QEPAS based ppb-level detection of CO and N2O using a high power CW DFB-QCL

摘要

An ultra-sensitive and selective quartz-enhanced photoacousticspectroscopy (QEPAS) sensor platform was demonstrated for detection ofcarbon monoxide (CO) and nitrous oxide (N2O). This sensor used a stateof-the art 4.61 μm high power, continuous wave (CW), distributed feedbackquantum cascade laser (DFB-QCL) operating at 10°C as the excitationsource. For the R(6) CO absorption line, located at 2169.2 cm−1, a minimumdetection limit (MDL) of 1.5 parts per billion by volume (ppbv) atatmospheric pressure was achieved with a 1 sec acquisition time and theaddition of 2.6% water vapor concentration in the analyzed gas mixture. Forthe N2O detection, a MDL of 23 ppbv was obtained at an optimum gaspressure of 100 Torr and with the same water vapor content of 2.6%. Inboth cases the presence of water vapor increases the detected CO and N2OQEPAS signal levels as a result of enhancing the vibrational-translationalrelaxation rate of both target gases. Allan deviation analyses wereperformed to investigate the long term performance of the CO and N2OQEPAS sensor systems. For the optimum data acquisition time of 500 sec aMDL of 340 pptv and 4 ppbv was obtained for CO and N2O detection,respectively. To demonstrate reliable and robust operation of the QEPASsensor a continuous monitoring of atmospheric CO and N2O concentrationlevels for a period of 5 hours were performed.