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Sulfur hexafluoride emissions Dear Editor: In her article, K. Betts {Environ. Scii Technoll.1998 32(21), 487A-488A) reported ongoing research on the emissions of sulfur hexafluoride (SF6), which is notorious for its extraordinary environmental stability and its relative strength as a greenhouse gas. Maiss and Brenninkmeijer {Environ. Scii Technol. 1998, 32(20)) 3077-3086) (hereafter MB) recently resolved the discrepancy between the observed accumulation rate of SF in the atmosphere and attributable emissions. Thcv bciscd their analysis on industry oil r u p v
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of SF sales into different applications yet they still postulated a major unidentified source in North America In this note we suggest that MB overestimated North American sources and underestimated Asian emissions well as emissions associated with the testing installation and use of gas insulatpH switchgear which are
widely used by electrical utilities. MB proposed North American to the journal's home page emissions as the source of the discrepancy based on regional sales when it has completed estimates provided by two Eurorigorous peer-review, editing, pean SF6 manufacturers. Their information may therefore be rather and is fully approved for imprecise outside of Europe. MB's publication. own data provide clues that SF6 Articles ASAP are published emissions from Asia may be underestimated. In their paper, they reanywhere from 2 weeks to port that about 3500 tons of SF6 are almost 3 months before they installed in North American gasinsulated switchgear as compared appear in print, and carry all to 4500 tons in Europe and the electronic enhancements 18 000 tons in the rest of the world Japan reports a production of that put Web Editions at the 2400 tons of SF in 1995 excluding head of the class for gas that was exported in electrical equipment This alone corresponds flexibility and functionality. to 32% of reported worldwide sales Articles ASAP- one more way Considering the economic growth prevailing in Southeast Asia in the to Know It Now with ACS mid-1990s we suggest that most of Web Editions. For more the 1700 tons of SF sold which MB could not allocate, were used in information, visit the ACS Southeast Asia rather than in North Publications website, America. MB speculated that possibly sigpubs.acs.org nificant emissions occur from the use of SF6 in accelerators. Worldwide, less than 1000 tons of SF6 are ACS PUBLICATIONS banked in accelerators (private communication National Electrostatics Corporation, 1998). Even im5 6 A • FEB. 1, 1999 / ENVIRONMENTAL SCIENCE & TECHNOLOGY / NEWS journals, each article is posted
plausibly high leakage rates—of 10% per year—would not contribute significantly to global SF6 emissions, which MB found to be 6100 tons in 1995. MB also proposed that SF6 emissions associated with the production of magnesium might be strongly underestimated and thus account for the missing source. We are inclined to reject this proposal because the 20% decrease of world magnesium production in the years 1992-1994 remains undetectable in the atmospheric data. We suggest the following alternative picture of global emissions of SF6: The electrical sector is responsible for more than 80% of global emissions. Roughly one-third of the SF6 sold to manufacturers and users of gas-insulated switchgear is banked in new equipment. Leakage from gas-insulated switchgear probably contributes far less than 10% to global emissions. Most SF6 emissions apparently occur during the design and testing, shipping, installation, repair and maintenance, and the decommissioning of gas-insulated switchgear As K Betts emphasized in her article, it is technically feasible to avoid most of the SF emissions from the electrical sector A considerable gap thus exists between best and common practice of SF use 6
JOCHEN HARNISCH RONALD G. PRINN Joint Program on the Science and Policy of Global Change Massachusetts Institute of Technology 77 Massachusetts Ave., Bldg. E40-270 Cambridge, MA 02139
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