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 (OH) radical, 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 hydroxyl because of its ability to change the lifetime of other gases, including methane, 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 hydroxyl would be removed from the atmosphere as it interacted with methane, especially with increasing methane emissions. But when surrounded by other gases, hydroxyl 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 OH.

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 OH, 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 OH 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 OH creation because of the abundance of water vapor and ultraviolet sunlight. When light enters the atmosphere and reacts with water vapor and the ozone, two OH molecules are formed. The increase in tropical climates due to global warming has the potential to increase the level of OH in the atmosphere.

Although these additional sources of OH are respectively small, study researchers say they have a big impact, replenishing the OH used when breaking down methane. Goddard Atmospheric Chemist Tom Hanisco said there’s no guarantee OH levels will continue to recycle in the same way as the atmosphere evolves with climate change. But 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. 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. Because hydroxyl 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 used only atmospheric models for determining hydroxyl 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 molecule can have a big impact on our understanding of global warming. 

Clouds Rolling Over a Field