Reducing dichloromethane emissions could slow ozone depletion in the tropics

As Nature Climate Change reports, climatologists at the Rocasolano Institute of Physical Chemistry modeled the effects of short-lived halogen-containing substances on tropical ozone depletion. The study found that anthropogenic and natural emissions of these substances were responsible for 25% of all tropical ozone depletion over the past 20 years.

40 years ago, scientists discovered a hole in the ozone layer over Antarctica that was caused by anthropogenic emissions of halogen-containing organic substances into the atmosphere. This led to the Vienna Convention for the Protection of the Ozone Layer, and in 1987 the Montreal Protocol was prepared for signing, listing the specific substances whose emissions were to be reduced. Most of the substances on the list were simple fluorinated and chlorinated hydrocarbons.

However, these substances are very persistent and their lifetime in the atmosphere ranges from tens to hundreds of years. When they reach the stratosphere, they release free halogens, which destroy the ozone layer. Thanks to the Montreal Protocol, the ozone layer over Antarctica has been preserved and is gradually being restored. However, the ozone concentration in the lower stratosphere of tropical latitudes is still gradually decreasing.

Until now, scientists have attributed this to changes in air mass circulation caused by greenhouse gas emissions. However, climatologists led by Alfonso Saiz-Lopez found that about a quarter of the decrease in ozone concentration is caused by short-lived halogen-containing substances, some of which enter the atmosphere due to chemical industries. One of these substances is dichloromethane, a very popular organic solvent used, for example, to extract caffeine in the manufacture of decaffeinated coffee.

Studies have shown that over the next few years, anthropogenic emissions of chlorine-containing substances will play an increasing role in the destruction of the ozone layer. By the end of the 21st century, they will be responsible for 30% of all lost ozone concentrations. Therefore, the authors of the article conclude that human activities resulting in emissions of short-lived organic substances need to be controlled.

Although the ozone layer over the tropics will still continue to shrink due to greenhouse gas emissions, control measures will significantly slow the process. Reducing dichloromethane emissions could slow the depletion of the ozone layer in the tropics and help preserve the planet’s ecological balance.

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