Laser Spectroscopy Sensor for Measurements of Trace Gaseous Sulfur Dioxide (SO[subscript 2])

Abstract

Laser induced fluorescence (LIF) using non tunable laser sources is a method which has been studied for the measurement of atmospheric sulfur dioxide (SO₂). As this approach is direct, there is no need of sample collection or sample concentration and the air sample can be used directly for analysis. In the approach used in these studies, a Nd:YAG laser operating at 266 nm, which is the fourth harmonic of this non-tunable laser, is used as an excitation source. Other wavelengths of excitation at 199 nm, 217 nm and 223 nm can also be used and are produced by stimulated raman scattering (SRS) of 266 nm and 355 nm radiation in compressed hydrogen gas. Studies of the analytical capability of these LIF approaches have been performed at different laser wavelengths. Studies of the fluorescence spectrum signal power dependence, linearity and sensitivity have been performed. The best results have been obtained using excitation at 223 nm resulting in a limit of detection of 0.01 ppm. With further development, it is expected that the LIF approach may be able to perform fast, sensitive measurements of SO₂ in the open environment while avoiding many of the interferences that occur in the conventional methods for SO₂ measurements.