A wildfire could pump smoke into the stratosphere, where particles have drifted for more than a year. A new study from the Massachusetts Institute of Technology (MIT) in the United States has discovered that as long as these particles remain suspended, they can trigger chemical reactions that corrode the brain. ozone protective layer It protects the earth from harmful ultraviolet radiation from the sun.
The research, published in the journal Nature, focuses on the smoke from the Black Summer megafire that burned in eastern Australia between December 2019 and January 2020. hectares and pumped more than a million tons of smoke into the atmosphere.
The MIT team has identified a new chemical reaction in which smoke particles from Australian bushfires worsen ozone depletion. By triggering this reaction, the fires likely contributed to a 3-5% reduction in total ozone in the mid-latitudes of the southern hemisphere.in Australia, New Zealand, and parts of Africa and South America.
The researchers’ modeling also shows that the fires affected the polar regions and eroded the edges of the ozone hole over Antarctica. At the end of 2020, Smoke particles from Australian bushfires have widened the Antarctic ozone hole. 2.5 million square kilometers10% of its surface compared to the previous year.
Threat to the recovery of the ozone layer
It is unclear what the long-term impact of wildfires will be on ozone recovery. The United Nations recently reported that the ozone hole and global ozone depletion are improving, thanks to continued international efforts to phase out ozone-depleting chemicals.
But MIT research suggests that as long as these chemicals remain in the atmosphere, large fires can trigger a reaction that temporarily depletes ozone. “The 2020 Australian fires were truly a wake-up call for the scientific community.“, says Susan Solomon, the Lee and Geraldine Martin Professor of Environmental Studies at MIT and a leading climate scientist who first identified the chemicals responsible for the Antarctic ozone hole.
“The impact of wildfires was not previously considered in ozone recovery projections. –he agrees– and I think this effect may be due to whether fires become more frequent and intense as the planet warms.
This new study, led by Solomon and MIT graduate student Peidong Wang, with collaborators from the Guangzhou Institute for Environmental and Climate Research, the National Oceanic and Atmospheric Administration, the National Center for Atmospheric Research, and Colorado State University, expands. the discovery was made In 2022, by Solomon and colleagues, they identified for the first time a chemical link between forest fires and ozone depletion.
They found that chlorine-containing compounds originally emitted by factories in the form of chlorofluorocarbons (CFCs) can react with the surface of fire aerosols. This interaction triggered a chemical cascade that produced chlorine monoxide, the most ozone-depleting molecule. Their results showed that Australian bushfires likely depleted ozone through this newly identified chemical reaction.
“But that didn’t explain all the observed changes in the stratosphere. There was a lot of chemistry involved with chlorine, and it was completely inappropriate,” Solomon said. In the new study, the team took a closer look at the composition of molecules in the stratosphere after the Australian bushfires. They examined three independent sets of satellite data and found that hydrochloric acid concentrations dropped sharply in mid-latitudes in the months after the fires, while chlorine monoxide concentrations increased.
Hydrochloric acid (HCl) interacts with smoke
Hydrochloric acid (HCl) exists as CFCs in the stratosphere. naturally degrades over time. As long as chlorine is bound in the form of HCl, it has no chance to destroy ozone. But if HCl breaks down, chlorine can react with oxygen to form chlorine monoxide, which destroys the ozone layer.
In polar regions, HCl It can break by interacting with the surface of cloud particles at freezing temperatures of about 155 Kelvin.. However, this reaction was not expected to occur in mid-latitudes, where temperatures are much higher.
So Solomon wondered if HCl could interact with smoke particles at higher temperatures and to release chlorine to destroy ozone. If such a reaction were possible, it would explain the instability of the molecules and much of the ozone destruction observed after the Australian bushfires.
The team scoured the chemical literature to see what types of organic molecules could react with HCl at higher temperatures and break it down. “I’ve found that HCl is extremely soluble in a wide variety of organic species,” he recalls. “It likes to stick to a lot of compounds.”
When the team expands its search, He found that smoke particles persisted for months, circulating in the mid-latitude stratosphere, in the same regions, and at times when HCl concentrations dropped. “It’s actually the old smoke particles that absorb most of the HCl,” says Solomon. “And then, surprisingly, you get the same reactions as in the ozone hole, but at mid-latitudes, at much higher temperatures.”
When the team modeled this new chemical reaction on a model of atmospheric chemistry and simulated Australian bushfire conditions, 5% ozone depletion in the entire stratosphere and 10% increase in ozone hole observed at mid-latitudes over Antarctica.
Reaction with HCl is probably the main way wildfires can deplete ozone.. But Solomon speculates that there may be other chlorine-containing compounds drifting in the stratosphere that could be released by wildfires.
“We’re kind of in a race with time now,” he says.
Reference work: https://www.nature.com/articles/s41586-022-05683-0
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