Studies of polar stratospheric cloud formation.

Stratospheric ozone depletion was first reported in 1985. Early on, researchers identified polar stratospheric clouds (PSCs) as being important in chemistry related to ozone depletion. PSCs exist as crystalline water-ice particles (type II), and as crystalline (type Ia) or liquid (type Ib) particles stable above the water-ice frost point. Uncertainty remains concerning the composition and formation mechanism of the most common PSC, type Ia. Here, we consider likely formation mechanisms for type Ia PSCs.