Black carbon not so black
Black carbon, aka soot, may not have as big an effect on global warming as scientists had thought. Climate models generally assume that soot particles mix with other particles in the atmosphere in a way that enhances overall warming. Now, measurements of the air near Los Angeles, San Francisco and Sacramento suggest that instead of doubling this particular effect, black carbon increases it by an average of only 6 percent. Many simulations may thus overestimate warming attributable to black carbon — although soot contributes to atmospheric heating in other ways, as well as posing a major health threat. The work, led by Christopher Cappa of the University of California, Davis and Timothy Onasch of Boston College and Aerodyne Research in Billerica, Mass., appears in the Aug. 31 Science. —Alexandra Witze
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