By Janet Raloff
For weeks, the world has watched transfixed as televisions replay the Sept. 11 suicide plane crashes that destroyed the World Trade Center’s twin towers in New York. Soon after the fiery impacts, smoke plumes blanketed parts of lower Manhattan so heavily that survivors and rescuers at ground level experienced occasional blackout conditions on an otherwise sunny morning. Dense clouds continued to stream from the site as detritus burned steadily for more than a week.
Although the smoke originally came out black, it soon lost that sooty pall indicative of incomplete combustion. Explains Joseph M. Prospero of the University of Miami (Fla.), once the buildings started to burn, the combustion proceeded “fiercely but efficiently . . . so that the fuel burned relatively cleanly.”