Madrid. Researchers at the Massachusetts Institute of Technology (MIT) discovered that smoke from Australia’s Black Summer bushfires triggered stratospheric chemical reactions that helped destroy ozone.
The study, published in the journal Proceedings of the National Academy of Sciencesis the first to point to the chemical link between wildfire smoke and the destruction of ozone, which shields Earth from incoming ultraviolet radiation.
The Australian bushfires of 2019 and 2020 were historic in how far and fast they spread and how long and how powerful they burned. In all, the devastating fire burned across more than 43 million acres of land (about 17.4 million hectares) and killed or displaced nearly 3 billion animals. They also released more than a million tons of smoke particles into the atmosphere, reaching up to 35 kilometers above the Earth’s surface, a mass and range comparable to that of an erupting volcano.
less nitrogen dioxide
In March 2020, shortly after the fires subsided, the team observed a sharp drop in nitrogen dioxide in the stratosphere, which is the first step in a chemical cascade known to end in ozone depletion. The researchers found that this drop in nitrogen dioxide is directly related to the amount of smoke that the fires released into the stratosphere. They calculate that this smoke-induced chemistry depleted the column of ozone by one percent.
lost recovery
To put this in context, they point out that the phasing out of ozone-depleting gases under a global agreement to stop their production has led to the recovery of about one percent of earlier ozone declines in the past. 10 years, which means the wildfires canceled out those hard-won diplomatic gains for a short time.
If future wildfires are stronger and more frequent, as is expected with climate change, the projected ozone recovery could be delayed by years, they say. “The Australian fires look like the biggest event yet, but as the world continues to warm, there’s every reason to think these fires will become more frequent and more intense,” lead author Susan Solomon, Professor of Scientific Studies, said in a statement. Environmental at MIT. It’s another wake-up call, like the Antarctic ozone hole was, showing how bad things could be.
Massive forest fires are known to generate pyrocumulonimbus, that is, towering clouds of smoke that can reach the stratosphere, the layer of the atmosphere that is between 15 and 50 kilometers above the Earth’s surface. The smoke from Australia reached 35 kilometers in height.
In 2021, Solomon’s co-author Pengfei Yu of Jinan University, Lebanon, conducted another study on the impact of the fires and found that accumulating smoke heated parts of the stratosphere by as much as 2 degrees Celsius, a warming that persisted. for six months. The study also found evidence of ozone destruction in the southern hemisphere following the fires.
volcanic aerosols
Solomon wondered if smoke from the fires might have depleted ozone through chemistry similar to that of volcanic aerosols. Large eruptions can also reach the stratosphere, and in 1989 Solomon discovered that particles from these emissions can destroy ozone through a series of chemical reactions.
When particles form in the atmosphere, they accumulate moisture on their surface. Once wet, the particles can react with chemicals circulating in the stratosphere, including dinitrogen pentoxide, which reacts with the particles to form nitric acid.
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