LIF Detection of NO2 Using a CW Diode Laser Combined with a Supersonic Jet

Atmospheric NO2 is detected by LIF with a sensitivity of 300 pptv/ 10 sec (S/N = 2) using a cw laser combined with a supersonic expansion. A 16 mW tunable diode laser (640 nm at 1 MHz linewidth) is used to excite a single rotational feature in first excited electronic state of NO2. A cw supersonic expansion cools the NO2 to approximately 25 K enhancing the population in the rotational level we excite and increasing the signal by a factor of 20. The supersonic jet is maintained by a compact pumping system utilizing an automobile supercharger backed by a rotary oil pump. The complete system is small and operates autonomously for days to weeks. Data from a ground-based campaign in Granite Bay, California from July 16 through September 15, 2001, including an inter-comparison with our dye laser based LIF instrument operating at 585nm will be described.