近赤外レーザー吸収分光法による大気中の二酸化炭素安定炭素同位体比連続計測装置の開発

概要

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A near-IR laser based spectrometer for continuous measurement of stable carbon isotopes in CO2 has been developed. 12CO2 and 13CO2 are detected with wavelength modulation spectroscopy and a Herriott-type multi-pass cell with a optical path length of 29.9 m using a distributed feedback laser diode in the 2-μm wavelength region. To measure the isotope ratio precisely, the influence of pressure and temperature variation in δ13C was evaluated. The limit of detection for 12CO2 in our system was 16 ± 1 ppbv. The precision in the determination of δ13C was 0.1‰ for 120 seconds signal integration time at ambient concentration levels. We demonstrate that our system enables automated continuous measurements of δ13C of CO2 in ambient air without any complex operation by users.