Rising global emissions of some chlorine-containing chemicals could slow the progress made in healing the ozone layer. A study found the substances, widely used for paint stripping and in the manufacture of PVC, are increasing much faster than previously thought. Mainly produced in China, these compounds are not currently regulated.
Experts say their continued use could set back the closing of the ozone hole by up to 30 years. Scientists reported last year that they had detected the first evidence that the thinning of the protective ozone layer was diminishing.
The new paper has been published in the journal Atmospheric Chemistry and Physics.
The Montreal Protocol, which was signed 30 years ago, was the key to this progress. It has progressively helped governments phase out the chlorofluorocarbons and the hydrochlorofluorocarbons that were causing the problem. However, concern has been growing over the past few years about a number of chemicals, dubbed very short-lived substances.
Dichloromethane is one of these chemicals, and is used as an industrial solvent and a paint remover. Levels in the atmosphere have increased by 60% over the past decade.
Another compound highlighted in this new report is dichloroethane. It's used in the manufacture of polyvinyl chloride or PVC, a light plastic widely used in construction, agriculture and elsewhere.
For a long time, scientists believed that both these compounds would decay before getting up as far as the ozone layer. However, air samples analyzed in this new study suggest this view may be mistaken and these destructive elements are getting there quicker and doing more damage than thought.
The authors found that cold wind blows these chemicals from factories in China to the eastern Pacific. This is one of the main locations where air gets uplifted into the stratosphere.
Our aircraft samples show the path from emissions in China, through the tropics in Malaysia and up to about 12km in the atmosphere, said lead author Dr David Oram from the University of East Anglia.
This implies a route whereby these short-lived compounds can get into the atmosphere much quicker than if they had been released in North America or Manchester.