Condensation of HNO₃ and HCl in the winter polar stratospheres

TLDR

Nitric acid and hydrochloric acid vapors may condense in the winter polar stratospheres. On PSC surfaces, ClO, N₂O₅, and ClNO₃ react to produce additional HNO₃, HCl, and HOCl, while sedimentation can remove these species from the stratosphere. Nitric acid clouds would form at PSC temperatures with optical depths matching observations, indicating HNO₃ dominates PSCs; nearby reactions could deplete NOₓ, potentially enabling halogen chemistry to generate the ozone hole.

Abstract

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.