The Montreal Protocol has been hailed for controlling chlorine-based chemicals that created a vast hole in the ozone layer over Antarctica. But new research by British and American scientists suggest a chemical not controlled by the international treaty poses a potential risk to the Earth’s protective ozone layer.

The chemical is dichloromethane – a chlorine-based industrial solvent and paint stripper whose concentrations have been rising rapidly in the atmosphere over the past decade. In a study published June 27 in Nature Communications, the scientists report that if dichloromethane concentrations continue to increase, it could offset some gains made under the Montreal Protocol and delay the recovery of the ozone layer.

“The increases observed for dichloromethane from our measurements are striking and unexpected,” said NOAA scientist Steve Montzka, a co-author on the paper. “Concentrations were decreasing slowly in the late 1990s, but reversed course and have doubled since the early 2000s.”

Unlike chlorofluorocarbons (CFCs) and similar long-lived gases that are responsible for most ozone depletion, dichloromethane has a short lifetime and is not controlled by the Montreal Protocol.

The rapid increase in dichloromethane was revealed by long-term NOAA atmospheric measurements at sites across the globe. Scientists ran computer model simulations to determine the impact of the dichloromethane increase on the ozone layer to date, and how that impact could change in the future.

“While ozone depletion from dichloromethane is currently quite modest, it is uncertain how atmospheric concentrations of this gas will change in the future,” said lead author Ryan Hossaini, of the Lancaster Environment Centre at Lancaster University. “We should be mindful to the growing threat to stratospheric ozone posed by dichloromethane and similar chemicals not controlled by the Montreal Protocol.”

Further information: University of Lancaster press release

The research paper, 'The increasing threat to stratospheric ozone from dichloromethane', was published in the journal Nature Communications on June 27, 2017.