Simulating real-world exposures during emergency events: studying effects of indoor and outdoor releases in the Urban Dispersion Program in upper Manhattan, NY.

A prospective personal exposure study, involving indoor and outdoor releases, was conducted in upper Midtown Manhattan in New York City as part of the Urban Dispersion Program (UDP) focusing on atmospheric dispersion of chemicals in complex urban settings. The UDP experiments involved releases of very low levels of perfluorocarbon tracers (PFTs) in Midtown Manhattan at separate locations, during two seasons in 2005. The study presented here includes both outdoor and indoor releases of the tracers, and realistic scripted activities for characterizing near source and neighborhood-scale exposures using 1-min and 10-min duration samples, respectively. Results showed that distributions of individual tracers and exposures to them within the study area were significantly influenced by surface winds, urban terrain, and movements of people typical of urban centers. Although in general, PFT levels returned quickly to zero in general after cessation of the emissions, in some cases, the concentrations stayed at higher levels after the releases stopped. This is likely due to accumulation of the PFTs in some buildings, which then serve as "secondary sources" when outside levels are lower than indoor levels. Measurements of neighborhood-scale PFT concentrations (up to distances of several blocks away from the release points) provided information needed to establish a baseline for determining how different types of releases could affect exposures both to the general public and to emergency responders. These data highlight the factors impacting the toxic threat levels following releases of hazardous chemicals and provide supporting information for evaluating and refining protocols for emergency event response.