半導体レーザー吸収分光法の自動車排気中の二酸化炭素炭素同位体比計測への応用

抄録

A high-sensitivity laser absorption spectroscopic technique has been employed for measurements of the stable carbon isotope ratio of carbon dioxide (CO₂), ¹³CO₂/¹²CO₂, in automobile exhaust. The amounts of ¹²CO₂ and ¹³CO₂ were detected through wavelength modulation spectroscopy using a distributed feedback laser diode in the 2-μm wavelength region. A 0.15-L one-pass optical cell with an effective optical path length of 0.5 m was used for continuous measurements of automobile exhaust, with the intention of maintaining the residence time to less than 5 s. In addition, a 0.9-L Herriott-type multi-pass optical cell with an effective optical path length of 29.9 m was used for precise measurements of the stable carbon isotope ratio of CO₂ in automobile exhaust, which was collected in a sampling bag. Continuous measurements of the stable carbon isotope ratio were performed with a reproducibility of 0.28 ‰ (1σ) in 14.8 % CO₂ for every 1-s signal measurement without signal integration over an 1830 s period. The feasibility of the developed system was evaluated for continuous measurements of the CO₂ stable carbon isotope ratio in automobile exhaust. Resultantly, we successfully performed continuous measurements of the stable carbon isotope ratio of CO₂ in automobile exhaust and found that the stable carbon isotope ratio of CO₂ changed in accordance with the driving conditions.