Atmospheric CH4 measurement near a landfill using an ICL-based QEPAS sensor with V-T relaxation self-calibration

A quartz-enhanced photoacoustic spectroscopy methane (CH4) sensor with vibrational to translational (V-T) relaxation self-calibration was realized and tested for atmospheric CH4 detection near a landfill. To normalize the influence of H2O vapor on the CH4 energy relaxation rate, CH4 and H2O 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, thermo-electrically cooled distributed feedback interband cascade laser emitting at 3.3 mu m and a near-infrared DFB laser emitting at 1.37 mu m were used as the excitation source for CH4 and H2O detection, respectively. A theoretical model of V-T relaxation and self-calibration method were developed to allow this CH4 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 CH4 sensor.