It’s long been thought that sulfur dioxide emissions from things like coal-burning power plants need to react in sunlight to make sulfuric acid in the atmosphere. But a new discovery suggests there might be more to the story.
Scientists likeLee Mauldin, a researcher at the University of Colorado in Boulder and the University of Helsinki, thought they had the production of sulfuric acid in the atmosphere pretty much figured it out.
“Sunlight shines down and blows apart ozone,”says Mauldin.
The broken ozone in turn creates hydroxyl radicals (OH) that are highly reactive and are the primary oxidant in the atmosphere.
Until recently, the hydroxyl radical was the only compound known to react with sulfur dioxide, or SO2, to make sulfuric acid. And because the sun sparks this reaction, it was thought that sulfuric acid could only be made during the daytime.
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But Mauldin and his colleagues saw plenty of sulfuric acid being made at night when they took measurements in a forest in Finland. Without the presence of hydroxyl radicals, how was the acid being made?
“We found a new oxidant that reacts all day long, 24/7, and is capable of turning SO2 into sulfuric acid,” says Mauldin, who published the results in the journal Nature on Aug. 9.
“To discover something that could open up a whole new arena in oxidation chemistry,” says Mauldin, “it’s a once in a lifetime kind of event or finding.”
It looks like the hardworking oxidant is a result of ozone interacting with fragrant compounds made by spruce and pine trees called terpenes.But why would trees be capable of contributing to a such a chemical reaction? Mauldin thinks it could be part of a feedback mechanism to control climate.
“Sulfuric acid is responsible for the formation of aerosols,” explains Mauldin. “The initial particles are like a nanometer or less in size, and then they will eventually grow up to be things that could form clouds.”
And clouds can reflect light back to into space, which has a cooling effect on the environment. So as the climate gets hotter, Mauldin says trees may naturally be making more terpenes to knock down the temperature.
“The US over the last 100 years has basically kind of experienced a warming, overall,” says Mauldin. “However in the Southeast there’s actually been a slight cooling.”
Mauldin suspects the forests in the Southeast have actually driven this chill by increasing cloud cover using his newly discovered chemical reaction.
