Study reveals chemical link between wildfire smoke and ozone depletion

For how long and powerfully the Australian wildfires burned in 2020 and how far and fast they spread were historic. More than 43 million acres of land were burned in the Black Summer fires. The fires injected over 1 million tons of smoke particles into the atmosphere, which reached up to 35 kilometers above Earth's surface.

The smoke from those fires set off chemical reactions in the atmosphere that led to the destruction of ozone, which protects the Earth from the harmful rays of the sun. The team's study is the first to show a link between ozone and wildfire smoke.

The team observed a drop in nitrogen dioxide in the air after the fires had ended, which is the first step in a chemical cascade that is known to end in ozone depletion. The researchers found that the drop in nitrogen dioxide was related to the amount of smoke in the air. They think that smoke-generated chemistry depletes the column of ozone by 1 percent.

They note that the phaseout of ozone-depleting gases under a worldwide agreement to stop their production has led to about a 1 percent ozone recovery from earlier ozone decreases over the past 10 years. Ozone's projected recovery could be delayed by years if future wildfires grow stronger and more frequent as predicted by climate change.

The Australian fires look like the biggest event so far, but as the world continues to warm, there is every reason to think these fires will become more frequent and more intense.

Kane Stone is a research scientist in the Department of Earth, Atmospheric, and Planetary Sciences at MIT.

The trace is chemical.

Towering clouds of smoke that can reach into the stratosphere, the layer of the atmosphere that lies between 15 and 50 kilometers above the Earth's surface, are generated by massive wildfires. The smoke from the fires in Australia reached as high as 35 kilometers above the ground.

In 2021, Solomon and his co-author, Pengfei Yu at Jinan University, carried out a study of the impacts of the fires and found that the smoke warmed parts of the stratosphere by as much as 2 degrees Celsius. The study found evidence of ozone destruction in the Southern Hemisphere.

Solomon wondered if the smoke from the fires could have damaged ozone. Solomon discovered in 1989 that volcanic eruptions can destroy ozone through a series of chemical reactions. As the particles form in the atmosphere, they collect water on their surfaces. Once wet, the particles can react with circulating chemicals in the stratosphere, including dinitrogen pentoxide, which reacts with the particles to form nitric acid.

Nitrogen dioxide, a compound that bonds with chlorine-based chemicals in the stratosphere, is formed when dinitrogen pentoxide reacts with the sun. When volcanic smoke converts dinitrogen pentoxide into nitric acid, nitrogen dioxide drops, and chlorine compounds take another path, they become chlorine monoxide, the main human-made agent that destroys ozone.

Solomon says that once you get past that point, the chemistry is well-established.

There is a cloud injection.

Solomon and her colleagues looked at how nitrogen dioxide concentrations changed after the Australian fires. If the concentrations dropped, it would show that the smoke from the fires depletes ozone.

The team looked at the nitrogen dioxide observations taken by three independent satellites. They compared the records of each satellite in the months and years leading up to and following the Australian fires. The records showed a drop in nitrogen dioxide. For one satellite, the drop was a record low.

The researchers used a global, three-dimensional model to model hundreds of chemical reactions in the atmosphere to see if the nitrogen dioxide decrease was caused by the fires.

The team injected a cloud of smoke particles into the model to make it look like the Australian wildfires. They assumed that the particles gathered the same amount of water as volcanic aerosols. They ran the model multiple times and compared the results to simulations without the smoke cloud.

The team found that as the amount of smoke particles increased in the sky, the concentrations of nitrogen dioxide decreased.

Solomon says that the behavior of more and more aerosols, and less and less nitrogen dioxide, in both the model and the data, is a fantastic fingerprint. It may only be one chemical mechanism, but it is clearly there. It tells us that the particles had to have caused ozone damage.

She and her partners are looking into the effects of wildfire smoke on other reactions. chlorofluorocarbons, or CFCs,chemicals that have been banned under the Montreal Protocol, are still the main driver of ozone depletion. As global warming leads to stronger, more frequent wildfires, their smoke could have a serious impact on ozone.

Solomon says that wildfire smoke is a toxic brew of organic compounds that are complex beasts.

More information: On the stratospheric chemistry of midlatitude wildfire smoke, Proceedings of the National Academy of Sciences (2022). doi.org/10.1073/pnas.2117325119 Journal information: Proceedings of the National Academy of Sciences Citation: Study reveals chemical link between wildfire smoke and ozone depletion (2022, February 28) retrieved 28 February 2022 from https://phys.org/news/2022-02-reveals-chemical-link-wildfire-ozone.html This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only.