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Ground Zero Air Pollution Unprecedented {Dr. Thomas Cahill, a University of California-Davis professor emeritus of physics and atmospheric sciences and a research professor in applied science, heads the UC Davis DELTA Group for Detection and Evaluation of Long-range Transport of Aerosols, a collaborative association of aerosol scientists at several universities and national laboratories. He presented these remarks February 23, 2002 at the Investigative Hearing of the National Ombudsman U.S. Environmental Protection Agency at New York City.} It became clear to our research group by about September 15 that the situation at the site of the World Trade Center collapse was unprecedented. Media reports and satellite observations showed that the heavy rains of September 14 and the hard work of the New York Fire Department had not prevented continuing massive emissions of a particularly bitter and acrid smoke.
Thus, when on September 28, 2001, Dr. Robert Leifer, of the Department of Energy's Environmental Measuring Laboratory in New York, called to ask if I could send one of our DELTA Group air samplers to his laboratory for analysis of the smoke, I naturally agreed. It was my understanding at the time that this was in support of local EPA efforts. I had worked with Bob for 15 years on aerosol studies and knew him to be expert in our continuously sampling rotating drum technology. Within five hours, we prepared a DRUM sampler, just back from NSF studies in Asia, and had it air expressed to Dr. Leifer. After Dr. Leifer sent the air samples back to us at UC Davis, our DELTA Group team and its resources - all volunteered - began analysis of the particles by size, time and composition. We used seven separate DELTA Group techniques at Davis and DOE's Lawrence Livermore and Lawrence Berkeley National Laboratories. We were pleased to find that we had a very high percentage of valid samples - more than 95 percent. Our studies are continuing, and we have released our early findings on particle mass from the samples collected October 2 through October 31 to the Department of Energy Environmental Measurements Laboratory on February 11. Additional data will be made available as soon as we complete our standard quality assurance protocols.
Our sampling site, at 201 Varick St., was roughly a mile north northeast of the collapse site. Regional meteorology from NOAA's HYSPLIT trajectory model identified periods when smoke and dust could have been blown to the site. On a few occasions, the smoke plume blew directly to the sampling site. In a number of ways our findings support EPA results on particles of the size PM-10 and PM-2.5 and on lead, with our 24-hour averaged results generally somewhat less than those seen by the EPA at its sampling sites closer to the collapse site. When the wind was clearly blowing away from the collapse site, mass levels at our site were generally low. However, our highly time and size resolved mass data from the Center for Accelerator Mass Spectroscopy at Lawrence Livermore National Laboratory, which includes over 7,000 measurements with time resolution under an hour in many cases, showed that the average data included very intense peaks of short duration, a few hours in length. In addition, our size-resolved mass data indicated that the sizes of particles appearing at our site were both in high concentration and very fine, unlike any we had ever sampled before. One particular period on October 3 had unprecedented levels of mass and very fine particles, decreasing on subsequent days. Until we have more local information, however, we cannot determine whether there were increased emissions from the collapse site on that day, or whether the intense plume represented typical conditions that just happened to impact the Varick Street site during those few hours. This finding of high levels of very small particles led us to release our data on February 11, in hopes that the information could help focus and direct cleaning and re-entry activities in New York City near the collapse site. In this regard, we strongly support the first recommendation of the NYC Department of Health on extensive use of water in cleanup activities, and we would include fabrics and rugs. By composition and morphology, the coarse particles are consistent with finely ground concrete, drywall and powdered glass in rounded, not shard-like, modes. We found only a few asbestos fibers. The coarse particles had dark coloring, which would normally be associated with a coating of soot.
We plan to do much more analysis on the nature and amount of these coatings. The presence of coarse particles immediately after days of rain indicated that they were being continually re-generated from a dry, hot source, not re-suspended from roadways and other surfaces. The mass of particles in the very fine mode on October 3, in particular, at our sampling site was by far the highest we have ever seen or seen published. It exceeded levels recorded during the oil fires in Kuwait and in downtown Beijing during the coal heating season. The very fine particles were high in a number of species generally associated with combustion of fuel oil - such as sulfur, vanadium, and nickel, and incineration of plastics and other organic matter. There was also an unusual, very fine, silicon-containing aerosol. This latter type of aerosol can be produced only by very high temperatures, including vaporization of soil and glass. We had seen this previously, but at much lower concentrations, in the plumes of coal-fired power plants in the EPA BRAVO study in Texas, the burning oil fields of Kuwait, and Beijing during the winter coal heating season. In the case of metals, we saw many different species in the very fine particles. Most, including lead and mercury, were at low concentrations at our site, but some, such as vanadium, were the highest that we have seen recorded. We recorded other aerosol plumes at the sampling site through the rest of October, though none reached the levels of October 3. The very fine silicon, in particular, decreased steadily and was absent in the last week of October, while sulfur-containing particles and the vanadium and nickel continued to be seen. A direct plume that hit the site on October 24, based on National Oceanic and Atmospheric Administration records, was far smaller than the October 3 impact, with almost no very fine silicon seen. The additional measurements we are now making include a large number of pictures by scanning electron microscopy; organic speciation by laser desorption ionization time-of-flight mass spectrometry; detailed surface chemistry of the coarse particles by synchrotron x-ray fluorescence at the Advanced Light Source; and optical spectrometry at Davis in the 320 nanometers to 820 nanometers range.
Standard quality assurance protocols require re-analysis of samples prior to data release, and thus is scheduled at the ALS in early March, after which we will provide additional compositional data to Department of Energy and EPA. There also would be great value in analyzing the remaining samples from November 1 through mid-December to help put the early October results into perspective. I would like to gratefully acknowledge the key role of Dr. Robert Leifer, DOE EML, without whose initiative this study would never have occurred and without whom we could never have acquired such a high percentage of valid air samples. I would like to gratefully acknowledge the contributions of my colleagues in the DELTA Group, including Professor Jim Shackelford (morphology), Professor Pete Kelly (organics), Dr. Steve Cliff (Head, S-XRF ALS PRT), all of UC Davis; Professor Kevin Perry, Meteorology, University of Utah (S-XRF data reduction); Dr. Graham Bench, Dr. Patrick Grant and Dawn Ueda (mass by STIM, hydrogen by PESA, CAMS, LLNL); Mr. Michael Jimenez-Cruz (DELTA laboratory and field manager); Professor Cathy Cahill (Chemistry, University of Alaska, NOAA HYSPLIT); and the DELTA staff: Lee Portnoff (beta mass), Jeanette Martin (communications and administration), Victor Rey (samplers), and Dr. Roger Miller (optics). Finally, I would like to acknowledge all those persons and agencies that helped develop our technology, too numerous to name in detail, but including the National Science Foundation under contract ATM 0080225, the EPA under a BRAVO subcontract, the National Park Service and IMPROVE, especially Dr. Bill Malm, and NOAA CMDL at Boulder, especially Dr. Russ Schnell. Our results and conclusions are ours alone, however, and are not sanctioned by any of the agencies or persons named above. Links: For details of the technology used by the DELTA research team, visit: http://delta.ucdavis.edu, which lists many collaborators and provides descriptions and publications. Help for those affected by the terrorist attacks is available through the 9/11 United Services Group . Find out about the Exhibition and Public Programs to Commemorate September 11 at the Library of Congress. The 9/11 Memorial Quilt Project is touring. Find out where it is at: http://unitedinmemory.net/uimz/participate.htm Suzanne Vega and the Greenwich Village Songwriters Exchange Vigil CD is online at: http://www.vigilcd.org/ |
Dr. Thomas Cahill (Photos courtesy 
Thomas Cahill explains to reporters what is in the Lower Manhattan air near Ground Zero.
Firefighters battle smouldering fires and sift through the wreckage of the World Trade Center, September 13, 2001. (Photo by Andrea Booher courtesy 
Aerial view of Ground Zero, September 29, 2001 (Photo by Michael Reiger courtesy 