LITES-based methane isotope ratio measurement and source attribution

This work presents what we believe to be the first application of light-induced thermoelastic spectroscopy (LITES) to methane isotope detection, demonstrating the development of a compact, low-power system. By targeting the near-infrared absorption lines of the two isotopologues ¹³CH₄ and ¹²CH₄ and applying Kalman filtering, the system simultaneously measures their absolute concentrations and isotopic abundance ratio while achieving improved signal-to-noise performance. Experimental validation with chemically synthesized methane and biogas from a wastewater treatment plant demonstrates that the isotopic ratios obtained are in excellent agreement with high-precision mass spectrometry, allowing reliable discrimination of methane sources. This study establishes LITES as a promising approach for portable, low-power, and in situ isotope monitoring.