Type I polar stratospheric clouds

Borrmann, S S. Solomon, J. E. Dye, D. Baumgardner, K. K. Kelly, and K. R. Chan, Heterogeneous Reactions on Stratospheric Background Aerosols, Volcanic Sulfuric Acid Droplets, and Type I Polar Stratospheric Clouds Effects of Temperature Fluctuations and Differences in Particle Phase, J. Geophys. Res., 102, 3639-3648 (1997b). 

Ravishankara, A. R., and D. R. Hanson, Differences in the Reactivity of Type I Polar Stratospheric Clouds Depending on Their Phase, J. Geophys. Res., 101, 3885-3890 (1996). 

Tabazadeh, A., R. P. Turco, K. Drdla, and M. Z. Jacobson, A Study of Type I Polar Stratospheric Cloud Formation, Geophys. Res. Lett., 21, 1619-1622 (1994a). 

Leu, M.-T., Moore, S.B., Keyser, L.L. Heterogeneous reactions of chlorine nitrate and hydrogen chloride on type I polar stratospheric clouds. J. Phys. Chem. 95, 7763-7771 (1991)... 

Polar stratospheric clouds have been classified into two broad types, so-called Type I and Type II (Table 4.1). Type I PSCs have been further subdivided into Type la and Type Ib. Type la PSCs have traditionally been identified as crystals of nitric acid trihydrate, HNO, 3 H2O, denoted NAT, that form once temperatures fall below about 195 K. Type lb PSCs consist of supercooled ternary solutions of HNO3/H2SO4/H2O, also forming at about the same temperature threshold. Type II PSCs are largely frozen water ice, nonspherical crystalline particles, that form at temperatures below the ice frost point. The ice frost point, for example, at 3 X 10 Torr H O is 191 K. Despite the above classification, the composition of PSCs is still uncertain (Toon and Tolbert, 1995). 

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