Development of a Stable Carbon Isotopes Analysis Instrument Based on Tunable Diode Laser Absorption Spectroscopy

Abstract

A compact laser spectrometry instrument was developed for high precision measurements of isotope ratio of CO₂ by tunable diode laser absorption spectroscopy in the mid-infrared at 2.7 μm. The experimental spectrum of carbon isotopologues in the gas phase near 3641 cm⁻¹ is very suitable for real-time analysis of these isotopologues. Simultaneous measurements of the mixing ratio and the corresponding δ¹³C values of CO₂ in the atmosphere were performed. The achieved standard deviation (1σ) of δ¹³C was 1.8‰. The Allan analysis of the time series of the mixing ratio of CO₂ shows a measurement precision of 0.2‰ for δ¹³C with an optimum integration time of about 130 s. The spectrometer is capable of real-time measurements of stable carbon isotope ratios of CO₂ under ambient conditions.