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Air Today . . . Gone Tomorrow Article
Trade
Center Air Held Unprecedented Amounts of Very Fine Particles, Silicon, Sulfates, Metals,
Say UC Davis Scientists
UC Davis News and Information,
February 11, 2002
In the most thorough analysis yet of the dust and smoke blown through
lower Manhattan after the collapse of the World Trade Center, researchers at the
University of California, Davis, today described unprecedented clouds of very fine
particles that should be considered in evaluating rescue workers' and residents' health
problems.
Based on their findings, the UC Davis researchers also recommended
specific cleaning methods for contaminated apartments, offices, schools and other indoor
spaces. "No one has ever reported a situation like the one we see in the World Trade
Center samples," said UC Davis researcher Thomas Cahill, Ph.D., an international
authority on the constituents and transport of airborne particles. "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. Normally, in New York
City and in most of the world, situations like this just don't exist."
Cahill, a UC 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. The DELTA Group
has made detailed studies of aerosols from the 1991 Gulf War oil fires, volcanic
eruptions, global dust storms, and most recently Asia.
The Manhattan air samples were collected at the request of a U.S.
Department of Energy scientist from Oct. 2 through mid-December, by a DELTA Group air
monitor placed on a rooftop at 201 Varick St., one mile north-northeast of the trade
center complex.
The samples were collected continuously in eight separate size modes
from coarse (12 micrometers diameter) to ultra-fine (0.09 micrometers diameter). Regional
meteorology showed that the site at Varick Street could have received material from the
World Trade Center site about half the time.
The samples were periodically shipped back to Davis, where the DELTA
Group analyzed the samples for size, shape and composition. They used a suite of seven
techniques including synchrotron-induced X-ray fluorescence (at DOE's Advanced Light
Source at Lawrence Berkeley Laboratory), scanning transmission ion microscopy and proton
elastic scattering analysis (at DOE's Lawrence Livermore National Laboratory), and soft
beta mass measurements and scanning electron microscopy (at UC Davis).
"The UC Davis DELTA Group's ability to measure and analyze
particle size, composition and time continuously, day and night, is unequaled,"
Cahill said.
All analyses were done on a volunteer basis and will be available as
public documents. We report today on the data from Oct. 2 through Oct. 31, 2001.Airborne particles
and human health
In
general, there are myriad ways that materials released into the air can affect human
health. What the particles are made of matters; so do size, shape and quantity.
The DELTA team analyzed the samples for the unique chemical and
physical signatures of dozens of substances, including elements from concrete and glass,
such as silicon; from burning fuel oil, such as sulfur, vanadium and nickel; and from
burning computers and electrical systems, such as lead. They also looked for organic, or
carbon-based, compounds from burning wood, plastic and carpets. And they tested for glass
shards and asbestos.
Some of these materials are known to cause health problems in some
people when they are inhaled in sufficient amounts. Sulfur, for example, can irritate lung
tissues. Lead can damage the central nervous system. Some carbon-based compounds can cause
cancer. So can the mineral asbestos.
Just as the composition of inhaled particles can affect health, so can
size. The team analyzed the particles by size in eight ranges from coarse (12 micrometers
to 5 micrometers in diameter) to very fine (0.24 micrometers to 0.09 micrometers in
diameter). Most of the ultrafine mode (particles less than 0.1 micrometers) was not
collected.
Coarse particles are typically filtered by the nose or coughed out of
the throat and upper lungs. They can irritate the mucous membranes, causing coughs and
nosebleeds. In some individuals, they can cause allergic reactions such as dry eyes; nose,
throat and skin irritation; coughing, sneezing and respiratory distress. They can also
cause breathing problems or aggravate pre-existing breathing problems, such as asthma.
However, very fine particles can travel deep into human lungs. Such
small particles may have no immediate apparent health effects in moderate concentrations,
but they typically are removed from the lungs through the bloodstream and heart,
increasing the possibility of health impacts.
There are no established safe limits for inhaled very fine particles.
The closest reference is the U.S. EPA "PM2.5" standard, which limits the
allowable mass of airborne particles in the size range 2.5 micrometers to 0 micrometers.
That standard is based on health studies of typical air samples, in which very fine
particles are a small fraction of the total mass.
In contrast, in the World Trade Center samples analyzed at UC Davis,
the very fine particles are a large fraction of the total mass.
In a news conference today, the DELTA researchers described key
findings in these categories: very fine particles, coarse particles, metals, asbestos and
glass.
Very fine particles
There were
numerous events when bursts of wind lasting six to eight hours carried unprecedented
amounts of very fine particles to the sampling site. In the largest spike, the DELTA Group
analysis found 58 micrograms per cubic meter of very fine particles in one 45-minute
period -- "an extremely high peak," Cahill said.
Cahill said the very fine particles contained high levels of sulfur and
sulfur-based compounds, which in early analyses appear to have been dominated by sulfuric
acid. The very fine particles also contain high levels of very fine silicon, potentially
from the thousands of tons of glass in the debris.
Cahill noted that even those large amounts were likely to be smaller
than those present at Ground Zero and some other parts of Lower Manhattan, since weather
data show that typically only part of the dust clouds traveled directly over the sampling
site.
"Even on the worst air days in Beijing, downwind from coal-fired
power plants, or in the Kuwaiti oil fires, we did not see these levels of very fine
particulates," Cahill said. The amounts of very fine particles, particularly very
fine silicon, decreased sharply during the month of October.
Coarse particles
Similar to
the high concentrations of very fine particles, virtually all the air samples from the
trade center site carried high concentrations of coarse particles -- those about 12
micrometers to 5 micrometers in diameter.
"These particles simply should not be there," Cahill said.
"It had rained, sometimes heavily, on six days in the prior three weeks. That rain
should have settled these coarse particles." The finding suggests that coarse
particles were being continually generated from the hot debris pile. This observation is
at least qualitatively supported, for while they are still being analyzed, the coarse
particles appear to be coated with combustion products, including soot, Cahill said.
Metals
Many
different metals were found in the samples of very fine particles, and some were found at
the highest levels ever recorded in air in the United States. However, there are few
established safety guidelines for airborne metals. One metal for which there is a
guideline, lead, was present at low levels in fine and very fine particles.
Some of the metals for which there are no guidelines that were present
in very fine particles in relatively high concentrations were iron, titanium (some
associated with powdered concrete), vanadium and nickel (often associated with fuel-oil
combustion), copper and zinc. Mercury was seen occasionally in fine particles but at low
concentrations. Many of those metals are widely used in building construction, wiring and
plumbing. Some are common in computers. The metal content of the coarse particles is still
being analyzed.
Asbestos and glass
Although
some asbestos was used in the buildings for fireproofing and in floor tiles, and the DELTA
group checked for it carefully using the electron microscope, they found very few asbestos
fibers, even in the very fine particles.
Some particles that appeared to be glass were seen, but they were not
in the form of long shards, which can mimic asbestos fibers.
Clean-up
recommendations
All
evidence indicates that ambient air in New York City now is little influenced by the World
Trade Center collapse, especially since the fires are out and the debris pile has cooled.
However, the presence of large amounts of very fine particles as late as October means
that indoor clean up should be done carefully, Cahill said. Very fine particles will have
penetrated crevices and fabrics in a way normal dust doesn't. And they are easily
re-suspended, which re-exposes the room's occupants to them.
Cahill strongly supports the recommendations made by the New York
Department of Health regarding washing with water, and said:
-- Don't use vacuum cleaners or brooms because they re-suspend particles. Do use wet rags,
mops and wet-vacuum-type cleaners.
-- Wipe all surfaces, including window blinds, picture tops and door frames, with wet
rags.
-- Drapes and curtains should be washed or dry-cleaned. Furniture fabrics should be
steam-cleaned. Carpets should be wet-cleaned.
-- Use high efficiency electrostatic or HEPA air filters in furnaces and air conditioners.
-- Keep humidity reasonably high indoors, to keep very fine particles from floating
around.
UC Davis DELTA
Group
The
UC Davis DELTA Group is one of the world's leading research groups in analyzing the size,
composition and movement of airborne particles. DELTA Group scientists analyzing the trade
center samples included Cahill; engineering professor James Shackelford, Ph.D., who led
the scanning electron microscopy; chemistry professor Peter Kelly, Ph.D. who led the mass
spectroscopy; assistant research engineer Steve Cliff, Ph.D., who is project manager for
the synchrotron program, and laboratory and field manager Michael Jimenez-Cruz,
toxicologist.
Key collaborators from other institutions were Kevin Perry, Ph.D., a
former Cahill postdoctoral collaborator and now an assistant professor of meteorology at
the University of Utah, Salt Lake City; Graham Bench, Ph.D., a project investigator at the
Center for Accelerator Mass Spectroscopy, U.S. Department of Energy's Lawrence Livermore
National Laboratory, and his team of scientists; and Jodye Selco, Ph.D., a visiting
professor at UC Davis and a professor of chemistry at the University of Redlands,
Redlands, California.
The DELTA Group's many previous research projects include studies of
the smoke from the Kuwaiti oil fires and two international ACE studies (for Aerosol
Characterization Experiment), which are designed to shed light on the roles of aerosols in
global weather, water pollution and human disease. The most recent, ACE-Asia, operated
under National Science Foundation funding with 21 aerosol-sampling sites from Asia to
western North America from March through August 2001.
DELTA Group currently is continuing analyses of the 2001 ACE samples,
as well as studies of Alaskan air quality, the nature of diesel-vehicle exhaust, the
impacts of air pollution on human health in California's great Central Valley, and the
environmental health of the Lake Tahoe Basin. For more information, visit the DELTA Web
site at: http://delta.ucdavis.edu.
The University of California, Davis, is one of the world's leading
institutions in the environmental sciences. More than 250 faculty members support an
unmatched array of environmental programs in human and animal health, agriculture,
biological sciences, engineering, physical sciences, law, social sciences, literature and
the arts.
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