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

NO_x（NO+NO_2）对大气中光化学臭氧（O3）的产生起着重要作用。本研究针对飞行器测量中NO_2的检测问题，研制了一套NO_2检测系统，由于NO_2检测系统已经研制成功，因此将NO_2转化为NO的紫外光解系统是该系统的关键。我们使用金属卤素灯作为光源。我们还使用了一个光解池，其壁涂有反射铝，以增加在细胞中的光解速率。我们还开发了一种聚四氟乙烯阀来控制光解池内的压力。结果，在电池内的停留时间为1-2秒时，获得约50%的转化效率。当电池内的压力保持较高时，转换效率可以更高，但是发现其他分子如N_2O_5也被光解。此外，在波长小于320 nm的紫外光下，应使用滤光片进行滤光，以防止HNO_3的光解。在此基础上，我们计划研制一种可用于机载的NO_2探测系统。

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.