Remarks by Thomas A. Cahill, Ph.D.

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 5 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 7 separate DELTA Group techniques at Davis and DOE's Lawrence Livermore and Lawrence Berkeley National Laboratories. (For details of the technology, see our web site http://delta.ucdavis.edu, listing our many collaborators and providing descriptions and publications.) 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 DOE EML on February 11. Additional data will be made available as soon as we complete our standard quality assurance protocols, with the next major release of information expected in mid-March.

Our sampling site, at 201 Varick St., was roughly a mile north north-east 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 can not 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 NOAA 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 DOE 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 Prof. Jim Shackelford (morphology), Prof. Pete Kelly (organics), Dr. Steve Cliff (Head, S-XRF ALS PRT), all of UC Davis; Prof. 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); Prof. 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.

Thomas A. Cahill, Ph.D.
University of California, Davis

One Shields Avenue
Davis, California 95616
Phone: (530) 752-1120

 

Research Activities

Thomas A. Cahill, Ph.D., is a Professor Emeritus of Physics and Atmospheric Sciences at the University of California, Davis, and a Visiting Professor of Applied Science. He has pioneered studies of fine particles in the atmosphere (atmospheric aerosols) by continuous, size-resolved sampling and compositional analysis since 1970.

He is the co-developer and long-time principal investigator of programs in air quality and visibility in U.S. national parks and monuments, 1977-1997. His past studies include collection and analysis of aerosols from the eruption of Mount St. Helens, Oregon; Arctic haze from Siberia; dust from Africa and Asia; and the Gulf War oil fires of 1991. In 1997, Dr. Cahill formed the DELTA Group (Detection and Evaluation of Long-range Transport of Aerosols) to bring new technology to aerosol analysis and to address the growing concern about aerosol impacts and climate change.

Dr. Cahill is presently the principal investigator of a large NSF Atmospheric Sciences study of aerosols from Asia. The DELTA Group is also currently involved in numerous other studies, including EPA-funded analysis of aerosols in Big Bend National Park, Texas; California Air Resources Board studies of aerosols in California; studies of diesel particles from current and new clean diesel technology; aerosol transport across the Atlantic; and air quality at Lake Tahoe and other Western and Midwestern sites.

Dr. Cahill was named Scientist Volunteer of the Year in 2001 by the California Chapter of the American Lung Association for his studies of fine particles and death in California.