Sub-ppb nitrogen dioxide detection with a large linear dynamic range by use of a differential photoacoustic cell and a 3.5Â W blue multimode diode laser

A sub-ppb level photoacoustic spectroscopy (PAS)-based sensor for nitrogen dioxide (NO2) detection was developed by means of a 3.5 W CW multimode diode laser emitting at 447 nm. A differential photoacoustic cell was designed to match the imperfect laser beam and reduce the external acoustic as well as the electromagnetic noise. The diode laser power, gas flow and pressure of the sensor were optimized, which resulted in a NO2 sensor system with a detection limit of 54 pptv with a 1-s averaging time and an excellent linear dynamic range over > three orders of magnitude. The impact of water vapor as the catalyst on the photoacoustic signal amplitude was also investigated. Continuous measurements covering an eight-day period were performed to demonstrate the stability and robustness of the reported PAS-based NO2 sensor system.