Characterization of H₂S QEPAS detection in methane-based gas leaks dispersed into environment

The increase in fatal accidents and chronic illnesses caused by hydrogen sulfide (H₂S) exposure occurring in various workplaces is pushing the development of sensing systems for continuous and in-field monitoring of this hazardous gas. We report here on the design and realization of a Near-IR quartz-enhanced photoacoustic sensor (QEPAS) for H₂S leaks detection. H₂S QEPAS signal was measured in matrixes containing up to 1 % of methane (CH₄) and nitrogen (N₂) which were chosen as the laboratory model environment for leakages from oil and gas wells or various industrial processes where H₂S and CH₄ can leak simultaneously. An investigation of the influence of CH₄ on H₂S relaxation and photoacoustic generation was proposed in this work and the sensor performances were carefully assessed with respect to CH₄ content in the mixture. We demonstrated the high selectivity, with no cross talk between H₂S, H₂O and CH₄ absorption lines, high sensitivity, and fast response time of the developed sensor, achieving a minimum detection limit (MDL) of 2.5 ppm for H₂S with 2 s lock-in integration time. The employed 2.6 µm laser allowed us to employ the sensor also for CH₄ detection, achieving an MDL of 85 ppm. The realized QEPAS sensor lends itself to the development of a portable and compact device for industrial monitoring.