A development of photolysis system for NO_2 measurement on board the aircraft

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NO_x (NO+NO_2) plays a critical role on the phtochemical ozone (03) production in the troposhere. In this study, a prototype system for NO_2 detection has been developed for a future application on the aircraft measurement.The UV Photolysis system to convert NO_2 into NO is the key of the instrument, beause the NO detection system has been already developed. We have used a metal halogen lamp as a light source. We have also used a photolysis cell of which wall was coated with reflective aluminum to increase the photolysis rate in the cell. We have also developed a Teflon valve to control a pressure inside the photolysis cell. As a result, a conversion efficiency of about 50% was obtained with a residence time inside of the cell of 1-2 sec. A conversion efficiency can be higher when pressure inside the cell is kept higher, however other molecules such as N_2O_5 was found to also be photodissociated. In addition, Uv in the wavelength shorter than 320nm should be cut using optical filter to prevent the photodissociation of HNO_3. Based on these results, we plan to develop a NO_2 detection system which can be used on board the aircraft.