ABSTRACT
A quartz-enhanced photoacoustic absorption spectroscopy (QEPAS)-based gas sensor was developed for methane (CH4) and nitrous-oxide (N2O) detection. The QEPAS-based sensor was installed in a mobile laboratory operated by Aerodyne Research, Inc. to perform atmospheric CH4 and N2O detection around two urban waste-disposal sites located in the northeastern part of the Greater Houston area, during DISCOVER-AQ, a NASA Earth Venture during September 2013. A continuous wave, thermoelectrically cooled, 158 mW distributed feedback quantum cascade laser emitting at 7.83 µm was used as the excitation source in the QEPAS gas sensor system. Compared to typical ambient atmospheric mixing ratios of CH4 and N2O of 1.8 ppmv and 323 ppbv, respectively, significant increases in mixing ratios were observed when the mobile laboratory was circling two waste-disposal sites in Harris County and when waste disposal trucks were encountered.
ABSTRACT
A methane (CH4) and nitrous oxide (N2O) sensor based on a sensitive, selective and well established technique of quartz enhanced photoacoustic spectroscopy (QEPAS) was developed for environmental and biomedical measurements. A thermoelectrically cooled (TEC) distributed feedback quantum cascade laser (DFB-QCL), capable of continuous wave (CW) mode hop free emission in the 7.83 µm wavelength range, was used as an excitation source. For the targeted CH4 and N2O absorption lines located at 1275.04 cm(-1) and 1275.49 cm(-1) detection limits (1σ) of 13 ppbv and 6 ppbv were achieved with a 1 second data acquisition time, respectively. Environmental data of CH4 and N2O mixing ratios acquired using the QEPAS sensor system are also reported.
Subject(s)
Methane/analysis , Nitrous Oxide/analysis , Quantum TheoryABSTRACT
A system for gas sensing based on the quartz-enhanced photoacoustic spectroscopy technique has been developed. It makes use of a quantum well distributed feedback (DFB) laser diode emitting at 3.38 µm. This laser emits near room temperature in the continuous wave regime. A spectrophone, consisting of a quartz tuning fork and two steel microresonators were used. Second derivative wavelength modulation detection is used to perform low concentration measurements. The sensitivity and the linearity of the Quartz enhanced photoacoustic spectroscopy (QEPAS) sensor were studied. A normalized noise equivalent absorption coefficient of 4.06×10(-9) cm(-1)·W/Hz(1/2) was achieved.
