Nitrous oxide Greenhouse Gas
By Caitlin Frame :: Originally published online : In print Vol. 47, No. 1, Dec. 2008
There’s a greenhouse gas whose concentration is on the rise because of human activities. But it’s not the one you’d expect: it’s nitrous oxide (N2O), also known as laughing gas. It’s been accumulating in the atmosphere since the 1700s, and it’s powerful and persistent. One molecule of N2O has the same greenhouse warming power of 300 molecules of carbon dioxide. Once that N2O molecule gets into the upper atmosphere, it can stay there for more than 100 years before it’s destroyed naturally.
Fortunately, air has about 1, 000 times less N2O than carbon dioxide. But the rise in N2O has accelerated over the past two decades. And while we know where the excess carbon dioxide is coming from, we don’t know precisely how N2O is produced. That’s information we’ll need to know in order to curb future N2O production.
“As the U.S. gets serious about controlling greenhouse gas emissions, we need to figure out how and where N2O is made, ” said Kevin Kroeger, a scientist at the U.S. Geological Survey (USGS) in Woods Hole.
Every year an estimated 17 million tons of nitrogen are released to the atmosphere as N2O, according to the International Panel on Climate Change. The source of more than half of this N2O is probably soil, where scientists have tended to focus their studies. The rest comes from the ocean—where measurements have been harder to make. But as we take a closer look, we are realizing that N2O production in the ocean is more important than we used to think.
“People are realizing that soil isn’t the end of the N2O story, ” said USGS scientist John Crusius. Kroeger, Crusius, and colleagues John Bratton and Eric Sundquist are leading efforts to measure coastal N2O emissions. The USGS team seeks to answer questions such as: Where is the coastal N2O coming from and how much is there?
At the Woods Hole Oceanographic Institution (WHOI), we’re investigating other pieces of the puzzle: Which organisms are making N2O in the ocean? How are they doing it? Are ocean conditions changing to produce more N2O?
In the oceans and in soil, the primary players are microbes, which, as they go about their lives, transform certain nitrogen compounds into N2O. Humans have dumped huge amounts of these compounds into the soil and coastal waters, sending the microbes into N2O overdrive.
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