The destruction wrought by wildfires was similar to the formation of the ozone hole in Antarctica each spring, “but with much warmer temperatures”, according to the principal investigator of one study.
Particles in wildfire smoke can activate molecules that deplete the ozone layer, according to new research that suggests future ozone recovery could be delayed by increasingly intense and frequent fires.
A study published in the journal Nature found that smoke from the 2019-20 Australian bushfires temporarily destroyed the ozone layer by 3-5% in 2020.
The smoke from the fires circulated across the globe was ejected into the stratosphere, the second layer of Earth’s atmosphere, by a pyrocumulonimbus cloud.
In the ozone layer, part of the stratosphere, ozone gas molecules absorb high-energy ultraviolet rays from the sun. This decreases the amount of radiation reaching the Earth’s surface.
Ozone depletion by smoke particles
The lead researcher, Professor Susan Solomon, an atmospheric scientist at the Massachusetts Institute of Technology in the US, said that the destruction of ozone by smoke particles was similar to the process of formation of the hole in the ozone layer in Antarctica each spring, “but at much warmer temperatures“.
Smoke aerosols, the researchers found, can activate chlorine to form compounds that destroy ozone molecules.
Solomon said chlorine in the stratosphere has declined since the 1987 Montreal Protocol eliminated the use of ozone-depleting chlorofluorocarbons. “There is a tremendous science policy success story there.“, he said. “Slow recovery of the ozone layer is on the order of 1% per decade at mid-latitudes”.
But he warned that more frequent fires could delay ozone recovery. “suddenly in a year , we had a loss of 3% to 5%. It will bounce back if it’s the only year this happens, but not if it keeps happening.“.
Forest fires delay recovery of the ozone layer
“The question on my mind is, will man-made chlorine be diluted and destroyed from the atmosphere faster than global climate change will increase the frequency and intensity of these types of fires? I think it will be a race”.
The Doctor. Martin Jucker, a professor at the University of New South Wales who was not involved in the research, agrees that the hole in the ozone layer could heal more slowly than expected as a result of more wildfires in the future.
“Of particular concern for Australia is the extent of the ozone hole towards the equator, meaning the ozone layer could become thinner much closer to where millions of Australians live.“, he said.
Laura Revell, an atmospheric scientist at the University of Canterbury in New Zealand, said: “The first signs of ozone recovery in Antarctica are visible since the mid-2010s. No major changeswe expect stratospheric chlorine concentrations to gradually decline this century and the hole in the ozone layer to shrink year by year.
“Of concern is that while the hole in the ozone layer normally forms over Antarctica due to low temperatures, aerosols from wildfires appear to be able to promote ozone losses in the relatively warmer temperatures present at mid-latitudes which are densely populated.”.
Solomon and his colleagues identified that the ozone depletion process was triggered by the dissolution of hydrochloric acid in the stratosphere in smoke aerosols.
Hydrochloric acid dissolved about a thousand times more easily in smoke aerosols than in “the normal stratospheric particles of sulfuric acid and waterSolomon said.
“From a scientific point of view, it is very exciting to see this new effect“, he said. “From a planetary point of view… it would simply be tragic if humanity were to screw up the ozone hole solution by deciding that we are going to [permitir] many more of these fires if we don’t mitigate climate change”.
Solomon added that it was important to determine whether smoke from fires in Australia, where native forests are dominated by eucalyptus, differs in composition from fires in other areas. “I don’t really see a chemical reason for this, but it should be investigated.”.