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RESIDENCE TIME MEASUREMENTS IN AN ARRAY OF BUILDINGS
Citation:
HEIST, D., L. BRIXEY, S. G. PERRY, AND G. E. BOWKER. RESIDENCE TIME MEASUREMENTS IN AN ARRAY OF BUILDINGS. Presented at PHYSMOD 2005 International Workshop, London, ON, CANADA, August 24, 2004 - August 26, 2005.
Impact/Purpose:
The objective of this task is to develop and evaluate numerical and physical modeling tools for simulating ground-level concentrations of airborne substances in urban settings at spatial scales ranging from ~1-10 km. These tools will support client needs in the areas of air toxics and homeland security. The air toxics tools will benefit the National Air Toxics Assessment (NATA) program and human exposure modeling needs within EPA. The homeland security-related portion of this task will help in developing tools to assess the threat posed by the release of airborne agents. Both sets of tools will consider the effects induced by urban morphology on fine-scale concentration distributions.
Description:
Transient concentration measurements were made to characterize residence times of pollutants in a street canyon within an array of buildings. The decay in pollutant concentration with time can be characterized by two time scales, the delay time and the decay time constant. The delay time represents the time required after a source is turned off for a decrease in concentration to be observed at the sampler. The decay time scale is a measure of how quickly a street canyon ventilates after the delay time has passed. Both of these times scales were found to decrease by 18-20% when the building height (H) directly upwind of the measurement point was increased from 1H to 3H, where H is the height of the other buildings in the array.