According to a new study, smoke particles in the stratosphere can cause chemical reactions that deplete the ozone layer, and smoke particles from Australian wildfires widened the ozone hole by 10% in 2020.
Smoke from a wildfire can linger in the stratosphere for up to a year.
Smoke particles from wildfires can erode the ozone layer
The study, which will be published in Nature, focuses on the smoke from the "Black Summer" mega-fire that burned in eastern Australia from December 2019 to January 2020, as per ScienceDaily.
The fires scorched tens of millions of acres and released over a million tons of smoke into the atmosphere, making them the most dangerous on record in the country.
The MIT team discovered a new chemical reaction by which smoke particles from Australian wildfires exacerbated ozone depletion.
The fires likely contributed to a 3-5 percent depletion of total ozone at mid-latitudes in the southern hemisphere, overlying Australia, New Zealand, and parts of Africa and South America by triggering this reaction.
The fires, according to the researchers' model, had an effect in the polar regions as well, eating away at the edges of the ozone hole over Antarctica.
Smoke particles from Australian wildfires had expanded the Antarctic ozone hole by 2.5 million square kilometers, or 10% of its original size, by late 2020.
It's unclear what effect wildfires will have on ozone recovery in the long run.
The United Nations recently reported that the ozone hole and global ozone depletion are on the mend, thanks to a concerted international effort to phase out ozone-depleting chemicals.
However, according to the MIT study, as long as these chemicals remain in the atmosphere, large fires could cause a reaction that temporarily depletes ozone.
The team examined the composition of molecules in the stratosphere following the Australian wildfires in the new study.
They examined three separate sets of satellite data and discovered that in the months following the fires, concentrations of hydrochloric acid dropped significantly at mid-latitudes, while chlorine monoxide increased.
As CFCs degrade naturally, hydrochloric acid (HCl) is present in the stratosphere. As long as chlorine is bound in the form of HCl, it cannot destroy ozone.
However, if HCl disintegrates, chlorine can react with oxygen to produce ozone-depleting chlorine monoxide.
Also Read: Each Year, Smoke Particles From Human-lit Fires Cause More Than 80% Of All Smoke-related Deaths
The smokey drift
Solomon and her colleagues combed the chemical literature for organic molecules that could react with HCl at higher temperatures to break it down, as per MIT News.
"I discovered that HCl is extremely soluble in a wide range of organic species," Solomon says. "It likes to cling to a variety of compounds."
The question then became whether the Australian wildfires released any of the compounds that could have caused HCl breakup and subsequent ozone depletion.
When the team examined the composition of smoke particles in the days following the fires, the picture was far from clear.
When the researchers broadened their search, they discovered that smoke particles persisted for months, circulating in the stratosphere at mid-latitudes, in the same regions and times when HCl concentrations dropped.
When the researchers incorporated this new chemical reaction into an atmospheric chemistry model and simulated the conditions of the Australian wildfires, they discovered a 5% depletion of ozone in the stratosphere at mid-latitudes, as well as a 10% widening of the ozone hole over Antarctica.
The reaction with HCl is most likely the primary mechanism by which wildfires deplete ozone.
However, Solomon believes that there may be other chlorine-containing compounds floating in the stratosphere that wildfires could ignite.
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