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Though geoengineering approaches factor in the ability of these two molecules to reflect sunlight, the researchers found that when HOSO 2 is produced in the stratosphere, solar radiation causes the molecule to quickly photolyse, essentially breaking apart into its component parts, including sulfur dioxide, which is harmful to humans in high concentrations. To find out, the team used quantum chemistry-an approach that considers the ground, transition, and excited states of atoms and molecules-to consider how HOSO 2 and SO 3 would behave in the stratosphere’s conditions of high light and low humidity.
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(Image: Courtesy of the Francisco laboratory) Research by the Penn-led group indicated that HOSO2 would photolyse, or break apart, in the stratosphere, likely reducing the efficiency of producing sulfuric acid at those altitudes. But whether that chemistry would work in the stratosphere and achieve the same efficiency was unknown. These reactions are well-characterized together, they are responsible for creating acid rain in the troposphere. Aerosols formed from the sulfuric acid have the ability to reflect sunlight. HOSO 2 reacts with oxygen to create sulfur trioxide (SO 3), which then reacts with water vapor to create sulfuric acid. The major inputs are sulfur dioxide (SO 2), which reacts with hydroxide (OH), a kind of atmospheric “detergent,” to create HOSO 2.
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In the new work, Francisco, his postdoc Tarek Trabelsi, and colleagues from Spain’s Rocasolano Institute of Physical Chemistry and the University of València partnered to explore how these variables affected the chemical reactions involved in making sulfuric acid. Notably, the air becomes drier, and the energy of the sun’s rays becomes stronger.
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Geoengineering using sulfuric acid would happen a good deal higher, in the stratosphere, from about 10 to 20 kilometers above the planet.Ĭonditions change as the altitude increases. But those clouds emerge in the troposphere, which ranges from the Earth’s surface to about 10 kilometers up. Using sulfuric acid to blunt the sun’s rays as a means of curbing climate change impacts is based on a natural phenomenon: When volcanoes erupt, the sulfur they emit creates localized-or sometimes even far-reaching-cooling clouds that filter the sun. “That’s critically important and it’s something that’s been ignored.” Francisco, an atmospheric chemist in Penn’s School of Arts & Sciences and a co-corresponding author on the study. “These fundamental insights highlight the importance of understanding the photochemistry involved in geoengineering,” says Joseph S. Thus more groundwork exploring the chemistry of how sulfuric acid and its building blocks will react in the upper atmosphere is required in order to confidently move forward with this climate geoengineering strategy, the researchers say. It’s a tempting thought: 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-a layer of sulfuric acid in the upper atmosphere that could reflect the sun’s radiation and cool the Earth?Īccording to a new study in the Journal of the American Chemical Society, a collaboration among Penn scientists and two groups in Spain, atmospheric conditions in the stratosphere pose a challenge to generating sulfuric acid, making its production less efficient than might have previously been expected. New research suggests there’s a good deal more chemistry to understand before proceeding. Some scientists have proposed planetary-scale solutions to address climate change, such as geoengineering using sulfur compounds to create a sunshield in the upper atmosphere.