Trade Center air laden with
very fine particles, DELTA scientists find
The UC Davis DELTA Group took air
samples about a mile from the World Trade Center in early
October 2001, several weeks after the towers collapsed. They
identified high levels of coarse particles, above, which included powdered concrete and glass with a coating
of combustion products, in size range of 5 to 12 micrometers
diameter. Very fine particles were found at levels not previously
seen in ambient air samples. By Michael Dunlop and Aaron Broumas.
In the most thorough analysis yet of the dust and smoke blown through
lower Manhattan after the collapse of the World Trade Center, UC
Davis scientists identified unprecedented clouds of very fine particles,
which can be riskier to human health than larger, coarse particles.
air from Ground Zero was laden with extremely high amounts of very
small particles, probably associated with high temperatures in the
underground debris pile," says Thomas Cahill, UC Davis professor
emeritus of physics and atmospheric sciences. "Normally, in
New York City and in most of the world, situations like this just
Cahill heads the UC Davis DELTA Group (Detection and Evaluation
of Long-range Transport of Aerosols), a collaborative association
of aerosol scientists at several universities and national laboratories,
which monitors atmospheric conditions associated with global warming,
weather, disasters and other events.
Group collected air samples at therequest of the U.S. Department
of Energy from Oct. 2 through mid-December, with a rooftop air monitor
about 1 mile north-northeast of Ground Zero.
for October were released in early February, and Cahill testified
at an investigative hearing before the national ombuds-person for
the U.S. Environmental Protection Agency on Feb. 23.
were collected continuously in eight separate-size modes from coarse
(12 micrometers diameter) to ultra-fine (0.09 micrometers diameter),
and were analyzed for dozens of substances that are likely to be
associated with burning office buildings.
Coarse particles are typically filtered by the nose or coughed out
of the throat and upper lungs, but they can irritate the mucous
membranes and aggravate pre-existing breathing problems such as
asthma. Very fine particles, however, can travel deep into human
lungs, and are typically removed from the lungs through the bloodstream
and heart, increasing the possibility of more serious health impacts.
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 says. "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."
all the air samples from the trade center site also carried high
concentrations of coarse particles. "These particles simply
should not be there," Cahill says. "It had rained, sometimes
heavily, on 6 days in the prior 3 weeks. That rain should have settled
these coarse particles." The finding suggests that coarse particles
were being continually generated from the hot debris pile.
in the very fine mode, such as vanadium, were found at the highest
levels ever recorded in air in the United States. Although some
asbestos was used in the buildings for fireproofing and in floor
tiles, the DELTA group found very few asbestos fibers, even in the
very fine particles.
indicates that ambient air in New York City is no longer influenced
by the World Trade Center collapse, especially since the fires are
out and the debris pile has cooled, Cahill says. However, the presence
of large amounts of very fine particles as late as October means
that the cleanup of indoor air should be undertaken carefully, he
warns. Very fine particles penetrate crevices and fabrics in a way
that normal dust doesn't, and they are easily resuspended, which
can re-expose the room's occupants.
information, go to: http://delta.ucdavis.edu
Carbon dioxide hampers nitrate incorporation
Wheat was grown in a controlled
environmental chamber under elevated carbon dioxide. Plants
received ammonium (left) or nitrate (right) as their sole
nitrogen source. Leaves of plants receiving nitrate are yellowish-green,
signaling that they are not assimilating the nutrient as well
as plants receiving ammonium. Photo from UC Davis
Nitrate fertilizer is not nearly as efficient as ammonium fertilizer
when atmospheric carbon dioxide levels are unusually high, according
to a study by two UC Davis professors.
of atmospheric carbon dioxide associated with global warming can
interfere with a plant's ability to incorporate nitrogen, Arnold
Bloom and David Smart reported in the Feb. 5 Proceedings of the
National Academy of Sciences. Carbon dioxide concentrations
have increased by an estimated 30% during the past two centuries
and are likely to double during the next century.
Farmers and gardeners commonly apply nitrogen-rich fertilizers to
their crops in order to enhance yields. The UC Davis scientists
studied how wheat plants respond to being fertilized with two different
forms of nitrogen, nitrate and ammonium, under varying concentrations
of atmospheric carbon dioxide.
receiving ammonium responded much more to the increased carbon dioxide
than did the plants receiving nitrate, the scientists found. Elevated
carbon dioxide levels inhibited the processing of nitrate in the
wheat leaves. When atmospheric carbon dioxide rose to nearly twice
the normal level, the leaves of plants receiving ammonium increased
in size by nearly 49%, while plants receiving nitrate increased
by only 24%.
the protein content of the wheat plants receiving ammonium increased
73% under elevated carbon dioxide, compared to only 32% for those
receiving nitrate, suggesting that rising atmospheric carbon dioxide
levels might diminish the nutritional quality of grain receiving
nitrate fertilizer. The work has since been repeated in tomatoes,
with similar results.
"We expect that the data will have real-world implications
for crop production," Bloom says. "In well-drained soils
generally devoted to wheat production, nitrate is the common form
of nitrogen available. The study suggests that a shift to increase
ammonium availability might be needed."
plant and tree species in natural ecosystems that depend on nitrate
conversion into amino acids in their leaves are likely to be at
a competitive disadvantage with those species that are either able
to convert nitrate into amino acids in their roots or use ammonium
as their predominant nitrogen source. "This may result in significant
changes in the distribution of plants in the wild as atmospheric
carbon dioxide levels continue to rise," Bloom says
Super-sensitive nitrogen dioxide detector
identifies greenhouse gases
Doug Day checks the performance
of the world's most sensitive nitrogen dioxide detector, in
a trailer at the UC Blodgett Forest Research Center in El
Dorado County. The detector found high levels of previously
unquantified organic nitrogen compounds, an observation that
current models cannot adequately explain. Photo by Tim Albrecht.
With the aid of the most sensitive nitrogen dioxide detector
in the world, UC Berkeley chemists can now quantify certain important
contributors to air pollution and global warming.
nitrogen oxide compounds are emitted by automobiles, industrial
smokestacks and other sources; they react with natural hydrocarbons
from vegetation to produce ozone smog. "Ozone in the troposphere
has doubled in the past century, contributing 10% to 15% of the
human additions to the greenhouse effect," says UC Berkeley
chemistry professor Ronald C. Cohen. "All of this is driven
by nitrogen oxides."
however, as much as half the resulting nitrogen oxides have been
unaccounted for in the atmosphere, leaving air pollution models
incomplete. Today's smog monitors measure essentially the sum total
of all nitrogen oxides in the air, and are unable to break them
down into the specific amount of each nitrogen oxidecontaining
4 years, Cohen and his laboratory colleagues developed a new detector,
called thermal dissociation-laser induced fluorescence (TD-LIF),
which can monitor nitrogen oxide compounds continuously with sensitivity
down to 30 parts per trillion. The technique is a thousand times
more sensitive than needed for today's pollution monitoring and
sensitive enough for studies in remote locations.
the detector in downtown Houston and in a remote Sierra Nevada forest,
the scientists detected large amounts of organic nitrogen oxide
compounds called alkyl nitrates, which were thought to be only a
minor constituent of smog.
we want to understand quantitatively the effect of local pollution
on the global scale, we need to know how and in what form nitrogen
oxide is transferred to the rest of the globe," Cohen says.
was published in the March 2002 issue of the Journal of Geophysical
Research-Atmospheres, and is supported by the National
Aeronautics and Space Administration.
Compiled from U.C. and other news sources.