Fully Integrated Photoacoustic NO(2) Sensor for Sub-ppb Level Measurement

A fully integrated photoacoustic nitrogen dioxide (NO(2)) sensor is developed and demonstrated. In this sensor, an embedded photoacoustic cell was manufactured by using an up-to-date 3D printing technique. A blue laser diode was used as a light source for excitation of photoacoustic wave in the photoacoustic cell. The photoacoustic wave is detected by a sensitive microelectromechanical system (MEMS) microphone. Homemade circuits are integrated into the sensor for laser diode driving and signal processing. The sensor was calibrated by using a chemiluminescence NO–NO(2)–NO(X) gas analyzer. And the performance of this sensor was evaluated. The linear relationship between photoacoustic signals and NO(2) concentrations was verified in a range of below 202 ppb. The limit of detection was determined to 0.86 ppb with an integration time of 1 s. The corresponding normalized noise equivalent absorption was 2.0 × 10(−8) cm(−1)∙W∙Hz(−1/2). The stability and the optimal integration time were evaluated with an Allan deviation analysis, from which a detection limit of 0.25 ppb at the optimal integration time of 240 s was obtained. The sensor was used to measure outdoor air and the results agree with that obtained from the NO–NO(2)–NO(X) gas analyzer. The low-cost and portable photoacoustic NO(2) sensor has a potential application for atmospheric NO(2) monitoring.