Studies of polar stratospheric cloud formation

Stratospheric ozone depletion was first reported in 1985. Early on, researc hers identified polar stratospheric clouds (PSCs) as being important in che mistry related to ozone depletion. PSCs exist as crystalline water-ice part icles (type IT), 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.