Asynchronous changes of CO2, H2, and He concentrations in soil gases: A theoretical model and experimental results

Abstract

This paper focuses on the chemical composition changes in soil gases through both a theoretical model and laboratory experiments. The model describes the one-dimensional mass transfer process, which is triggered by changes in the flux parameters of the system, and the time-dependent evolution of the composition of the soil gases as a function of (i) the pristine gas mixture, (ii) the diffusivity of the chemicals, and (iii) the thickness of the transited medium. Carbon dioxide (CO2), hydrogen (H2), and helium (He) were used in a laboratory-scale flux simulator to investigate the evolution of the gas composition profile in an artificial soil of constant thickness. The agreement between the theoretical calculations and the experimental results supports the validity of the model. Our results indicate a good reproducibility of the transient changes in the concentrations of CO2, He, and H2 in CO2-rich gas mixtures that contain He and H2 as trace gases. Finally, the theoretical results were used to analyze the H2 and CO2 continuous monitoring data collected at Etna volcano in 2010.