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Tropospheric profiling of SO2 and O3 by multiwavelength DIAL

A multiwavelength differential absorption lidar (DIAL) system for measurement of trace atmospheric substances was developed. Vertical concentration profiles of SO 2 in the lower troposphere were measured by three wavelength dual-DIAL (on wavelength=300.05 nm, off wavelengths=299.35 nm, 300.90 nm, with null profiles obtained at 300.05 nm). The measurement wavelengths were chosen to minimize the effect of O 3 . Measurement results showed an average SO 2 concentration of 0.6 ppb for height 2000-4000 m, and the SO 2 measurement error was estimated to be about 1 ppb for 150 m range resolution. Although the measured SO 2 concentration was below the resolution of our system, the results show that the system is capable of measuring trace SO 2 with approximately 0.15 ppm-m resolution. In addition, vertical O 3 concentration profiles in the lower troposphere were measured using two identical DIAL pairs (on wavelength=285.0 nm, off wavelength=290.1 nm), from which two null profiles and two DIAL profiles were obtained simultaneously. The DIAL profiles, which showed an average O 3 concentration of 42 ppb for height 1000-4000 m, agree with simultaneous O 3 sonde measurements. The effect of backscatter gradients was shown to be small. The O 3 measurement error was estimated to be 3.4 ppb for 150 m range resolution, or about 0.5 ppm-m.