Air near the collapsed World Trade Centers contained unprecedented amounts of tiny particles a month after the Sept. 11, 2001, terrorist attacks, according to University of California, Davis, researchers.

"The air from ground zero was laden with extremely high amounts of very small particles, probably associated with high temperatures in the underground debris pile," says Thomas A. Cahill, a UC Davis professor emeritus of physics and atmospheric science. Very fine particles of air pollution are defined as between 0.09 and 0.24 µm in size. They can travel deeper into the lungs than do coarse particles, which get filtered by the nose or coughed out of the throat and upper lungs.

Very fine particles collected near ground zero in October 2001 contained high levels of sulfur and sulfur-based compounds, primarily sulfuric acid, all of which can irritate lung tissue, the Detection & Evaluation of Long-range Transport of Aerosols (DELTA) Group at UC Davis found. Silicon, likely from the tons of glass in the debris, also made up a high percentage of the fine particulates. High concentrations of very fine bits of iron, titanium, vanadium, nickel, copper, and zinc were also found. The analysis found few asbestos fibers.

The highest concentration of very fine particles found by the DELTA Group was 58 µg per m³. Concentrations of very fine particulates airborne near ground zero decreased sharply during October 2001.

According to Cahill, head of the DELTA Group, "Even on the worst air days in Beijing, downwind from coal-fired power plants, or in the Kuwait oil fires, we did not see these levels of very fine particulates."

The DELTA Group's data are available at http://delta.ucdavis.edu/WTC.htm.

DUSTY While air particulate concentrations decreased sharply overall during October, clouds of dust were still being released during cleanup operations.

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