by Australia’s Black Summer wildfires in 2020 widened the ozone hole by 10 percent, according to a new study that warns smoke particles from such fires can erode the protective layer on earth that shields it from the sun’s ultraviolet radiation.
The research, published last week in the journal Nature, assessed the impact of smoke from the Black Summer mega wildfire in eastern Australia, which burned from December 2019 to January 2020, killing 36 people directly and harming over three billion animals.
The megafire, which is Australia’s most devastating on record, scorched tens of millions of hectares and pumped over a million tons of smoke into the atmosphere, researchers including those from the US’s Massachusetts Institute of Technology say.
Scientists identified a new chemical reaction that caused smoke particles from Australia’s wildfires to exacerbate ozone depletion.
They say the fires may have caused a 3 to 5 percent depletion of all ozone in regions across Australia, New Zealand and parts of Africa and South America by triggering this chemical reaction.
The study suggests that by the end of 2020, the fires may also have eaten at the edges of the ozone hole over Antarctica, expanding it by 2.5 million square kilometers, or about 10 percent of its area, compared to the previous year.
While the United Nations recently noted that ozone depletion around the world is on the path to recovery due to international efforts to phase out chemicals that deplete the Earth’s protective layer, scientists say the long-term impact of wildfires on their recovery remain unclear.
Previous research had found that chlorine-containing compounds, such as those emitted from factories, can react with the surface of fire aerosols and trigger a cascade of chemical reactions that produce chlorine monoxide – the ultimate ozone-depleting molecule.
The new study found that the Australian wildfires likely depleted ozone through this chemical reaction.
As long as chemicals from such mega wildfires remain in the atmosphere, researchers say they could trigger a reaction that temporarily depletes the ozone layer.
“The effects of forest fires have not been taken into account so far [projections of] ozone recovery. And I think that effect could depend on whether fires become more frequent and intense as the planet warms,” said study co-author Susan Solomon of MIT.
The researchers also found that some of the chlorine-related chemistry they detected in the atmosphere could not explain all of the changes they found in Earth’s upper atmosphere.
When scientists analyzed the composition of molecules in the stratosphere after the Australian wildfires using satellite data, they found elevated chlorine monoxide levels and a drop in hydrochloric acid concentrations.
Studies have shown that when chlorine is bound in the form of HCl, it does not destroy ozone, but when the acid molecules break apart, the chlorine can react with oxygen to form the ozone-depleting chlorine monoxide.
“The fact that HCl has dropped by this unprecedented amount at mid-latitudes was kind of a danger signal to me,” said Dr. Solomon.
“It’s kind of a race against time now. Hopefully, chlorine-containing compounds will be destroyed before the frequency of fires increases with climate change. This is all the more reason to be vigilant about global warming and these chlorine-containing compounds,” she added.
