Image from Ray Weiss
When it comes to ranking anthropogenic greenhouse gases based on their warming potential, carbon dioxide actually falls pretty low on the list -- the problem is that there's just too damn much of it. Thankfully, the atmospheric concentrations of far more potent GHGs, such as nitrous oxide and methane, have not yet followed carbon dioxide's dramatic ascent over the last half-century (though there are some concerns methane levels could soon begin to spike if present trends continue).
Though their combined contribution to the global warming effect may still be low, scientists have been dismayed to learn that their estimates for current and future levels, once considered fairly reliable, have often fallen off the mark. A case in point is a new study led by a team of researchers from the Scripps Institution of Oceanography that has found that levels of nitrogen trifluoride (NF3), an extremely potent greenhouse gas (almost 17,000 times more potent than an equivalent mass of carbon dioxide on a 100-year time horizon), are at least four times higher than previously thought.
NF3: not as innocuous as previously thought
Nitrogen fluoride is typically used during the manufacture of LCD displays, microcircuits and thin-film solar cells as an alternative to perfluorocarbons (PFCs), another well-known class of greenhouse gases. Because it was thought that no more than 2 percent of emissions found their way into the atmosphere, NF3 was never considered a major contributor to climate change; indeed, it isn't even covered by the Kyoto Protocol. (NF3 emissions only contribute about 0.15 percent of the global warming effect contributed by carbon dioxide emissions.)
To measure current and past emission levels, the Scripps researchers studied air samples gathered by a network of NASA-funded clean-air stations in California and Tasmania (part of the agency's Advanced Global Atmospheric Gas Experiment network) over the last 3 decades. They used a method that combined the use of chromatography and mass spectrometry to separate NF3 from other volatile atmospheric gases, such as krypton and carbon dioxide, in order to receive more accurate results.
11% annual growth since 1978
The scientists found that the average global tropospheric concentration of NF3 rose quasi-exponentially from roughly 0.02 ppt (parts per trillion) in 1978, when measurements first began, to 0.454 ppt in July 2008; this represents an annual increase of about 0.053 ppt (equivalent to the release of about 620 metric tons of NF3), or 11 percent per year. Not surprisingly, the air samples revealed that there were significantly greater concentrations of NF3 in the Northern Hemisphere than in the Southern Hemisphere.
According to lead author Ray Weiss, a professor of geochemistry, previous estimates, which relied on now dated techniques, had pegged the amount of atmospheric NF3 at 1,200 metric tons in 2006; the actual amount was 4,200 metric tons. The amount has since increased to 5,400 metric tons.
"From a climate perspective, there is a need to add NF3 to the suite of greenhouse gases whose production is inventoried and whose emissions are regulated under the Kyoto Protocol, thus providing meaningful incentives for its wise use," said Weiss. While not a disastrous finding in of itself, this study does reinforce the need to always err on the cautious side when relying on emission estimates and underlines the importance of a broad, multifaceted approach that targets all greenhouse gases effectively.
Via Green Car Congress: New Study Finds Atmospheric Levels of GHG NF3 At Least 4x Higher Than Previously Estimated
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