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Roger Clark, the astrophysicist who heads the US Geological Survey (USGS)‘s portion of the AVIRIS program in Denver, contacts Robert Green, head of the AVIRIS program at NASA’s Jet Propulsion Laboratory in Pasadena. (The AVIRIS, or Airborne Visible Infrared Spectrometer, is a remote-sensing unit used by NASA to determine the chemical composition of a planet’s surface and atmosphere by analyzing the infrared signatures of minerals that are reflected from the ground and comparing them with the unique peaks and curves of the signatures of thousands of minerals and materials in the USGS database. (Schneider 2/10/2002) AVIRIS has been used before to scan Superfund toxic sites to map hot spots of harmful substances.) (Revkin 9/17/2002) He asks Green for NASA permission to use the AVIRIS over New York City and parts of New Jersey to determine the chemical composition of the dust and debris resulting from the collapse of the World Trade Center. (Schneider 2/10/2002) NASA gives the go-ahead on September 13 (see September 13, 2001).
Robert Green, head of the AVIRIS program at NASA’s Jet Propulsion Laboratory in Pasadena, informs Roger Clark, the astrophysicist who heads the US Geological Survey (USGS)‘s portion of the AVIRIS program in Denver, that NASA will permit the USGS team to use AVIRIS in an attempt to determine the chemical composition of the dust and debris that resulted from the collapse of the World Trade Center (see September 12, 2001). The crew will mount the unit to a de Havilland Twin Otter prop plane owned by NASA, which will make several passes over the WTC and surrounding area. “The Federal Emergency Management Agency and the White House Office of Science and Technology Policy… signed off on the flight. And the Air Force [has] agreed not to shoot the Twin Otter down,” the St. Louis Post-Dispatch will later report. (Schneider 2/10/2002)
US Geological Survey (USGS) geophysicists Gregg Swayze and Todd Hoefen fly to New York City to get calibration data from the ground that will supplement the data collected by AVIRIS (see 12:00 p.m. September 16, 2001-2:00 a.m. September 17, 2001). They collect 35 dust samples from a variety of locations around Ground Zero including window ledges, flower pots and car windshields. While “AVIRIS offers a bird’s-eye view…,” Roger Clark, a USGS astrophysicist, later explains to the St. Louis Post-Dispatch, “The ground samples… gave us up-close, specific information on specific points.” On September 19 they send their data to the USGS office in Denver over the Internet. The next day, scientists will begin conducting a variety of tests on the samples (see September 20, 2001). (Schneider 2/10/2002; Schneider 2/10/2002)
US Geological Survey (USGS) scientists begin performing tests on the dust samples collected by USGS geophysicists, Gregg Swayze and Todd Hoefen, during the previous three days (see September 17, 2001-September 19, 2001-). Roger Clark (the astrophysicist who heads the AVIRIS program at USGS), Gregg Swayze, Todd Hoefen and Eric Livo (another USGS scientist) analyze samples in the Imaging Spectroscopy Lab and Gregory Meeker (head of the USGS’s microbeam laboratory) views samples with the scanning electron microscope and conducts energy dispersive spectroscopy. Other USGS scientists study the samples using X-ray diffraction, X-ray fluorescence, as well as chemical analysis and chemical leach testing. Within hours, the results from the various tests indicate the presence of asbestos and an “alphabet soup of heavy metals.” Each of the different techniques used to determine the chemical components of the dust “back each other up,” Swayze later explains to the St. Louis Post-Dispatch. “Some techniques can see more than others, and we were throwing in every technique we had in house,” he says. Tests revealed the dust to be extremely alkaline with a pH of 12.1 (out of 14). (Schneider 2/10/2002) and that some of it was as caustic as liquid drain cleaner. (Schneider 2/10/2002) “We were startled at the pH level we were finding,” Swayze adds. “We knew that the cement dust was caustic, but we were getting pH readings of 12 and higher. It was obvious that precautions had to be taken to protect the workers and people returning to their homes from the dust.” Sam Vance, an environmental scientist with the EPA, sends the results to officials at the EPA, the New York health department and US Public Health Service. (Schneider 2/10/2002)
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