Development of an SO2 monitor for mobile sources

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Development of an SO2 monitor for mobile sources

Burch, D.E. / Davila, P.S. / Gates, F.J. / Pembrook, J.D.

An instrument has been designed and built to monitor the concentration of SO2 in the exhaust of mobile sources. A grating assembly disperses the ultraviolet energy from a deuterium-arc source and passes five narrow spectral intervals. Three of the intervals (set A) coincide with strong absorption features in the SO2 band near 3000 A;the other two intervals (set B) coincide with weak absorption. A spinning reticle alternately transmits energy passing through set A and B to a photomultiplier detector. A dc output signal proportional to the concentration of SO2 in the sample cell is produced by appropriate electronics. A pump and manifold assembly permit operation over a wide range of sample flow rates. At high flow rates, the 90 % sample turn-over time is approximately 0.7 sec. The sample cell contains a multiple-pass optical system adjusted to 12 passes, giving a sample path length greater than 5 m. The rms noise level corresponds to approximately 0.05 ppm of SO2 when the electronic time constant is 1 sec. (DePo)