New research by Glenn Wolfe and UMBC staff has shown how scientists understand the fate of methane, a powerful greenhouse gas, in the Earth's atmosphere.
Of the greenhouse gases, methane has the third largest overall effect on the climate after carbon dioxide and water vapor. And the longer it stays in the atmosphere, the more heat it stores. For this reason, it is essential for climate models to adequately map the life of methane until it is degraded. This happens when a methane molecule with a hydroxyl radical ̵
"OH is actually the most central oxidant in the lower atmosphere, controlling the lifetime of almost all reactive gases," says Wolfe, research associate at UMBC Systems Engineering's Joint Center for Earth. "Globally, however, we have no way to directly measure OH." In addition, it is clear that current climate models have difficulty accurately simulating OH. With existing methods, scientists can roughly conclude OH, but there is little information about where, when, and why OH varies.
New research published in Proceedings of the National Academy of Sciences and headed by Wolfe, scientists are well on the way to change this. Wolfe and colleagues have developed a unique method to conclude how global OH concentrations differ over time and in different regions. A better understanding of OH levels can help scientists understand how the ups and downs in global methane levels are due to changing emissions, such as oil and gas production or wetlands, compared to OH levels.
A Flying Lab
NASA satellites have been measuring atmospheric formaldehyde concentrations for over 15 years. Wolfe's new research draws on this data as well as new observations collected during NASA's recent mission in Atmospheric Tomography (ATom). ATom has flown four cycles around the world using a NASA research aircraft and taken air samples.
This "flying laboratory," as Wolfe describes it, collected data on atmospheric formaldehyde and OH contents, illustrating a remarkably simple relationship between the two gases. This did not surprise the scientists, since formaldehyde is a major by-product of methane oxidation. However, this study provides the first concrete observation of the correlation between formaldehyde and OH. The results also showed that the formaldehyde concentrations in the measured plane coincided with those measured by the satellites. In this way, the Wolfe team and others can use the existing satellite data to deduce the OH values in most areas of the atmosphere.
"The measurements in the air give you the truth that this relationship exists," Wolfe says, "and the satellite measurements allow this to extend this relationship around the globe."
However, Wolfe is the first to recognize that the work to improve global models is far from over. The aircraft measured OH and formaldehyde levels over the open ocean, where the air chemistry is relatively simple. Over a forest and especially over a city it would be more complicated.
While the relationship researchers identified provides a solid baseline, as much of the Earth's air actually floats over the oceans, more work is needed to see how the OH levels differ in more complex environments. Other data from existing NASA satellites, such as those used to track emissions from urban areas or forest fires, may be helpful.
Wolfe hopes to further refine this work, which in his view lies in the "Nexus of Chemical and Climate Research Communities". And they are very interested in getting OH right.
Getting it Right
The current study took into account seasonal variations in OH by analyzing the measurements made in February and August. "Seasonality is an important aspect of this study," says Wolfe, " because the latitude at which OH is at its maximum moves. "Considering seasonal shifts in OH concentrations or even perennial shifts caused by phenomena such as El Niño and La Niña could be a starting point for improving global climate models.  Further consideration of OH values on a global scale using satellite data validated with aircraft data could also help scientists to refine their models. "They can use spatial variability and seasonality to understand at the process level what drives OH, and then ask if the model is right or not, "says Wolfe The idea is to be able to use all those features we have not had data for yet. "
This new research is a step towards a better understanding of the global climate, even if it's fast changes. Greater understanding of how reducing methane emissions, for example, affects the climate and how quickly this could impact policy decisions. "But the potential is there."
US. Methane emissions have remained constant since 2006 despite increased oil and gas activity
Glenn M. Wolfe et al., Mapping of Hydroxyl Variability in the Global Remote Troposphere by Synthesis of Air and Satellite Formaldehyde Observations Proceedings of the National Academy of Sciences (2019). DOI: 10.1073 / pnas.1821661116
Team develops new method to measure the ability of the atmosphere to remove methane, a powerful greenhouse gas (2019, June 3)
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