Letter▼ More on cutting auto greenhouse gases I write to point out a small error in the recent News Brief, “Cutting automotive greenhouse gas emissions” (Environ. Sci. Technol. 2003, 37, 9A). The brief mistakenly states that primary aluminum production, presumably using the Hall–Héroult Process or something similar, “requires a refining process using perfluorocarbons”. Although it is true that the Hall–Héroult Process does generate perfluorocarbons, it does not use them; rather, perfluorocarbons are incidentally generated by the reaction of the consumable carbon anodes with the molten electrolyte consisting of cryolite (Na3AlF6 (s) or 3NaF·AlF3 (s)), aluminum fluoride (AlF3 (s)), and calcium fluoride (CaF2 (s)), under steady-
© 2003 American Chemical Society
state operating conditions of about 950–980 °C, 100–150 kA, and 4.5 V. Notwithstanding this error, the brief had it right: Avoiding primary aluminum production via this recycling program is a good thing environmentally, as well as economically given that aluminum melts at about 660 °C. DAVID L. WAGGER Signum Environmental, Inc. Rockville, Md.
ES&T welcomes comments on articles in the A-pages. A letter to the editor can be sent to Managing Editor, Environmental Science & Technology, American Chemical Society, 1155 16th St., N.W., Washington, DC 20036; or by e-mail to
[email protected].
Correction The caption appearing with the graph (on page 440A) in the December 1, 2002, issue of ES&T in the news story “Wisconsin pulls out ahead on mercury controls”, incorrectly indicates that coal-fired power plants in Wisconsin would eventually emit approximately 38,000 pounds less of mercury annually if the state’s proposed mercury rule were finalized. The purpose of the chart is to show the amount of mercury that would accumulate in the environment over time under predicted yearly mercury emission rates. As such, the 38,000 pounds less of mercury does not refer to a per year basis but rather to the total amount of mercury that would accumulate during the 30-year period from 2002 to 2032.
MARCH 1, 2003 / ENVIRONMENTAL SCIENCE & TECHNOLOGY ■ 81 A
