director, Regional Environment Division
National Institute for Environmental Studies
Environment Agency
16-2 Ongoawa, Tsukuba, Ibaraki 305-0053, Japan
Phone +81-298-50-2332, Fax +81-298-50-2570

Total Budget for FY1996-FY1998

26,909,000 Yen (FY 1998: 7,858,000 Yen)

Abstract

To determine the origin of methylbromide (MeBr) in the atmosphere, C-14 dating method using accelerator mass spectrometry (AMS) is being attempted. Two large-volume samplers for the collection of methylbromide in the atmosphere, including a transportable system based on a silica gel pre-water trap, several water trap systems and a methylbromide trap by molecular sieve-type active carbon cooled by dry ice, and a pump for high volume sampler, were constructed and their performances were evaluated. A small SIM peak corresponding to methylbromide was detected in the collected samples, though the absolute amount was not enough for the AMS ¹⁴C measurement. Further purification of this fraction is being attempted by the combination of a cooled injection system (CIS) and a preparative capillary gas chromatography (PCGC). Attempts were also made for two orders reduction of necessary amount of samples for the AMS measurement. Reduction by one order was attained by the present graphitization system with data correction based on the standard produced under the same condition (same carbon/iron catalyst ratio). An additional order reduction was attempted by constructing a new graphitization system with much smaller volume of reaction chamber.

[Key Words]

Methylbromide, carbon dating by AMS