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