The optical depolarizing properties of simulated stratospheric aerosols were studied in laboratory laser (0.633 μm) backscattering experiments for application to polarization lidar observations. Clouds composed of sulfuric acid solution droplets, some treated with ammonia gas, were observed during evaporation. The results indicate that the formation of minute ammonium sulfate particles from the evaporation of acid droplets produces linear depolarization ratios of δ ≈ 0.02, but δ ≈ 0.10–0.15 are generated from acid droplet crystallization effects associated with recycled aerosols and the introduction of ammonia gas into the chamber. It is concluded that partially crystallized sulfuric acid droplets are a likely candidate for explaining the lidar δ ≈ 0.10 values that have been observed in the lower stratosphere in the absence of the relatively strong backscattering from homogeneous sulfuric acid droplet (δ ≈ 0) or ice crystal (δ ≈ 0.5) clouds.
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