Ozone progress threatened – Experts respond

Ozone thumb
Credit: University of Leeds

Scientists report that chemicals that are not controlled by a United Nations treaty designed to protect the Ozone Layer are contributing to ozone depletion.

In the new study, published in Nature Geoscience, UK scientists also report that the atmospheric abundance of one of these ‘very short-lived substances’ (VSLSs), dichloromethane,  is growing rapidly.

VSLSs, which includes gases from natural and industrial sources, are not covered by the Montreal Protocol, a ban on ozone depleting compounds.

“We have identified now that one of these chemicals is increasing rapidly and, if this increase is allowed to continue, it could offset some of the benefits to the Ozone Layer provided by the Montreal Protocol,” say the authors.

The SMC collected the following expert commentary. Feel free to use these quotes in your reporting. If you would like to contact a New Zealand expert, please contact the SMC (04 499 5476; smc@sciencemediacentre.co.nz).   

Dr Joseph Lane, Senior Lecturer in Physical and Theoretical Chemistry, University of Waikato, comments:

“The Montreal Protocol has undoubtedly had a significant positive impact on the ozone layer and its global adoption should be celebrated. However like so many other policy or legislation documents, it suffers from the cat and mouse game of specifying prohibited behaviour rather than specifying allowed behaviour. It’s a little like the debacle that we used to suffer from in New Zealand with legal highs. Importers/distributors were previously allowed to sell a given drug until it was shown to be harmful rather than being first required to prove that it was safe. As soon as a particular drug was banned, a slight variant was sold instead.

“The same thing has been happening with ozone depleting substances. When the Montreal Protocol was first established it just restricted the use of CFCs (chlorofluorocarbons) and industry responded by using slight variants known as HCFCs (hydrochlorofluorocarbons). The Montreal Protocol was later amended to restrict usage of HCFCs and again industry responded by increasing use of another slight variant known as VSLS (very short lived substances). The present research by Hossaini and co-workers now shows that these VSLS are also having a damaging effect on the ozone layer.”

Dr Karin Kreher, Senior Scientist and Director of Bodeker Scientific, comments:

“The study by Hossaini et al. shows that it is not just chlorofluorocarbons (CFCs) and halons that deplete the stratospheric ozone layer. In addition to these emissions, which are controlled by the Montreal Protocol, emissions of other substances containing chlorine and bromine are also important for the ozone layer with emissions of these so-called very short-lived substances (VSLSs) being uncontrolled. Bromine, predominantly released into the stratosphere following the degradation of naturally emitted VSLSs is responsible for ~85% of the ozone destruction in the altitude range where changes in ozone have a strong impact on surface climate.

“Their study shows that although the Montreal Protocol has clearly been successful in protecting the ozone layer, we cannot let our guard down. Ongoing vigilance is required for uncontrolled emissions of other substances that might have a greater impact on the ozone layer than expected to date.

“Although short-lived brominated substances are emitted naturally by seaweed and phytoplankton, we need to keep in mind that should emissions of these substances increase, they could have a noticeable impact on ozone and hence on climate. Increases in emissions could result from climate change-driven increases in their fluxes from the ocean and from an increase in industrial seaweed cultivation.

“Hossaini and colleagues also state that the absolute contribution of VSLSs to stratospheric bromine is uncertain due to our limited knowledge of the magnitude and distribution of their emissions. Measurements of emissions of bromoform and dibromomethane globally, and along the New Zealand coast in particular, would advance our understanding of the processes that control emissions and how these processes may respond to changes in the environment. A more quantitative understanding of the halocarbon emission process is an essential prerequisite for high-confidence model projections of future changes in the ozone layer and its effect on climate. ”

Dr Olaf Morgenstern, Atmospheric Scientist, NIWA, comments:

Could these VSLS undo the progress made by the Montreal Protocol?

“No, not completely. The Montreal Protocol has led to the phase-out of the most damaging class of ozone-depleting substances. The “very short-lived species” are mostly natural (particularly the brominated ones) and to a minor extent industrially produced. Crucially, their lifetimes are relatively short and efficiency of transport into the stratosphere relatively small, compared to long-lived ozone-depleting substances. It would take a pretty drastic increase for them to really undo the success of the Montreal Protocol. Also dichloro-methane is partly a by-product of the production of a temporary replacement compound (replacing the chlorofluorocarbons) which is due to be phased out over the coming decades. If CH2Cl2 was considered to be a threat, the Montreal Protocol would like be amended to bring down its production.”

What are the sources of these VSLS?

“For the brominated substances, mostly oceanic natural production by seaweeds and phytoplankton. The seaweed-related part is partly subject to aquaculture and might increase. Chlorinated compounds, particularly dibchloromethane, are man-made and used in industrial processes. In terms of their ozone-depletion potential, brominated species are substantially more important than the chlorinated compounds.”

Should they be controlled in a manner similar to the Montreal Protocol?

“There is no point in controlling natural gases. The industrially produced compounds should maybe be included in the Protocol if they indeed constitute a major remaining source of stratospheric chlorine. The Protocol has repeatedly been amended in the past to reflect new insights in this area.”

Would areas in higher latitudes, such as NZ and Antarctica, be disproportionally affected by VSLS ozone impacts?

“Injections of halogens into the stratosphere always affect Antarctica most, due to the Antarctic meteorology. This is the reason for the Antarctic ozone hole. But the projection is still for chlorine and bromine to continue to decline in the stratosphere. Climate change is of course of general concern, but the contribution of any increase in these “very short-lived substances” to Southern-Hemisphere climate change to date is thought to be small and unidentifiable at present.”