The way it unfolds the OH in the atmosphere considered a complete story, but in new research published in Annals of the National Academy of Sciencesa research team that includes Serguei Nizkorodovprofessor of chemistry at the University of California at Irvine, reports that the strong electric field that exists at the surface between water droplets in the air and the surrounding air can create OH by a previously unknown mechanism.
It’s a discovery that will change the way scientists understand how the air is cleaned of things like man-made pollutants and greenhouse gases, with which OH can react and eliminate. “OH is needed to oxidize hydrocarbons, otherwise they would build up in the atmosphere indefinitely.“Nizkorodov said.
The role of OH in the atmosphere
“OH is a key player in the history of atmospheric chemistry. Starts reactions that break down pollutants in the air and helps remove harmful chemicals like sulfur dioxide and nitric oxide, which are poisonous gases, from the atmosphere“, he said Cristiano Jorge, an atmospheric chemist at the University of Lyon in France and lead author of the new study. “Therefore, having a complete understanding of its sources and sinks is critical to understanding and mitigating air pollution.“.
Previously, researchers assumed that sunlight was the main factor in the formation of OH.
“Conventional wisdom is that you have to make OH by photochemistry or chemistry. You need to have sunlight or metals that act as catalysts“Nizkorodov said.”What this document basically says is that you don’t need any of that. In pure water, OH can be created spontaneously by special conditions on the surface of droplets“.
The team relied on research by scientists at Stanford University, led by Richard Zare, who reported the spontaneous formation of hydrogen peroxide on the surface of water droplets. The new findings help interpret the Zare group’s unexpected results.
The team measured OH concentrations in different flasks, some containing a surface of air and water and others containing just water without air, and tracked OH production in the dark by including a “probe” molecule in the flasks that fluoresces when it reacts with OH. .
What they saw is that Rates of OH production in the dark mirror and even exceed rates in conductors such as exposure to sunlight. “Enough OH will be created to compete with other known sources of OH“Nizkorodov said.”At night, when there is no photochemistry, OH is still produced, and it is produced at a higher rate than it would otherwise be.“.
The findings, Nizkorodov reported, change our understanding of OH sources, something that will change the way other researchers build computer models that try to predict how air pollution occurs.
“It could change air pollution patterns quite significantly.“Nizkorodov said.”OH is the main oxidant in water droplets and the main assumption in the models is that OH comes from the air, it is not produced directly in the droplet.“.
To determine whether this new OH production mechanism plays a role, Nizkorodov believes the next step is to conduct carefully designed experiments in the real atmosphere in different parts of the world.
But first, the team hopes the results will cause a sensation in the atmospheric research community.
“Many people will read this but initially will not believe it and will either try to reproduce it or try to do experiments to prove it wrong.“Nizkorodov said.”There will certainly be many lab experiments after this.“.
He added that the UCI is a privileged place for this science to continue to take place, because other laboratories at the UCI, such as chemistry professor Ann Marie Carlton, focus their efforts on the role of water droplets in the atmosphere.
Kangwei Li et al. Spontaneous dark formation of OH radicals at the interface of aqueous atmospheric droplets, Annals of the National Academy of Sciences (2023). DOI: 10.1073/pnas.2220228120