Chemicals used to decaffeinate coffee, produce paint removers, meld plastics and purify antibiotics are contributing to the depletion of the ozone layer over the tropics.
Since the Montreal protocol in 1987, when countries agreed to phase out the use of chlorofluorocarbons (CFCs) and other harmful aerosols, the ozone layer has been healing. But one part of it, in the tropical lower stratosphere, has shown signs of depletion in recent years.
Researchers have blamed climate change for this discrepancy, as a warmer atmosphere accelerates the flow of warm air from the tropics to the poles, thinning the ozone layer in the tropics.
But research from Julián Villamayor at the Institute of Physical Chemistry in Madrid, Spain, and his colleagues suggests pollution from short-lived chemicals is also to blame.
Very short-lived substances (VSLS) are ozone-depleting chemicals that typically last for just six months in the atmosphere. Some, such as bromine, are naturally occurring, while others, such as dichloromethane, are industrially produced. They are used for a whole range of applications, including extracting caffeine from coffee and as an aerosol spray propellant. Despite being known to attack the ozone layer, their use isn’t regulated by the Montreal protocol.
These substances are harming the ozone layer in the tropical lower stratosphere, says Villamayor. “They are so short-lived that they don’t reach higher levels of the stratosphere, nor the polar regions,” he says. “But they get to penetrate the stratosphere via the very strong tropical convection and they get to react in the lowermost layer of the stratosphere.”
Villamayor and his colleagues used sophisticated climate models to simulate the impact of emissions from all naturally occurring and human-made VSLS on the ozone layer, and found they may account for up to a quarter of the damage to the layer in the tropics over the past 20 years. Climate change is responsible for the rest.
In the future, uncontrolled use of human-made VSLS could increase ozone depletion in the tropical stratosphere by 30 per cent by the end of the century, says Villamayor.
This could have serious implications for the millions of people living in the tropical belt, one of the world’s most populous areas, leading to increased rates of skin cancer, reduced crop yields and disruptions in the marine food chain.
Villamayor says countries should consider amending the Montreal protocol to restrict the use of VSLS.
Neil Harris at Cranfield University, UK, says the research is robust and agrees that VSLS use should face tighter controls. “There should be a drive for reducing the emissions of these compounds, without doubt,” he says.
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