The missing greenhouse gas
Flat-screen TV manufacturing emits chemical with warming effect
An unregulated chemical used to make flat-screen televisions and computers has 17,000 times the climate-warming effect of carbon dioxide, say UC Irvine Earth system scientists Michael Prather and Juno Hsu. Their assessment of nitrogen trifluoride, or NF3, in a recent issue of Geophysical Research Letters caught the attention of global warming experts and journalists worldwide, with news stories appearing in the Los Angeles Times,Discover, New Scientist, Chemistry World and on National Public Radio.
Prather, Fred Kavli Chair and director of the UCI Environment Institute, discusses NF3 and why it is such a global warming threat:
Q: What is NF3 and how does it react in the atmosphere?
A: NF3 is a man-made gas that – once released into the atmosphere – circulates from the surface to the stratosphere hundreds of times before it is destroyed by solar ultraviolet radiation. The average lifetime of an NF3 molecule in the atmosphere is 550 years. NF3 is nearly chemically inert in the atmosphere, but it is very effective in absorbing the infrared radiation that the Earth emits. By trapping this infrared radiation, NF3 becomes a potent greenhouse gas. In terms of kilograms emitted, NF3 is about 17,000 times more effective as a greenhouse gas than carbon dioxide.
Q: How is NF3 used to make flat-screen televisions and computers?
A: When hit with microwave discharge or a plasma beam, NF3 releases fluorine atoms that are used to clean the chamber in which flat-screen liquid crystal display panels are made. It also can be used to release fluorine to etch and cut the silicon substrate for computer chips. As I understand it, NF3 is used in large volumes in the LCD screen process.
Q: Why do you consider NF3 the “missing greenhouse gas”?
A: NF3 is not included in the Kyoto Protocol list of greenhouse gases. This fact is perhaps an oddity. NF3, like many synthetic greenhouse gases, was not recognized specifically as a major industrial gas in 1995 when the United Nations’ Intergovernmental Panel on Climate Change report listed the global warming potentials of many greenhouse gases. The rapid rise in production by the chemical industry had gone almost unnoticed.
Q: Is UCI measuring NF3, and if so, how?
A: The labs of Eric Saltzman and Murat Aydin in Earth system science are preparing to measure the atmospheric abundance of NF3. It is an extremely slippery molecule. There are probably only three laboratories in the world with the experience of measuring gases like NF3, and UCI has one of them.
Q: How should industry address the NF3 issue?
A: The major NF3 producer, Air Products and Chemicals, Inc., says that 98 percent of the gas is destroyed during the manufacturing process, and thus NF3 is an environmentally safe gas. However, there should be no doubt that NF3 is a highly hazardous gas in terms of global warming. We have no reliable estimates about leakage during production, shipping and decommission. This gas is extremely volatile and difficult to measure at low abundances, so we cannot be sure that industry estimates or measurements are accurate.
Q: What can the general public do about NF3?
A: The public should recognize that technology has a price and that the manufacture of these screens is not greenhouse-free. NF3 is not special; it is one of many high-tech products that potentially can have a large carbon footprint. The public should demand that the carbon footprint of such products be evaluated independently (not by the chemical manufacturers) and disclosed as energy efficiency is posted on appliances.