Impacts of Iodinated Very Short-Lived Substances on Stratospheric Ozone

The recovery of the stratospheric ozone layer faces increasing challenges from the rising emissions of unregulated very short-lived substances (VSLS). While the rapid increase in chlorinated VSLS, particularly dichloromethane (DCM), has been considered as a measurable threat to ozone recovery timelines, the potential risks posed by iodinated alternatives remain under-characterized. Although iodine emissions are largely natural, climate change may lead to a change in source strength. It is also important to quantify the impact of any possible anthropogenic sources. Finally, the interaction of iodine with other (decreasing) halogens may affect the efficiency of some chemical ozone loss mechanisms.

We investigate the potential impact on the stratospheric ozone layer of the several emission scenarios of iodinated VSLS. Model sensitivity experiments with a global 3-D chemical transport model TOMCAT show a strong dependence of ozone depletion on emission locations. Emissions in the wider tropics, or localised in southeastern Asia, give depletion 4-6 times that from emission in the mid-latitudes of the northern hemisphere. We will show ozone responses to the emissions in terms of polar ozone loss, and global total column trends. We will present our results in terms of ozone depletion potential (ODP) and a new metric, integrated ozone depletion (IOD). We will compare the results for iodine with the widely discussed chlorinated VSLS, DCM, and the long-lived ozone-depleting substance, CFC-11.