Study Says Ground Zero Soot Lingered
By Kirk Johnson, New York Times, September 11, 2003

New research into the impact of air pollution from the World Trade Center disaster mostly confirms, for better and for worse, some of the earliest tentative conclusions reached just after the attack, scientists said yesterday. The air across most of Lower Manhattan quickly returned to generally normal conditions, with periodic jumps in the levels of ash and soot, but remained downright horrible for weeks at the smoldering mound of ground zero itself.

What emerged at a daylong conference in Manhattan sponsored by the American Chemical Society were the nuances of that analysis. Scientists studying the smoke from ground zero said that the mixture in many cases was simply beyond human experience. One compound, for example, called 1,3-diphenyl propane — apparently forged by the intense pressure and heat of the fires and collapse — had never been seen by scientists and has been adopted as a kind of signature trace element of the disaster.

But at the same time, the new research underscored how quickly the smoke and its elements dissipated into the atmosphere. The plume was so hot from the intense fires, which smoldered for three months after the attacks, that only sporadically, scientists said, did it touch down anywhere beyond ground zero. Hot air rises, and it went up fast.

What that presents, the scientists said, is a kind of good-news-bad-news formulation. Many ground zero workers and volunteers who labored without respirators — a common sight in the early weeks of rescue and recovery — were exposed to a chemical stew that was probably worse, and certainly more complex in its elements, than previously imagined. And most residents and workers downtown — while they may well have suffered from the dust at the collapse and periodic wafts from the smoke plume — were largely spared the prolonged exposure that usually raised the greatest health concerns.

"The concerns have become more and more focused on ground zero," said Thomas Cahill, a professor emeritus of physics and atmospheric science at the University of California at Davis. Dr. Cahill said that the conclusions from his work — testing the air for most minute particles that can penetrate deeply into lungs — along with other presentations about the track of the plume, presents a picture that is both alarming and reassuring.

"The stuff we saw in those plumes was truly nasty," he said. "But most of the time the plume rose," and so had only localized effects.

The division between ground zero and the rest of Lower Manhattan has been at the heart of the two-year scientific debate about the disaster's environmental effects.

Some scientists said yesterday that the new research underlined more than ever the degree to which rescue workers and volunteers at the disaster site itself were put at risk, either because wearing lung protection was not always strictly enforced or because the respirators themselves were not well suited to the job.

What people were told, both in and out of ground zero, has also become a political issue, since the inspector general of the federal Environmental Protection Agency concluded last month that the agency's former administrator, Christie Whitman, had lacked adequate scientific evidence when she reassured the public on Sept. 18, 2001, that the air downtown was "safe to breathe." Mrs. Whitman has said that the science at the time supported her statement.

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