Depletion of stratospheric ozone allows larger doses of harmful solar UV radiation to reach the surface leading to increases in skin cancer and cataracts in humans and other impacts, such as crop damage. Ozone also affects the Earth's radiation balance and, in particular, ozone depletion in the lower stratosphere (LS) exerts an important climate forcing. While most long-lived ozone-depleting substances (e.g. CFCs) are now controlled by the United Nations Montreal Protocol and their abundances are slowly declining, there remains significant uncertainty surrounding the rate of ozone layer recovery. Changes in the LS may cause delayed ozone recovery or even additional depletion, and can also have important effects on climate. One key uncertainty, highlighted in recent WMO/UNEP Assessments of Stratospheric Ozone Depletion (2014, 2018, 2022, is the increasing importance of uncontrolled chlorine-containing very short-lived substances (VSLS) which can reach the LS and cause ozone depletion.

The SISLAC project was a collaboration between the universities of Leeds, Lancaster and East Anglia (UEA). The project built on the UEA's heritage in atmospheric halocarbon measurements to obtain novel observations of chlorine compounds in the key E/SE Asia region and in the global mid-upper troposphere. Surface observations targeted in the key winter periods when polluted emissions from China were detected, a likely major emitter of Cl-VSLS globally.

The observations were interpreted using simulations of the TOMCAT 3-D chemical transport model at Leeds and Lancaster. Results of a standard simulation are archived here; further specific experiments are referenced from relevant publications.

This project was funded by Natural Environment Research Council (NERC) grant reference: NE/R001782/1.