Greenhouse Gas Recycles as It Cleans Atmosphere
By Christina Phillis.
As researchers continue to refine their climate change models to make more reliable predictions, a simple molecule may play a significant part. The hydroxyl radical (•OH), which is known to break down other greenhouse gases, has been found to maintain or “recycle” itself in the atmosphere according to a study by NASA researchers. Its sources and ability to replenish itself are important to note when trying to predict future amounts of greenhouse gases in our atmosphere.
Simple yet Mighty
Researchers were primarily interested in studying the hydroxyl radical because of its ability to change the lifetime of other gases, including methane which is second only to carbon as a contributor to global warming. This simple molecule is just a combination of one hydrogen atom and one oxygen atom with a free electron.
Before examining the results of this study, scientists believed that the hydroxyl radical would be removed from the atmosphere as it interacted with methane, especially with increasing methane emissions. However, when surrounded by other gases, the hydroxyl radical remained. "When OH reacts with methane it doesn't necessarily go away in the presence of other gases, especially nitrogen oxides (NO and NO2),” said atmospheric chemist and lead author Julie Nicely, PhD. After it reacts with methane, the products react with the nitrogen oxides to again form hydroxyl radicals.
"Our ability to resolve hydroxyl won’t revolutionize climate models, but it’ll increase our confidence in them."
To better understand the various sources of hydroxyl radicals, NASA researchers used a computer model of satellite observations to study various gases during the period from 1980 to 2015. A new potential source of hydroxyl radicals stood out: the growing tropical regions of the Earth.
The tropics appear to be expanding because of the rising temperatures that affect air circulation patterns. The tropics are also prime spots for hydroxyl radical creation because of the abundance of water vapor and ultraviolet sunlight. When light enters the atmosphere and reacts with water vapor and ozone, two hydroxyl radical molecules are formed. The increase in tropical climates due to global warming has the potential to increase the level of hydroxyl radical in the atmosphere.
Although these additional sources of hydroxyl radicals are relatively small, study researchers say they have a big impact on replenishing the hydroxyl radicals used when breaking down methane. Goddard Atmospheric Chemist Tom Hanisco said there’s no guarantee hydroxyl radical levels will continue to recycle in the same way as the atmosphere evolves with climate change. However, Dr. Nicely believes these results will help us better refine and predict the interactions of these two gases in the atmosphere, a major deciding factor in future climate change.
Drilling for Answers
Complementing the NASA study is a separate project staffed by Australian and U.S. researchers, who are venturing to Antarctica to gather historical data on concentrations of hydroxyl radicals. To capture samples that represent what the atmosphere was like before global warming, the team will extract air bubbles from 230-meter deep ice cores. As the hydroxyl radical only lasts for a second before it reacts with other gases, they will use Carbon-14 in carbon monoxide as a proxy.
To date, scientists have only used atmospheric models for determining hydroxyl radical levels. According to these models, concentrations have remained stable over the past 120 years and started to increase with warming trends in the 1970s. The Antarctic researchers believe their work will help confirm the trends predicted by the atmospheric models.
“Our ability to resolve hydroxyl won’t revolutionize climate models, but it’ll increase our confidence in them,” said Matt Woodhouse, a climate modeler at CSIRO.
Research projects like these confirm that even the smallest details can help in the fight against climate change. Our ability to understand the simple hydroxyl radical can have a big impact on our understanding of global warming.
