Trade Center Air Held Unprecedented Amounts of Very Fine
Particles, Silicon, Sulfates, Metals, Say UC Davis Scientists

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.

Media contact(s):
Sylvia Wright , (530) 752-7704 , [log in to unmask]