The massive wildfires that raged in southeastern Australia in 2019-2020 unleashed chemicals that chewed through the ozone layer, widening and lengthening the ozone hole. Natureexplains how smoke combines with chlorine-containing molecules (remnants of now-banned chemicals) in the stratosphere to cause destruction.
The Australian fire produced the largest smoke column on record, ejecting nearly a million tons of smoke up to 30 kilometers high. It reaches into the stratosphere, the part of the atmosphere that contains the ozone layer that protects the planet from harmful ultraviolet rays, said Kane, an atmospheric chemist at the Massachusetts Institute of Technology (MIT) in Cambridge and study co-author. Stone said.
In the months following the wildfires, the annual hole in the ozone layer over Antarctica was larger and lasted longer. But Stone says researchers didn’t know why.
modified chemistry
Paper co-author Susan Solomon, also an MIT atmospheric chemist, suggests that the smoke may have triggered a chemical reaction. Satellite data after the fire revealed that hydrochloric acid levels were particularly low in the atmosphere at warmer latitudes away from Antarctica compared to other years. The stratosphere “looked like another planet after the fire,” she says.
About 80% of atmospheric chlorine is a legacy of chlorofluorocarbons, chemicals that have been used in aerosol sprays and as refrigerants since the 1930s. Their use has mostly been phased out since international conventions came into force in 1987. Residual chlorine binds to the ozone layer as harmless hydrochloric acid and chlorine nitrate.
However, when hydrochloric acid dissolves in water droplets, it forms reactive ozone-depleting molecules. That’s usually not the case because the air is too warm far from the poles, Stone said.
The team used a computer model to predict how different organic acids in smoke particles would change the solubility of hydrochloric acid. The changes generated in the simulation reflect changes in stratospheric chemistry observed after the fire.
Solomon says that hydrochloric acid attaches to the surface of smoke particles and reacts with other molecules to produce chlorine molecules, which split in sunlight into highly reactive “ozone-eating” chlorine ions. It is said that it will be.
“Wildfire smoke in warmer temperatures does things to Australia that otherwise could not have happened,” says Solomon.
Jim Heywood, an atmospheric scientist at the University of Exeter in the UK, says that post-fire hydrochloric acid solubility has not been investigated before. “It’s like the big missing piece of the puzzle,” he says.
Ozone recovery at risk
The remaining chlorine-containing molecules from before the ban are slowly decaying, shrinking the ozone hole each year. He said his recovery could be in jeopardy.
“It’s like racing,” she says. “In the next 40 to 50 years, will chlorine decay from the stratosphere fast enough that an increase in violent and frequent wildfires will not perpetuate the ozone hole?”
Not all wildfire smoke reaches the stratosphere, says David Peterson, a meteorologist at the U.S. Naval Research Laboratory in Monterey, California. But when intense fires combine with moist air overhead, fire-induced thunderstorms form chimney-like clouds that send smoke high into the atmosphere. Understanding what causes tall storm clouds to blow smoke into the stratosphere will be key to understanding the extent to which fires affect ozone recovery, he says.
Heywood hopes to integrate the new chemistry into climate models to predict how ozone depletion will be affected if intense wildfires become more common.
This article is reproduced with permission and was first published on March 8, 2023.
