Air chemistry data from field study in South Korea puts models to the test
According to a team of scientists, an international effort to measure air quality in South Korea, a region with complex sources of pollution, could provide new insights into the atmospheric chemistry that produces ozone pollution.
“This study shows that observations of the hydroxyl radical — OH — and the hydroperoxyl radical — HO2 provide valuable tests of the ability of our photochemical models to correctly represent atmospheric chemistry, especially in high pollution environments. “said William H. Brune, distinguished professor of meteorology at Penn State.
The hydroxyl radical initiates important chemical reactions throughout the atmosphere, including the troposphere, the lowest region reaching the Earth’s surface, where its reactions purify the air but also lead to ozone pollution. in cities, the scientists said.
The team analyzed airborne measurements of the hydroxyl radical, hydroperoxyl radical and about 100 other chemical species taken during flights over South Korea in 2016 as part of a joint field study between NASA and the Republic of Korea, called Korea-US Air Quality (KORUS-AQ).
The airborne measurements of hydroxyl and hydroperoxyl radicals were consistent with values produced by separate models run at NASA’s Langley Research Center and at Penn State when uncertainties in the measurements and models are taken into account, the researchers said.
“A major discovery is – even in a complex environment like this – we have a good grasp of the basic chemistry of our models,” Brune said. “We can really say that this chemistry is correct within the uncertainties, and that tells us something about ozone production.”
Ozone forms when oxides of nitrogen – such as emissions from vehicles and power plants – and volatile organic compounds – produced naturally by plants but also by solvents and other harsh man-made chemicals – combine mix into the atmosphere in the presence of sunlight, scientists say.
“But these elements can’t do much on their own, they need something to make the chemistry active, and that’s the hydroxyl radical,” Brune said. “It drives the chemistry, kind of like a low-temperature version of the flame that heats your house.”
While the hydroxyl radical measured during the flights was generally in agreement with the models, the scientists found less agreement when they looked at their measurements of the reactivity of the radical, which is the sum of the reactions between the hydroxyl radical and all chemical species.
“That’s really a key number because a very high reactivity of the hydroxyl radical means you’re in a very polluted environment, or an environment that emits a lot of things that react with the hydroxyl radical,” Brune said.
When the measured hydroxyl radical reactivity was compared to the calculated hydroxyl radical reactivity using all other measurements, it was not possible to account for up to half of the hydroxyl radical reactivity in some cases. , said the scientists, who reported their findings in the journal Atmospheric Environment.
This missing hydroxyl radical reactivity came mostly from the Korean peninsula, potentially helping to distinguish sources between pollution emitted by industry in South Korea and older pollution blowing in from China, the scientists said.
“We came up with this idea of measuring the reactivity of hydroxyl radicals about 25 years ago, and we found missing reactivity in forests and all sorts of other places,” Brune said. “And while we’re now much better at bridging the gap between measured and calculated hydroxyl radical reactivity, in South Korea we thought we were measuring everything, and we clearly weren’t measuring everything.”
Improving our understanding of this reactive chemistry is important, Brune said, because this information can inform regional and global air quality patterns.
“These models have a hard time predicting really harmful amounts of ozone,” he said. “I hope our results will help them understand the problem so they can be used by policymakers to effectively reduce ozone levels, not just in the United States, but around the world.”
Other Penn State researchers on this project were David Miller, assistant research professor, and graduate students Alexander Thames and Alexandra Brosius.
Scientists from the University of California Irvine, NASA Langley Research Center, University of Colorado Boulder, NASA Goddard Space Flight Center, Georgia Institute of Technology, California Institute of Technology, University of Virginia, University of Innsbruck and University of Oslo also participated.
NASA funded several researchers involved in the study.