Solar cells, flat-panel screens are source of potent greenhouse gas

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Solar cells, flat-panel screens are source of potent greenhouse gas
mongabay.com
October 23, 2008

Solar cells, flat-panel screens are source of greenhouse gas 17,000 times more potent than CO2

Atmospheric concentrations of nitrogen trifluoride — a gas used in the manufacture of liquid crystal flat-panel displays, thin-film photovoltaic cells and microcircuits — are at least four times higher than previously estimated, reports a new study published in the journal Geophysical Research Letters.

Using a technique that measures the prevalence of nitrogen trifluoride for the first time, researchers from the Scripps Institution of Oceanography found that the gas currently has a concentration of 0.454 parts-per-trillion (ppt) — up from 0.02 ppt in 1978 — and far higher than the previous estimate of 0.1 ppt for 2006. 0.454 ppt equates to 5,400 metric tons of nitrogen trifluoride in the atmosphere, an amount that has been increasing by 11 percent per year since 2006.

The finding is significant because nitrogen trifluoride is 17,000 times more potent than carbon dioxide as a greenhouse gas and survives in the atmosphere about five times longer. Therefore despite its minute (but increasing) use, the gas accounts for "about 0.04 percent of the total global warming effect contributed by current human-produced carbon dioxide emissions," according to a statement from the American Geophysical Union (AGU).

Scripps geoscientists Ray Weiss (green shirt) and Jens Muehle amid collection cylinders used to collect air samples from a variety of locations around the world. Weiss and Muehle led a study that found that the greenhouse gas nitrogen trifluoride, used in the manufacture of flat-panel monitors, escapes to the atmosphere at levels much higher than previously assumed.

"Nitrogen trifluoride is one of several gases used during the manufacture of liquid crystal flat-panel displays, thin-film photovoltaic cells and microcircuits," explained the AGU statement. "Many industries have used the gas in recent years as an alternative to perfluorocarbons, which are also potent greenhouse gases, because it was believed that no more than 2 percent of the nitrogen trifluoride used in these processes escaped into the atmosphere."

The authors say the results suggest that nitrogen trifluoride should be regulated as a greenhouse gas under international climate agreements.

"As is often the case in studying atmospheric emissions, this study shows a significant disagreement between 'bottom-up' emissions estimates and the actual emissions as determined by measuring their accumulation in the atmosphere," said lead author Ray Weiss of the Scripps Institution of Oceanography. "From a climate perspective, there is a need to add nitrogen trifluoride 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."

Weiss, R. F., J. Mühle, P. K. Salameh, and C. M. Harth (2008), Nitrogen trifluoride in the global atmosphere, Geophys. Res. Lett., doi:10.1029/2008GL035913, in press.

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