A powerful greenhouse gas is at least four times more prevalent in the
atmosphere than previously estimated, according to a team of
researchers at Scripps Institution of Oceanography at UC San Diego.
Using new analytical techniques, a team led by Scripps geochemistry
professor Ray Weiss made the first atmospheric measurements of nitrogen
trifluoride (NF3), which is thousands of times more effective at
warming the atmosphere than an equal mass of carbon dioxide.
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.
generations of collection cylinders used to collect air samples from
locations around the world over the past 30 years. Scripps Institution
of Oceanography at UC San Diego geochemistry researchers Ray Weiss and
Jens 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.
"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. The research will be published
Oct. 31 in Geophysical Research Letters
, a journal of the American Geophysical Union (AGU).
Emissions of NF3 were thought to be so low that the gas was not
considered to be a significant potential contributor to global warming.
It was not covered by the Kyoto Protocol, the 1997 agreement to reduce
greenhouse gas emissions signed by 182 countries. The gas is 17,000
times more potent as a global warming agent than a similar mass of
carbon dioxide. It survives in the atmosphere about five times longer
than carbon dioxide. Current NF3 emissions, however, contribute only
about 0.04 percent of the total global warming effect contributed by
current human-produced carbon dioxide emissions.
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 2
percent of the NF3 used in these processes escaped into the atmosphere.
The Scripps team analyzed air samples gathered over the past 30 years,
working under the auspices of the NASA-funded Advanced Global
Atmospheric Gases Experiment (AGAGE) 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. Air samples are
collected at several stations around the world. The Scripps team
analyzed samples from coastal clean-air stations in California and
Tasmania for this research.
The researchers found concentrations of the gas rose from about 0.02
parts per trillion in 1978 to 0.454 parts per trillion in 2008. The
samples also showed significantly higher concentrations of NF3 in the
Northern Hemisphere than in the Southern Hemisphere, which the
researchers said is consistent with its use predominantly in Northern
Hemisphere countries. The current observed rate of increase of NF3 in
the atmosphere corresponds to emissions of about 16 percent of the
amount of the gas produced globally.
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.
In response to the growing use of
the gas and concerns that its emissions are not well known, scientists
have recently recommended adding it to the list of greenhouse gases
regulated by Kyoto.
"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," Weiss said. "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
"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," added Larry Smarr, director of the
California Institute for Telecommunications at UCSD, who was not
involved in the Scripps study.
Michael Prather is a UC 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."