Homeland Security

BIOMONITORING

Last Monday, scientists from several government agencies released two tracer gases in a 2-km² area of midtown Manhattan. In a series of experiments, they are tracking how harmful gases or particles might disperse through street canyons, subway tunnels, and buildings. Dubbed the Urban Dispersion Project, this Department of Homeland Security-sponsored effort aims to produce a computer model of airflow patterns that could help state and local officials better respond to an emergency or to a biological or chemical terrorist act.

On six days over a three-week period ending Aug. 26, sulfur hexafluoride and perfluorocarbons are to be released from three open-air sites within the designated area. Some 200 samplers will monitor the gases as they ride the wind. The monitors are positioned on streetlight poles, on rooftops, on subway platforms, and within an office building. In addition, 15 to 20 people equipped with personal sampling devices will walk the affected streets to monitor inhaled concentrations.

Samples collected from perfluorocarbon monitors will be taken to Brookhaven National Lab for analysis by gas chromatography, while those for sulfur hexafluoride will go to a National Oceanographic & Atmospheric Administration lab at Idaho Falls, Idaho, also for GC studies.

This August exercise follows an earlier round of testing that took place in midtown last March that discovered that wind patterns are best determined by equipment on rooftops, not at street level. A third run, with tracer gases being released in a subway, is slated for next spring.

Lead scientist K. Jerry Allwine, an engineer from Pacific Northwest National Lab, says the aim of these field exercises "is to get real-time data on how something moves through and around midtown. The data are then used to validate and improve computer models for planning purposes and for emergency response."