New threat to the ozone layer

The ozone layer protects life on Earth by absorbing much harmful ultraviolet radiation from the Sun. The 1987 Montreal Protocol got countries around the world to refuse to continue using chlorofluorocarbons, or CFCs, a class of chemicals that destroy ozone in the stratosphere and thus allow more ultraviolet radiation to reach the Earth’s surface. Fortunately, the protocol was complied with and the gradual withdrawal of CFCs was done in time to avoid greater evils.

Now, however, chemists have discovered another threat to the ozone layer, this time much more difficult to suppress than CFCs: forest fires.

A forest fire can pump smoke into the stratosphere, where the particles drift for more than a year. Susan Solomon’s team, from the Massachusetts Institute of Technology (MIT) in the United States, has discovered that, while suspended there, these particles can trigger chemical reactions that erode the ozone layer.

The study focused on a specific case, that of the smoke from the huge wave of forest fires known as “Black Summer” that broke out in eastern Australia. Those fires occurred from December 2019 to January 2020. The fire (the most devastating recorded in the country since continuous historical records have been kept) burned tens of millions of hectares and pumped more than 1 million tons of smoke into the atmosphere. .

Specifically, the MIT team identified a new chemical reaction whereby smoke particles from Australian bushfires worsened ozone depletion. By triggering this reaction, the fires likely contributed to 3 to 5 percent reductions in total ozone in the mid-latitudes of the southern hemisphere, in regions above Australia, New Zealand, and parts of Africa and South America.

The digital model with which the study authors have worked also indicates that the fires affected the polar regions, eroding the edges of the hole in the ozone layer over Antarctica. At the end of 2020, smoke particles from the Australian bushfires widened that hole by 2.5 million square kilometers, 10% of its area compared to the previous year.

This map shows the size and shape of the hole in the ozone layer above the South Pole on October 5, 2022. (Image: NASA Earth Observatory / Joshua Stevens. Modified by MIT News.)

The study is titled “Chlorine activation and enhanced ozone depletion induced by wildfire aerosol”. And it has been published in the academic journal Nature. (Fountain: NCYT by Amazings)