Where's the smoke from the N.Y. fires?

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."

Within hours of the crashes, federal scientists began tracking the smoke with satellites as well as air-monitoring stations that they set up around the former World Trade Center.

Overhead imaging showed that for the first day or so, the smoke plume diffused over New Jersey, Prospero observes. From then on, it mostly blew out to sea, says Bruce Hicks, director of the National Oceanic and Atmospheric Administration's Air Resources Laboratory in Silver Spring, Md. The smoke "maintained an almost constant distance offshore as it moved down New Jersey and Delaware," he notes. It then dissipated rapidly, raining out into the ocean.

This suggests that any major respiratory health risks would probably come from inhaling smoke at or near the fires. Federal air monitoring for lead, asbestos, and volatile organic compounds on Sept. 11 found that these were either "not detectable or not of concern," according to an Environmental Protection Agency report. Sampling of ambient air quality and dust concentrations in lower Manhattan and Brooklyn the next day concluded that both "were uniformly acceptable."

Although EPA scientists are continuing to monitor air quality on and around the site, the agency reports that pollution from the fires "is unlikely to cause significant health effects"--particularly if those at ground zero, such as tire fighters, don protective gear. EPA has helped other agencies procure and distribute such gear to rescue-recovery crews at the World Trade Center site and the Pentagon in Washington, D.C., the site of another fiery suicide crash.