Researchers have discovered that chemicals historically not linked to ozone damage are now growing to threatening levels, negating any recovery the layer has achieved.
Called "very short-lived substances," the chemicals are produced both naturally and synthetically, but industrial use of VSLS is not sanctioned under the United Nations Montreal Protocol since the chemicals only contribute little to depleting the ozone layer.
One particular kind of VSLS, however, has been growing in level, which when allowed to persist could negate some of the good achieved through the Montreal Protocol.
Researchers created a 3D render of the atmosphere, factoring in damage caused by VSLS on the ozone and the climate. VSLS measurements over the last 20 years were also analyzed and it was from this analysis that researchers found that a man-made chemical called dichloromethane has been rapidly increasing in concentrations in the atmosphere.
"At present, the long-term recovery of the Ozone Layer from the effects of CFCs is still on track, but the presence of increasing dichloromethane will lead to uncertainty in our future predictions of ozone and climate," warned Martin Chipperfield, a School of Earth and Environment professor from the University of Leeds and one of the co-authors for the study.
VSLS are a concern because -- while they contribute to a lesser extent to ozone depletion compared to the damage longer-lived gases such as chlorofluorocarbons are responsible for -- they are nearly four times more effective at affecting climate. This is because VSLS destroy the lowest portion of the stratosphere when they break down. Just losing a molecule of ozone from this region has a bigger impact on the climate compared to destroying a molecule from higher portions by a longer-living gas.
VSLS from natural sources such as seaweed in the ocean currently account for about 90 percent of all VSLS-related ozone loss in the lower stratosphere. VSLS from industrial sources, however, have been increasing over the last few years and will continue to increase in the future.
Dr. Ryan Hossaini, also from Leeds' School of Earth and Environment and lead author of the study, said that it is uncertain what is fueling the growth of dichloromethane but it may be partly due to industrial processes that require the use of hydrofluorocarbons. As HFCs are supposedly kinder to the ozone layer, it's ironic then that they would be the source of ozone-depleting gases in the atmosphere.
The study, published in the journal Nature Geoscience, received funding support from the Natural Environment Research Council.
