A simple molecule in the atmosphere that acts as a "detergent" for the removal of methane and other greenhouse gases recycles itself to maintain a constant global presence in the face of rising emissions, NASA's new research suggests. Understanding its role in the atmosphere is critical to determining the lifetime of methane, which contributes significantly to climate change.
The hydroxyl (OH) radical, a molecule consisting of a hydrogen atom, an oxygen atom, and a free (or unpaired) electron, is one of the most reactive gases in the atmosphere and regularly breaks down other gases, effectively degrading them Lifeshiles In this way, OH is the main test of methane concentration, a powerful greenhouse gas that only adds to carbon dioxide to increase global temperatures.
With the increase in methane emissions into the atmosphere, scientists felt that this might be the case for consuming the amount of hydroxyl radicals on a global scale, thereby extending the life of methane, which is currently estimated at nine years. The new research takes into account not only the primary OH sources and the amount of methane and other gases that are being mined, but also the secondary OH sources, recycling after OH has degraded methane, and reforms in the presence of others Gases
"OH concentrations are fairly stable over time," said atmospheric chemist and lead author Julie Nicely at NASA's Goddard Space Flight Center in Greenbelt, Maryland. "When OH reacts with methane, it is not necessarily lost in the presence of other gases, especially nitrogen oxides (NO and NO 2 ) .The degradation products of their reaction with methane react with NO or NO 2 [1
Nitrogen oxides are a set of multiple gases that contribute to the recycling of OH to the atmosphere, according to Nicely's findings in the Journal of Geophysical Research: Atmospheres . She and her colleagues used a computer model that was informed by satellite observations of various gases from 1980 to 2015 to simulate the possible sources of OH in the atmosphere. These include reactions with the aforementioned nitrogen oxides, water vapor and ozone. They also tested an unusual potential source for new OH: the enlargement of the tropical regions of the earth.
OH in the atmosphere also forms when ultraviolet sunlight reaches the lower atmosphere and reacts with water vapor (H 2 O) and ozone (O 3 ) to produce two OH To form molecules. In the tropics, there is plenty of water vapor and ultraviolet sunlight. The tropics that extend across the earth on either side of the equator have shown some signs of expanding further north and south of their present range, possibly due to rising temperatures affecting air circulation patterns. This means that the tropical region designed to produce OH may increase over time, resulting in a higher amount of OH in the atmosphere. This tropical distribution process is slow but only 0.5 to 1 degree wide every 10 years. The small effect, however, may still be important, according to Nicely.
She and her team found that the tropical broadening effect and OH recycling from reactions with other gases are each a relatively small source of OH, but together they essentially replace the OH consumed in methane mining.
"The absence of a trend in global OH is surprising," said atmospheric chemist Tom Hanisco of Goddard, who was not involved in the research. "Most models predict a" feedback effect "between OH and methane, OH also removes OH with methane, increasing NO 2 and other OH sources, such as ozone "This is an anticipated effect." However, as this study looks at the past thirty-five years, it can not be guaranteed that the atmosphere will continue to evolve with global climate change and that OH levels will be recycled the same way in the future.
You can look at the results very well as a method of fine-tuning and updating the assumptions of researchers and climate modellers who describe and predict how OH and methane interact in the atmosphere. "This could help to clarify whether methane levels will continue to increase in the future, or will they decrease or even decrease, which is an important issue regarding the future climate, to which we do not really know the answer," she said ,
First direct observations of the increasing greenhouse effect of methane on the earth's surface
Julie M. Nicely et al. Changes in the Global Tropospheric Climate Zone Expected as a Result of Climate Change in Recent Decades Journal of Geophysical Research: Atmospheres (2018). DOI: 10.1029 / 2018JD028388