A new study has found that high clouds of smoke sent into the stratosphere from raging wildfires can destroy Earth’s ozone layer due to a potent mix of smoke, atmospheric chemicals and ultraviolet light.
During late 2019 and early 2020, Australia’s skies darkened, darkened by thick columns of smoke from wildfires that reached into the stratosphere. Subsequently, satellite data showed that the smoke was somehow reacting with atmospheric molecules to eat up the earth’s ozone layer ,Sn: 3/17/22, But exactly how this was happening was not clear.
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Now, scientists have put together pieces of the chemical puzzle, Once in the stratosphere, the team says, the smoke particles were able to interact with stratospheric gases as well as emit ozone-destroying chemicals. Add in solar radiation, and that smog brews churned out chlorine radicals, a type of chemical known to attack ozone, researchers reported in March 9. Nature,
Researchers estimate that this series of events was responsible for about 3 to 5 percent of the depletion of the ozone layer over parts of the Southern Hemisphere during 2020. That’s a tiny fraction of the whole — but it rivals the scale of the impact of human emissions of ozone-eating chlorofluorocarbons, says MIT atmospheric chemist Susan Solomon.
Chlorofluorocarbons were once used in air conditioners and refrigerators, but their emissions into the atmosphere caused a large hole in Earth’s protective ozone layer over Antarctica, which would have limited the amount of ultraviolet radiation from the Sun reaching the planet’s surface. Is.
In the new study, Solomon and colleagues compared atmospheric observations of chlorine, ozone and other molecules following Australian wildfires with simulations of atmospheric chemistry. Satellites measured the abundance of certain chemicals in the stratosphere in 2020 – not just ozone, but also hydrogen chloride gas and chlorine nitrate. Those levels caught Solomon’s attention.
“What we saw in Australia was a tremendous drop in hydrogen chloride,” says Solomon. “I thought, God, this looks like Antarctica. How could this be on Australia?”
Hydrogen chloride gas is a product of the breakdown of chlorofluorocarbons, which can persist in the stratosphere for decades. The cold atmosphere above Antarctica was an important part of the formation of the ozone hole, because at that temperature hydrogen chloride gas can condense into icy clouds traveling through the stratosphere. The absorption of that gas is necessary to start the chain of reactions that create ozone-depleting chemicals.
Australia’s atmosphere is too hot for this process – but satellite data indicated that something was still ejecting hydrogen chloride gas from the atmosphere. Solomon and his team realized that the culprits were organic particles in the smoke. Those particles can also absorb hydrogen chloride gas at warmer temperatures, which is a necessary first step.
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Along with the absorbed hydrogen chloride, the smoke particles can act as catalysts, helping to speed up other reactions in the atmosphere. In particular, the particles accelerate the transformation of other chlorine-containing gases floating in the stratosphere, such as chlorine nitrate and hypochlorous acid, into chlorine compounds, which are highly reactive to sunlight.
Mixing the sun’s ultraviolet radiation with those new chlorine compounds produces chlorine radicals, freewheeling molecules that are chemically highly reactive—and particularly enjoy attacking ozone molecules.
Solomon says the discovery of this wildfire-related process for destroying ozone is a worrying potential blow to ozone layer recovery. The 1987 Montreal Protocol targeted the use of chlorofluorocarbons, which were phased out by 2010, an act that has been overwhelmingly successful Shrinking the hole in the ozone over Antarctica (Sn: 2/10/21, She says the ozone layer has since shown signs of recovery, growing back on the order of 1 percent per decade.
However, the smoke from the Australian wildfires has more or less “erased all that hard work” of the year, Solomon says.
Climate change is expected to increase the intensity and frequency of wildfires around the world giant fire cloud in the high sky (Sn: 12/15/20, If these fires are a “one-time deal, it’s not so bad” for ozone recovery, says Solomon. “But if it happens every five years, that’s a different kettle of fish.”
The study explains several intriguing satellite observations made in the wake of the Australia fires, says Ross Salawich, an atmospheric chemist at the University of Maryland in College Park, who was not involved in the work. This explains the decline in hydrogen chloride, he says, as well as the strange increase in other chlorine compounds such as chlorine nitrate and chlorine oxide.
But the “icing on the cake”, Salavitch says, is how discovering the role of organic particles could improve our understanding of what controls the size of the ozone hole. This is important, not only because we want to get the details right, he says, but because “one of the unfortunate consequences of global warming is likely an increase in the frequency and severity of wildfires.”