Formation processes of upper tropospheric and polar stratospheric clouds and their ozone impacts

Ascertain the microphysical formation mechanisms of upper tropospheric clouds and polar stratospheric clouds and determine how modifications to polar stratospheric clouds influence stratospheric ozone depletion, in order to assess risks associated with stratospheric aerosol injection and to justify safety requirements that limit cloud-related chemical impacts.

Background

The paper notes that injected particles may serve as nuclei for cloud formation, particularly in regions where nuclei are rate-limiting, such as upper tropospheric cirrus and polar stratospheric clouds. Enhanced polar stratospheric cloud (PSC) formation could alter denitrification and extend polar ozone depletion, while cirrus modifications could affect radiative forcing.

Because the microphysical formation processes of these clouds and the consequent impact of PSC changes on ozone are not fully understood, the authors advocate conservative safety requirements. Closing these knowledge gaps is necessary to quantify and manage chemical and climatic risks from stratospheric aerosol injection.