Calibrated remote measurements of SO2 and O3 using atmospheric backscatter

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Abstract
Remote measurements of calibrated samples of SO2 and O3 have been achieved with a lidar using ultraviolet signals produced by a tunable dye laser and a nonlinear crystal. The operating wavelengths for these measurements were 292.3 and 293.3 nm for SO2 and 292.3 and 294.0 nm for O3. The atmosphere in front of and behind the chamber acted as a distributed reflector to send laser light back through the chamber to a receiver near the laser. The laser measurements agreed well with in situ measurements. Integration of eight laser pulses at each of two wavelengths allowed the determination of SO2 concentration with an uncertainty equivalent to ±0.6 ppm in 100 m for low concentrations. For O3, the corresponding uncertainty limit was ±1.2 ppm in 100 m. The measurement errors are primarily attributable to variations in atmospheric backscattering intensity during the experiment, since the different wavelengths were radiated sequentially rather than simultaneously. The sensitivity of a system transmitting more favorable wavelengths at intervals separated by less than 1 min is estimated to be near ±0.1 ppm in 100 m for both SO2 and O3.