The researchers also reported that the atmospheric abundance of one VSLS is growing rapidly. Their paper is published in the journal Nature Geoscience.

VSLS can have both natural and industrial sources. Industrial production of VSLS is not controlled by the United Nations Montreal Protocol because historically these chemicals have contributed little to ozone depletion. But we have identified now that one of these chemicals is increasing rapidly and, if this increase is allowed to continue, it could offset some of the benefits to the Ozone Layer provided by the Montreal Protocol.

—Dr. Ryan Hossaini, lead author

Short-lived bromine substances are produced naturally by seaweed and phytoplankton, whereas short-lived chlorine substances are primarily anthropogenic, the authors noted. Measurements of VSLS in the atmosphere over the past two decades, provided by collaborators from the National Oceanic and Atmospheric Administration (NOAA), revealed a rapid increase in atmospheric concentrations of dichloromethane, a man-made VSLS used in a range of industrial processes.

At present, naturally-emitted VSLS account for around 90% of the total ozone loss caused by VSLS in the lower stratosphere. However, the contribution from man-made VSLS compounds is increasing and appears set to increase further in coming years.

In the study, the researchers used a 3D computer model of the atmosphere to determine the impact of VSLS on ozone and climate. They found that ozone loss from very short-lived substances (VSLS) had a radiative effect nearly half that from long-lived halocarbons in 2011 and, since pre-industrial times, has contributed a total of about −0.02 W m⁻² to global radiative forcing.

Dr. Hossaini said that because VSLS have short atmospheric lifetimes, they break down and destroy ozone in the lowermost part of the stratosphere. This is important, as a molecule of ozone lost in this region has a far larger impact on climate than a molecule destroyed at higher altitudes by longer-lived gases.

We need to continue monitoring the atmospheric abundance of these gases and determine their sources. 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.

—Professor Martyn Chipperfield, co-author

Study co-author Dr, Stephen Montzka from NOAA observed that the increases observed for dichloromethane were unexpected; concentrations had been decreasing slowly in the late 1990s, but since then have increased by about a factor of two at sites throughout the globe.

It is uncertain what is driving this growth. However, it could be partly due to the fact that dichloromethane is used in the manufacturing process of some HFCs, the 'ozone-friendly' gases which were developed to replace CFCs. This would mean, ironically, that production of ozone-friendly chemicals is actually releasing some ozone-destroying gases into the atmosphere.

—Dr. Hossaini

Resources

• R. Hossaini, M. P. Chipperfield, S. A. Montzka, A. Rap, S. Dhomse & W. Feng (2015) “Efficiency of short-lived halogens at influencing climate through depletion of stratospheric ozone” Nature Geoscience doi: 10.1038/ngeo2363