Condensation of HNO₃ and HCl in the winter polar stratospheres

Nitric acid and hydrochloric acid vapors may condense in the winter polar stratospheres. Nitric acid clouds, unlike water ice clouds, would form at the temperatures at which polar stratospheric clouds (PSCs) are observed and would have optical depths of the magnitude observed suggesting that HNO 3 is a dominant component of PSCs. ClO, N 2 O 5 and ClNO 3 may react on cloud particle surfaces yielding additional HNO 3 , HCl, and HOCL. In the vicinity of PSCs these reactions could deplete the stratosphere of photochemically active NO x species. The sedimentation of PSCs may remove these materials from the stratosphere. The loss of vapor phase NO x might allow halogen‐based chemistry to create the ozone hole.