Researchers at Scripps Institution of Oceanography, UC San Diego, and colleagues used high-precision measurements of atmospheric gases to find that two potent perfluorocarbon greenhouse gases are emitted to the atmosphere from aluminum and semiconductor manufacturing in far greater quantities than these industries had estimated.
An earlier study found that the reported emissions of these perfluorocarbons, which are among the compounds regulated under the United Nations Framework Convention on Climate Change (UNFCCC), only accounted for half of the emissions observed in the atmosphere during the period 2002-2010. This study distinguishes these emissions by type of industry to further understand the sources of this discrepancy.
Because of the relative scarcity of these human-made compounds, their total warming effect is still only 0.3 percent of that of carbon dioxide (CO2), but co-author Ray Weiss, a distinguished professor of geochemistry at Scripps, said the finding supports maintaining international treaties regulating greenhouse gas emissions. That is especially true given ongoing worldwide demand for products from both industries and the acceleration of aluminum production in some countries including China, which is not required to report emissions from either industry to the UNFCCC.
“The reason to regulate these emissions has to do with their growth potential,” Weiss said.
The cause for concern lies in the fact that any emissions of these perfluorocarbons into the atmosphere are likely to stay in the atmosphere for the foreseeable future. Tetrafluoromethane and hexafluoroethane, the two major perfluorocarbons in the atmosphere, last 50,000 and 10,000 years, repectively, before breaking down. This extreme stability leads to significantly higher capability in trapping heat in the atmosphere -- these two compounds are respectively 6,630 and 11,100 times more effective by mass in this regard than CO2.
The study, “Quantifying aluminum and semiconductor industry perfluorocarbon emissions from atmospheric measurements,” appeared July 16 in the journal Geophysical Research Letters, published by the American Geophysical Union. Its authors said the main accomplishment of the work is the ability it provides to discriminate between the emissions of two large industries. Being able to quantify which emissions come from which industry holds both accountable, and helps point to specific areas where the industry estimates can be improved.
The study draws on data collected by the Advanced Global Atmospheric Gases Experiment, or AGAGE, a program launched in 1978 that measures trace gases in the atmosphere at nine locations around the world. The researchers focused on perfluorocarbon readings made at stations in Australia and Korea, the locations of which are downwind from aluminum and semiconductor manufacturing locations. At present, 40 percent of the world’s aluminum is produced in China, emissions from which appear in data from Korea.
Perfluorocarbons exist in air only at concentrations of parts per trillion, but the researchers were able to distinguish the emission sources based on the ratio of tetrafluoromethane against hexafluoroethane.
“The International Aluminium Institute has been very receptive to our work,” said lead author Jooil Kim, a postdoctoral researcher in Weiss’ lab. “They acknowledge that China is a big uncertainty at this point, and research in industry and in academia is continuing to better understand the emissions from aluminum production.”
Unfortunately, said the researchers, the semiconductor industry regards its uses of perfluorocarbon gases as proprietary information associated with proprietary manufacturing processes, and so has been less forthcoming regarding their emissions of specific perfluorocarbon compounds.
Besides Weiss and Kim, study co-authors include Jens Mühle, Tim Arnold, Christina Harth, and Peter Salameh of Scripps Oceanography; Paul Fraser, Paul Krummel, and L. Paul Steele of the Commonwealth Scientific and Industrial Research Organization in Australia; Shanlan Li and Sunyoung Park of Kyungpook National University in Sangju, South Korea; Anita Ganesan and Ron Prinn of Massachusetts Institute of Technology; Seung-Kyu Kim of Incheon National University in Incheon, South Korea; Mi-Kyung Park and Kyung-Ryul Kim of Seoul National University, Seoul, South Korea and Institute of Science and Technology, Gwangju, South Korea.
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