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Paris - Earth's protective ozone layer, on a slow path to recovery since the 1987 Montreal Protocol banned chemicals that erode it, may be in renewed danger, scientists warned on Tuesday.
Levels in the stratosphere of dichloromethane, a chemical not covered by the ozone rescue pact, are increasing rapidly and could delay the layer's recovery, they said.
Harmful ultraviolet light
Although "currently modest, the impact of dichloromethane on ozone has increased markedly in recent years," a team reported in the journal Nature Communications.
"Sustained growth in dichloromethane would... offset some of the gains achieved by the Montreal Protocol, further delaying recovery of Earth's ozone layer".
The layer sits in the stratosphere at 10 to 50km above the Earth's surface, where it filters out harmful ultraviolet light that can cause cancer and damage crops.
The Montreal accord phased out production of chlorofluorocarbons (CFCs) in refrigerators, aerosols, air-conditioners and foam insulation when it was discovered they were responsible for the so-called ozone "hole".
CFCs were replaced in the 1990s by hydrofluorocarbons (HFCs), which were safe for the now-healing ozone but also highly effective at trapping heat in the atmosphere, contributing to global warming.
Paint strippers
An amendment to the pact, to phase out HFCs, was signed in Kigali in February.
Scientists have already raised concern about the potential ozone impact of manmade chemicals called "very short-lived substances" or VSLS, such as dichloromethane.
VSLS gases usually break down in less than six months.
The new study sought to quantify the harm threatened by dichloromethane, which is used as a solvent in paint strippers and as a degreaser, and also to decaffeinate coffee.
The researchers found that dichloromethane levels in the stratosphere have nearly doubled since 2004.
Further growth could delay the ozone recovery over Antarctica, where the depletion was most severe, by more than a decade.
And the authors noted that other VSLS have also been detected in the atmosphere, but have yet to be measured.
Policy work
Experts not involved in the study welcomed its contribution to understanding what is happening to the ozone layer.
"We must act now to stop its (dichloromethane's) release to the atmosphere in order to prevent undoing over 30 years of exemplary science and policy work which has undoubtedly saved many lives," said Grant Allen, an atmospheric physicist at the University of Manchester.
