DESIGN OF EXTRA CAVITY PHOTOACOUSTIC SPECTROMETER BASED ON BLUE DIODE LASER IN NO2 (NITROGEN DIOXIDE) GAS DETECTION

Background: NO2 detection is necessary because NO2 is an air pollutant causing photochemical smog and acid rain. In addition, respiratory diseases are caused by high levels of NO2 in the inhaled air. Aim: The purpose of this study was to detect NO2 using PAS utilizing Arduino Uno, an easy, simple, and low-cost research. Methods: The detection of Nitrogen Dioxide (NO2) gas with a Photoacoustic Spectrometer (PAS) using an Arduino Uno microcontroller has been carried out. The PAS system uses a blue diode laser with a wavelength of 450 nm as the radiation source because this wavelength is suitable for NO2 gas. The intensity of the laser beam is modulated using a modulation system with an on-off scheme using the Arduino Uno. The modulation frequency has been varied to get the maximum detection frequency. The photoacoustic cell used was a single resonator photoacoustic cell with type H. Sound sensor and photodiode were used in this measurement. The amplification of the signal was done by utilizing the Lock-in amplifier, and the constant time of Lock-in amplifier was also determined to optimize the PAS. Nitrogen gas was used to detect background signal. Results and Discussion: From the photoacoustic spectrometer optimization, the results obtained were a laser diode frequency of 1,000 Hz with a duty cycle of 50% and a Lock-in amplifier amplification of 10,000 times with a constant time of 3.3 ms. The maximum concentration reached in this measurement was 6 ppm. The background signal achieved in this measurement was 0.00002 V/W. The lowest detection limit achieved in this measurement was 0.0064 ppm.Conclusion: The gas sample containers containing NO2 with larger sizes tend to have a greater concentration. Sometimes, the NO2 concentration of the large sample gas container was overtaken by the small sample container.