Sub-ppb level photoacoustic spectroscopy NOx sensor using a low cost 455 nm laser diode

Highly sensitive NO_x (NO and NO₂) sensors are used in a wide range environmental, industrial and human health applications. In this work, a dual-gas NO_x sensor based on photoacoustic spectroscopy (PAS) was developed. A low cost 455 nm laser diode was used as excitation source. NO was converted to NO₂ by the O₃ titration reaction, thus enabling indirect detection. Periodic control of NO_x and NO₂ passing through the photoacoustic cell using solenoid valves. The concentration of NO was then calculated from the difference between the measured NO_x and NO₂. Sub-ppb level detection limit of 0.2 ppb was obtained for NO₂ with 1 s integration time. Measurement precision was further improved using a weighted Kalman filtering algorithm. The performance of the developed sub-ppb level PAS NO_x sensor was demonstrated by comparing ambient NO_x measurements with a commercial chemiluminescence analyzer, which showed good agreement between them over four consecutive days of measurements. The PAS NO_x sensor developed in this work has great potential for the development of economical high sensitivity NO_x sensors.