The ozone layer seemed to be recovering after international agreements determined that CFC gases were the cause of the hole that destroyed this layer of the atmosphere. However, it was discovered that another factor could undermine the success so far: massive forest fires. It has been confirmed for the first time that they destroy this protective shield against the sun’s rays.
Australian bushfires in 2019 and 2020 were historic in terms of how far and fast they spread and how long they lasted. In total, the devastating ‘Black Summer’ fires have razed more than 18 million hectares of land and extinguished or displaced nearly 3 billion animals. fires too they injected over a million tons of smoke particles into the atmosphere and reached a height of 35 kilometers, the mass and range comparable to that of an erupting volcano.
Now, atmospheric chemists from the Massachusetts Institute of Technology (MIT) in the USA have discovered that the smoke from these fires triggers chemical reactions in the stratosphere that contribute to the destruction of the ozone layer that protects the Earth from ultraviolet radiation. sun.
The study is the first to establish a chemical link between smoke from forest fires and ozone depletion.
In March 2020, shortly after the fires subsided, the team observed a sharp drop in nitrogen dioxide in the stratosphere.
The researchers found that this drop in nitrogen dioxide was directly related to the amount of smoke that fires released into the stratosphere. This smoke-induced chemistry depleted the ozone column by 1 percent. This is the same percentage that the ozone layer has recovered over the past decade. thanks to international agreements signed to stop its destruction.
This means that wildfires have reclaimed hard-won international successes within a short period of time. If future wildfires become stronger and more frequent as climate change predicts, projected ozone recovery could be delayed for years.
“The Australian fires seem to be the biggest event of its kind to date, but as the world continues to warm, there is every reason to think about it. these fires will be more frequent and severe“Just like the Antarctic ozone hole, it’s another wake-up call,” said lead author Susan Solomon, the Lee and Geraldine Martin Professor of Environmental Studies at MIT.
Smoke up to the stratosphere
Large wildfires are known to produce pyrocumulonimbus clouds, which are towering clouds of smoke that can reach the stratosphere, the layer of atmosphere located about 15 to 50 kilometers above the Earth’s surface. Smoke from Australian bushfires reached up to 35 kilometers into the stratosphere.
In 2021, study co-author Pengfei Yu of Jinan University conducted a separate study on the effects of fires and found that the accumulated smoke heated parts of the stratosphere by up to 2 degrees Celsius, which continued for six months. The study also found signs of ozone destruction in the southern hemisphere after fires.
Solomon wondered if the smoke from the fires depleted ozone through chemistry similar to volcanic aerosols. Large volcanic eruptions can also reach the stratosphere, and in 1989 Solomon discovered that particles from these eruptions can destroy ozone through a series of chemical reactions.
Just like volcanic eruptions
In the new study, Solomon and colleagues examined how nitrogen dioxide concentrations in the stratosphere changed after the Australian fires. If these concentrations drop significantly, that would be a sign. Smoke from forest fires depletes ozone through the same chemical reactions as some volcanic eruptions.
The team analyzed nitrogen dioxide observations taken by three independent satellites surveying the southern hemisphere for varying periods of time. They compared recordings from each satellite in the months and years before and after the Australian fires. All three records Significant decrease in nitrogen dioxide in March 2020.
To confirm that the drop in nitrogen dioxide is the direct chemical effect of smoke from fires, the researchers ran atmospheric simulations using a spherical 3D model that simulates hundreds of chemical reactions in the atmosphere, from the surface to the stratosphere.
Now scientists are investigating other reactions triggered by smoke from forest fires that may further contribute to ozone depletion. For now, the main driver of ozone depletion remains chlorofluorocarbons, or CFCs, which are chemicals like old-fashioned refrigerants banned under the Montreal Protocol, although they remain in the stratosphere. But as global warming leads to stronger and more frequent forest fires, their fumes can have a serious and long-lasting effect on ozone.
“Bushfire smoke is a toxic mixture of organic compounds that are complex beasts”Solomon says. “And I’m afraid ozone is being affected by a number of reactions that we’re frantically trying to solve right now,” he adds.
Reference article: https://news.mit.edu/2022/wildfire-smoke-ozone-depletion-0228
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