Impact of chlorinated very-short-lived substances on stratospheric ozone (VSLS-MIP1)

Activity leaders

Ryan Hossaini
Lancaster University, UK

Lucy Carpenter
University of York, UK

Martyn Chipperfield
University of Leeds, UK

Doug Kinnison

Susann Tegtmeier
University of Saskatchewan, Canada

Activity description

Halogenated very short-lived substances (VSLSs) are defined as trace gases whose local lifetimes at the surface are shorter than 0.5 years. A large fraction of VSLS emissions are destroyed in the troposphere, yet they can make a significant contribution to stratospheric halogen levels, especially if emissions occur in regions with rapid transport to the stratosphere. Brominated and iodinated VSLSs are predominantly of natural oceanic origin, whereas chlorinated species have mostly anthropogenic emission sources. These chlorinated VSLSs are not controlled under the Montreal Protocol (MP), but have offset some of the Protocol’s benefits by slowing the rate of stratospheric chlorine removal (Hossaini et al., JGR, doi: 10.1029/2018JD029400, 2019). Thus, they have the potential to delay ozone layer recovery.

This VSLS community activity addresses many emerging and important issues concerning the impacts of VSLS on stratospheric ozone concentrations and trends. These issues warrant a comprehensive and authoritative assessment through a model intercomparison project (MIP). Given the many uncertainties related to their impacts, such an assessment of VSLS requires a multi-model approach and an international effort.

The primary objectives of this activity are to:

  • Assess the impact of industry-related emissions of chlorinated VSLSs on stratospheric ozone.
  • Assess new metrics (including integrated ozone depletion (IOD) and stratospheric ozone depletion potential (SODP)) for evaluation of the impact of VSLSs on ozone depletion.
  • Evaluate the impact of VSLSs on long-term trends (past and future) in lower stratospheric ozone.


The planned objectives/deliverables of this activity are:

  1. A set of community model simulations for (i) 1990s to present day and (ii) the future utilising common spatially-resolved industrial emissions of major VSLS. Some of the models will also use state-of-the-art iodine schemes and investigate the role of iodine through specified surface emissions of industrial iodinated VSLS.
  2. Multi-model assessment of ozone and halogen changes due to VSLS.
  3. Evaluation of metrics for VSLS impacts on ozone.
  4. Peer-reviewed publications based on multi-model assessments of (i) historical impacts, (ii) projections and future impacts, (iii) policy metrics.

The aspiration is for the assessment of historical impacts and some results on policy metrics to be completed in time for inclusion in the 2026 Ozone Assessment.

Website for further information