More dichloromethane will bring uncertainty to our future prediction of ozone and climate

Scientists report that chemicals not controlled by the United Nations treaties designed to protect the ozone layer are causing ozone depletion.

In a new study published in Nature Geoscience today, scientists also reported that the content of this "very short-lived substance" (VSLS) in the atmosphere is increasing rapidly.

Dr. Ryan Husseini from the School of Earth and Environment of Leeds University, the main author of the study, said: "VSLS can be either natural or industrial. The Montreal Protocol does not control the industrial production of VSLS, because these chemicals have made little contribution to the loss of ozone in history.

"But we have now determined that one of the chemicals is increasing rapidly. If this increase continues, it may offset some of the benefits of the Montreal Protocol to the ozone layer."

In this study, the researchers used a 3D computer model of the atmosphere to determine the impact of VSLS on ozone and climate.

The measurement results of VSLS in the atmosphere over the past 20 years provided by the collaborators of the National Oceanic and Atmospheric Administration (NOAA) are also analyzed. These measurements show that the concentration of dichloromethane in the atmosphere is increasing rapidly, and dichloromethane is an artificial VSLS used in a series of industrial processes.

Professor Martyn Chipperfield, co-author of the study and from the School of Earth and Environment of Leeds University, said: "We need to continue to monitor the content of these gases in the atmosphere and determine their sources. At present, the long-term work of recovering the ozone layer from the impact of chlorofluorocarbons is still in progress, but the presence of more and more dichloromethane will bring uncertainty to our future prediction of ozone and climate."

The researchers found that, compared with long-lived gases such as chlorofluorocarbons, the ozone loss caused by VSLS in the atmosphere is smaller at present, but the impact of ozone loss driven by vssls on the climate is almost four times that of the latter.

Dr Hossaini explained: "Because VSLS has a very short life in the atmosphere, it will destroy the ozone at the bottom of the stratosphere. This is very important, because the impact of an ozone molecule lost in this area on the climate is far greater than that of a molecule destroyed by gases with a longer life at higher altitudes."

The researchers also separated the natural source of VSLS (such as seaweed in the ocean) and VSLS released by human activities (such as industrial processes) to determine their relative importance.

At present, VSLS discharged naturally accounts for about 90% of the total ozone loss caused by VSLS in the lower stratosphere. However, the contribution of synthetic VSLS compounds is increasing and appears to be increasing further in the coming years.

The co-author of the study, Dr. Stephen Munzka of the National Oceanic and Atmospheric Administration of the United States, added: "The observed increase of dichloromethane is amazing and unexpected; in the late 1990s, the concentration has been slowly declining, but since then, the concentration in some places around the world has increased by about twice."

Dr. Hosseini said: "It is not clear what is driving this growth. However, part of the reason may be that dichloromethane is used in the manufacturing process of some hydrofluorocarbons, which are" ozone friendly "gases and have been developed to replace chlorofluorocarbons. Ironically, this would mean that the production of ozone friendly chemicals is actually releasing some ozone depleting gases into the atmosphere. "

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