A wildfire that swept through southeast Australia in 2019-20 unleashed chemicals that widened the ozone layer, according to a new study published in Nature. The study warned that smoke particles from such fires can erode the Earth’s protective layer that shields the planet from the Sun’s ultraviolet radiation. The wildfire raged from December 2019 to January 2020, killing 36 people and injuring more than three billion people. It was spread across millions of acres and released over a million tons of smoke into the atmosphere.
The smoke triggered by Australia’s most devastating fire on record went to heights of upto 30 kilometres, said the study published last week. This is the area of the stratosphere that contains the ozone layer, according to the study’s co-author Kane Stone, an atmospheric chemist at the Massachusetts Institute of Technology (MIT) in Cambridge.
The researchers involved in the study also identified a new chemical reaction by which smoke particles made the ozone depletion worse.
The impact was so severe that three to five per cent of the ozone layer was deleted in regions overlying Australia, New Zealand, and parts of Africa and South America.
The study is based on the analysis of satellite data that revealed that the levels of hydrochloric acid were especially low compared to other years in regions of the atmosphere away from the South Pole.
This is the remnant chlorine left behind by chloroflourocarbons that is harmless to the ozone layer. But when hydrochloric acid dissolves in water droplets, it forms reactive ozone-depleting molecules.
This phenomenon is generally not visible around the poles, because the air is too warm. But the satellite data showed how various organic acids contained in smoke particles altered the solubility of hydrochloric acid after the fires.
Another co-author of the study, Susan Solomon, said the hydrochloric acid, together with smoke particles, produced molecular chlorine, which broke down into highly reactive ‘ozone-eating’ chlorine atoms.
“Wildfire smoke at warm temperatures does things over Australia that couldn’t otherwise happen,” Solomon is quoted as saying in the study.
“There’s now sort of a race against time. Hopefully, chlorine-containing compounds will have been 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.
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