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A ppb-level mid-IR quartz-enhanced photoacoustic sensor for the highly sensitive detection of dimethyl methyl phosphonate (DMMP) —the sarin simulant—is developed using a T-shaped tuning fork. The sensor employs a narrow-linewidth mid-IR quantum cascade laser (QCL) to target a strong, interference-free DMMP absorption band. A custom quartz tuning fork with 800-μm prong spacing is employed to avoid significant photothermal noise, thus removing the requirement for an optical spatial filter. The performance of the photoacoustic sensor was optimized in terms of exciting power, modulation frequency, and gas pressure. A minimum detection limit of 6 ppb was achieved at an integration time of 300 ms, which can be further improved to 0.45 ppb at the optimal integration time of 20 s • A ppb-level photoacoustic sensor for the sarin simulant detection was developed. • A large-gap-spacing quartz tuning fork was used to decrease noise. • A minimum detection limit of 0.45 ppb was achieved at an optimal integration time of 20 s. • The high selectivity of the sensor was verified in a real environment. [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]

• A QEPAS-based sensor with V-T relaxation self-calibration was developed. • A dual-gas detection was realized based on two-mode combined vibration of a QTF. • A self-calibration method for the CH 4 V-T relaxation was provided. • The ppb-level self-calibration CH 4 sensor has a simple setup and small sensor size. • Continuous measurements near a landfill in Shanxi province, China, were performed. A quartz-enhanced photoacoustic spectroscopy methane (CH 4) sensor with vibrational to translational (V-T) relaxation self-calibration was realized and tested for atmospheric CH 4 detection near a landfill. To normalize the influence of H 2 O vapor on the CH 4 energy relaxation rate, CH 4 and H 2 O concentrations were detected simultaneously by means of a frequency division multiplexing technique, in which a custom quartz tuning fork was operated in the fundamental and first overtone combined vibration mode. A continuous wave, thermoelectrically cooled distributed feedback interband cascade laser emitting at 3.3 μm and a near-infrared DFB laser emitting at 1.37 μm were used as the excitation source for CH 4 and H 2 O detection, respectively. A theoretical model of V-T relaxation and self-calibration method were developed to allow this CH 4 sensor to have a simple setup and a small sensor size. Continuous field measurements were carried out near the largest sanitary landfill in Shanxi province, China, to demonstrate the stability and ruggedness of the realized CH 4 sensor. [ABSTRACT FROM AUTHOR]