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• Quartz-Enhanced Photoacoustics for sensitive and selective hydrocarbon detection. • Shoe box sized (sizes 30 cm × 10 cm × 20 cm) QEPAS sensors deployable for real-time and in-situ gas analysis. • Methane, ethane minimum detection limit of 90 ppb and 7 ppb at 1 sec of integration time, respectively. • Propane detected down to 3 ppm at 1 sec of integration time. • 13CH4 and 12CH4 isotopes detected with a 13δ <10‰ at 0.1 sec of integration time. Quartz-enhanced photoacoustic spectroscopy represents a valuable candidate for natural gas analysis in the oil & gas field. The core element of this spectroscopy technique is a quartz tuning forks, employed as high quality-factor optoacoustic transducers, capable of operating in a wide range of temperatures and pressures. The robustness and compactness of these sensors, together with the possibility to avoid the use of optical detectors, open the way to the development of a new generation of small-sized gas spectrometers to be potentially employed downhole for source rock characterization and estimation of oil & gas properties. We report here on the realization of a shoe-box sized quartz-enhanced photoacoustic spectroscopy system capable of: i) selective detection of methane and ethane in the parts-per-billion range, and propane in the parts-per-million range, by employing a single interband cascade laser emitting at 3.345 µm; ii) selective detection of 12CH 4 and 13CH 4 isotopes at the parts-per-billion sensitivity level by employing a quantum cascade laser operating around 7.73 µm. [ABSTRACT FROM AUTHOR]

We demonstrated a 19-inches 6U-rack sensing system based on quartz-enhanced photoacoustic spectroscopy for simultaneous detection of methane, nitrous oxide, and ammonia in atmosphere. The system embeds two detection modules, each one equipped with a quantum cascade laser as light source and a spectrophone composed of a T-shaped quartz tuning fork coupled with acoustic resonator tubes. The sensing system results compact, lightweight, and portable, with a computer interface for an easy end-user operation. The calibration was performed in laboratory environment with certified concentrations. Because of the NH 3 large and permanent dipole moment, ammonia QEPAS signal was used to model and characterize adsorption/desorption processes, for an accurate and reliable sensor calibration. At 0.1 s signal integration time, detection limits of 28 ppb, 9 ppb, and 6 ppb were obtained for CH 4 , N 2 O, and NH 3 , respectively. Since these detection limits were well below the natural abundance of the three analytes in atmosphere, the sensor was employed to monitor CH 4 , N 2 O, and NH 3 concentrations in laboratory air. • Development of a compact 19-inches 6U-rack QEPAS sensor box for simultaneous detection of CH 4 , N 2 O, and NH 3 in atmosphere. • Minimum detection limits of 28.0 ppb, 9 ppb and 6 ppb at 0.1 s integration time for CH 4 , N 2 O and NH 3 detection, respectively. • Sensor tested by analysing ambient air. Mean concentrations of ∼ 1.81 ppm of CH 4 , 329 ppb of N 2 O and 83 ppb of NH 3 measured. [ABSTRACT FROM AUTHOR]