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Brookhaven scientists aid in homeland security field study

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If an industrial accident or a terrorist act released dangerous contaminants into the atmosphere in New York City, the city’s first responders would have to decide quickly whether people should shelter in place or be evacuated, and what evacuation routes should be considered. In the future they will be aided in making those decisions by information gathered during the New York City Urban Dispersion Program field studies, conducted in the city’s urban canyons in March and August of 2005.

The field studies were part of the $10 million Urban Dispersion Program, sponsored by the U.S. Department of Homeland Security, the Defense Department’s Defense Threat Reduction Agency, the Environmental Protection Agency (EPA), and the Department of Energy (DOE). Data gathered from the study will help improve existing models of how a gas or chemical release might move around Manhattan’s tall buildings and canyons. Emergency management, law enforcement, and intelligence personnel use these models to plan for, train for, and respond to potential terrorist attacks and accidents involving harmful airborne contaminants.

“We are interested in how contaminants behave in very complicated urban canyon environments like New York City,” said Paul Kalb of Brookhaven Lab’s Environmental Sciences Department. “Anyone who’s been to the city has observed that the flags on one side of the street may be blowing one way while those on the other side of the street are blowing in the complete opposite direction.”

The March field study consisted of two days of detailed meteorological observations while scientists released a colorless, odorless, harmless “tracer” gas near Madison Square Garden. In six days of August experiments, the scientists released either perfluorocarbon (PFT) or sulfur hexafluoride at a number of outdoor locations. On several of those test days, small amounts of the gases were also released and tracked inside a Manhattan office building and in several subway stations.

“Many people may not realize that a few days of actual experimentation requires months of planning and preparation,” said Brookhaven’s John Heiser, the tracer team’s principal investigator for the project. “Hundreds of samplers, thousands of sample tubes, scores of approvals, in addition to the placement of meteorological equipment, route planning and many other details all require a massive, unseen effort by all involved.”

“Everyone worked in perfect harmony and did so on a very tight schedule,” he said, adding that he was impressed by the professionalism of the Brookhaven team. “I also enjoyed the spirit of cooperation shown to us by the various city, state, and federal agencies who assisted us.”

On each study day, scientists and students tracked the winds and the dispersion of the colorless, odorless, and non-toxic gases with a variety of samplers, some located on rooftops, other placed in baskets attached to lampposts. Mobile air samplers were also carried by students positioned on street corners, and by EPA employees who walked along assigned routes, periodically capturing a sample of air from the invisible plumes. A DOE van equipped with state-of-the-art analytical equipment cruised the streets of the midtown area providing near “real-time” data on the plume location and concentration. Built and calibrated at Brookhaven, the van-mounted instrument was developed for Keyspan to locate leaks in underground pipes. At the end of each test day, the tracer team members dismantled all the equipment and collected samples for analysis back at the Lab.

R. Michael Reynolds and his team from the Earth Science Systems Division provided precise meteorological measurements. “Computer models on many scales and with resolutions ranging from kilometers down to one meter will be evaluated with the meteorological and dispersion data we provide here,” Reynolds said. “It is essential that our meteorological data is as good as it can be, because once a model is shown to replicate our measurements, it can be applied with greater confidence to the entire neighborhood.”

Additional tests are planned for 2006. These experiments will add to the team’s knowledge of how weather conditions affect air dispersion. Previous field studies were conducted in Salt Lake City in 2000 and Oklahoma City in 2003.


More information is available at http://urbandispersion.pnl.gov


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