Trace detection of atmospheric NO_2 by laser-induced fluorescence using a GaN diode laser and a diode-pumped YAG laser

摘要

We report on the development of a highly sensitive detection system for measuring atmospheric NO_2 by means of a laser-induced fluorescence (LIF) technique at 473 nm using a diode-pumped Nd:YAG laser. A GaN-based laser diode emitting at 410 nm is also used as an alternative fluorescence-excitation source. For laboratory calibrations, standard NO_2 gas is diluted with synthetic air and is introduced into a fluorescence-detection cell. The NO_2 LIF signal is detected by a photomultiplier tube and processed by a photon-counting method. The minimum detectable limits of the NO_2 instrument developed have been estimated to be 0.14 ppbv and 0.39 ppbv (parts per billion, 10~(-9), by volume) in 60 s integration time (signal-to-noise ratio of 2) for 473 and 410 nm excitation systems, respectively. Practical performance of the instrument has been demonstrated by the 24 hour continuous measurements of ambient NO_2 in a suburban area.