Single photon laser-induced fluorescence detection of no and so₂ for atmospheric conditions of composition and pressure

Reported here are laboratory results from a laser-induced fluorescence (LIF) study of the molecules NO and so₂ in which both the selectivity and sensitivity of the LIF method are examined. The laser excitation of these molecules occurred at 226 and 222 nm, respectively. The laser system employed consisted of a Nd:YAG-driven Quanta-Ray PDL dye laser, the fundamental of which was frequency doubled, and this output, in turn, was then frequency mixed with the Nd:YAG fundamental at 1064 nm. Two different dyes were required for generating the 226- and 222-nm wavelengths. To make these results as relevant as possible to the ultimate development of an atmospheric airborne field sampling system all experiments were carried out in atmospheric conditions of pressure and composition. In addition to the experimental data provided there has also been presented a theoretical assessment of the signal strength for both the NO and so₂ LIF systems, and these results have been compared with the experimentally measured values. Current state-of-the-art technology would suggest that both NO and SO2 can be measured by the LIF technique in atmospheric conditions at concentration levels of a few pptv.