The Most Potent Unknown Greenhouse Gas Revealed

The powerful greenhouse gas nitrogen trifluoride, NF3, is at least four times more widespread than scientists had believed, according to new research by a team at Scripps Institution of Oceanography at the University of California, San Diego.

Using new analytical techniques, a team led by Scripps geochemistry professor Ray Weiss made the first atmospheric measurements of nitrogen trifluoride, NF3.

"Accurately measuring small amounts of NF3 in air has proven to be a very difficult experimental problem, and we are very pleased to have succeeded in this effort," Weiss said Thursday, announcing the results of his team's research.

The research findings will be published October 31 in "Geophysical Research Letters," a journal of the American Geophysical Union.

Scripps geoscientists Ray Weiss, left, and Jens Muehle show cylinders used to collect air samples that they analyzed for concentrations of nitrogen trifluoride. (Photo courtesy Scripps Institution of Oceanography, UC San Diego)

The amount of the gas in the atmosphere, which could not be detected using previous techniques, had been estimated at less than 1,200 metric tons in 2006. The new research shows the actual amount was 4,200 metric tons.

In 2008, about 5,400 metric tons of the gas was in the atmosphere, a quantity that is increasing at about 11 percent per year.

This rate of increase means that about 16 percent of the amount of the gas produced globally is being emitted into the atmosphere, the researchers estimate.

Emissions of NF3 were thought to be so low that the gas was not considered to be a significant potential contributor to global warming.

Nitrogen trifluoride was not covered by the Kyoto Protocol, the 1997 agreement to reduce greenhouse gas emissions signed by 182 countries, although three other fluoride compounds are covered.

The protocol governs the emissions of carbon dioxide, methane, and nitrous oxide as well as other fluoride compounds - sulfur hexafluoride, hydrofluorocarbons, and perfluorocarbons.

In response to the growing use of the gas and concerns that its emissions are not well known, the scientists have recommended adding it to the list of greenhouse gases regulated by the protocol or its successor agreement now under negotiation.

"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.

Nitrogen trifluoride is one of several gases used during the manufacture of liquid crystal flat-panel displays, thin-film photovoltaic cells and microcircuits.

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 two percent of the NF3 used in these processes escaped into the atmosphere.

To obtain their information, the Scripps team analyzed air samples gathered in California and Tasmania over the past 30 years by the NASA-funded Advanced Global Atmospheric Gases Experiment network of ground-based stations.

The network was created in the 1970s in response to international concerns about chemicals depleting the ozone layer. It is supported by NASA as part of its congressional mandate to monitor ozone-depleting trace gases, many of which are also greenhouse gases.

The researchers found concentrations of NF3 rose from about 0.02 parts per trillion in 1978 to 0.454 parts per trillion in 2008.

Higher concentrations of NF3 were found in the Northern Hemisphere than in the Southern Hemisphere, which the researchers said is consistent with its greater use in Northern Hemisphere countries.

"This result reinforces the critical importance of basic research in determining the overall impact of the information technology industry on global climate change, which has already been estimated to be equal to that of the aviation industry," said Larry Smarr, director of the California Institute for Telecommunications at University of California, San Diego, who was not involved in the Scripps study.

Michael Prather is a University of California, Irvine atmospheric chemist who predicted earlier this year that based on the rapidly increasing use of NF3, larger amounts of the gas would be found in the atmosphere. Prather said the new Scripps study provides the confirmation needed to establish reporting requirements for production and use of the gas.

"I'd say case closed. It is now shown to be an important greenhouse gas," said Prather, who was not involved with the Scripps study. "Now we need to get hard numbers on how much is flowing through the system, from production to disposal."

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