Actual cloud particles contain on the order of millions of molecules. VERA's clusters consist of three to 30 molecules. The presence of polar stratospheric clouds is key to the ozone-depleting chemical reactions that take place above the pole. Each spring, the ozone concentration above Antarctica drops by about half. Air trapped in the beaker becomes extremely cold during the night.
Temperatures drop low enough to form clouds even in the very dry stratosphere.
These clouds provide the necessary surface for a series of ion-molecule reactions. This, in the formof chlorine nitrate and hydrochloric acid, dissolves on the cloud surfaces to form chlorine ions. There, the ions react to form more active chlorine species. These active molecules don't destroy ozone immediately, but lie dormant until the polar night lifts and spring sunshine breaks them down into aggressive chlorine atoms. Ordinarily, as Mereand explains, these atoms would be bound up by nitrogen compounds present in the atmosphere, as part of a natural atmospheric equilibrium, and returned to an inert state.