Some scientists propose using sulfur compounds to create a sun shield in the upper atmosphere to address climate change. There is a good deal more chemistry to be understood before moving forward. The laboratory in Francisco.
With climate change so difficult to manage and nations unwilling to take decisive action, what if we could mitigate its effects by setting up a kind of chemical umbrella that could reflect the sun's radiation and cool the Earth?
The production of sulfuric acid is less efficient due to the challenge of generating it in the stratosphere, according to a new study in the Journal of the American Chemical Society. The researchers say that more groundwork is needed in order to confidently move forward with this climate engineering strategy.
The study shows the importance of understanding the photochemistry involved in engineering, says Joseph S. Francisco, an atmospheric chemist in Penn's School of Arts & Sciences. It's something that has been ignored.
When volcanoes erupt, the sulfur they emit creates cooling clouds that block the sun's rays. The clouds come from the troposphere, which is about 10 kilometers up. From about 10 to 20 kilometers above the planet, sulfuric acid would be used forgeoengineering.
As the altitude increases, the conditions change. The air becomes less humid and the sun's rays become stronger. Francisco and his colleagues from Spain's Rocasolano Institute of Physical Chemistry and the University of Valncia collaborated to explore how variables affect the chemical reactions involved in making sulfuric acid.
The major inputs are sulfur dioxide and OH. HOSO2 reacts with oxygen to create sulfur trioxide, which then reacts with water to create sulfuric acid. The sulfuric acid can reflect sunlight.
The reactions are responsible for creating acid rain in the troposphere. It was not known if that chemistry would work in the high altitude.
The team used quantum chemistry to find out how HOSO2 and SO3 would behave in the high light and low humidity conditions of the stratosphere. The researchers found that when HOSO2 is produced in the stratosphere, solar radiation causes the molecule to photolyze, breaking apart into its component parts, which is harmful to humans.
The Penn-led group found that HOSO2 would break apart in the stratosphere, likely reducing the efficiency of producing sulfuric acid at those altitudes. The laboratory in Francisco.
Francisco says that if you put sulfur dioxide up there, it's going to be recycled. It opens the door to the question of whether we have a full understanding of atmospheric sulfur chemistry up in the sky.
Reducing HOSO2 would affect the efficiency of producing sulfuric acid, the researchers note.
The researchers found that SO3 levels remained stable. Francisco says that they know it reacts with water, but they don't know how it will react. Will the atmosphere find a way to get rid of the SO3 or will it collect somewhere and start new chemistry?
The researchers note that it's crucial to understand what other reactions these molecules could be entering into. He says that the work points to a cautionary note: if the SO3 chemistry is different, how does it interact with the other chemistry that's currently going on in the stratosphere. We need to think about whether there are any chemical concerns up front.
The need for a Plan B is highlighted by the findings. Francisco says it raises a fundamentally important question. Can we get the sulfur dioxide out of the air?
Francisco's group is working on applying cutting-edge quantum methodologies to examine how photochemistry interacts with atmospheric models to generate a more complete understanding of various geoengineering scenarios.
Francisco says that this is the first time that you're taking results from fundamental physics and chemistry and mapping them into climate models to look at the three-dimensional atmospheric impact.
Francisco and his colleagues emphasize that the outcomes depend on some aspects of sulfur chemistry that are unknown.
Francisco says that this brings to the forefront the need to make the community aware that there's more fundamental chemistry that we need before we start to understand the full chemical impact of this approach.
The Journal of the American Chemical Society has more information about the photochemistry of HOSO2 and SO3. There is a DOI: 10.1021/jacs.1c10153.
The Journal of the American Chemical Society has information.
Researchers must consider some fundamental chemistry before they can think of ways to mitigate climate change.
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