3.4 Understanding urban canopy-PBL dispersion interactions: a legacy from the SLC, OKC, and NYC urban tracer studies

Thursday, 27 January 2011: 2:15 PM
604 (Washington State Convention Center)
Robert D. Bornstein, San Jose State University, San Jose, CA; and M. J. Leach and M. Reynolds

Important insights from the Salt Lake City (SLC), Oklahoma City (OKC), and New York City (NYC) urban tracer studies concern the dynamic and thermodynamic interactions between urban canyons, the urban canopy layer, the urban roughness sub-layer, and the urban PBL, and how these interactions impact the transport and diffusion of pollutants across these interfaces.

This paper first reviews the increased understandings of the transport and diffusion process active in these layers, from microscale turbulent fluxes of heat and momentum to vertical convection to urban scale circulation patterns. The effects of these processes on the spread of passive pollutants in the horizontal and vertical on scales ranging from single building to streets and intersections to canyons and neighborhoods will then be illustrated. These processes will be illustrated by use of the mean and turbulent meteorological and tracer data collected during the SLC. OKC, and both NYC [Madison Square Garden (MSG) and Midtown] tracer release periods. Results from the many papers from these efforts will be synthesized in terms of the new information revealed concerning urban atmospheric meteorological and dispersion processes.

Specific results include PBL temperature and flow patterns during the MSG tracer release, as simulated by an urbanized (with the Martilli scheme) version of MM5, which showed divergent flow around Manhattan during this high speed synoptic-flow (and hence low urban heat island) period. For the NYC studies, model results are compared to direct measurements from wind profilers, building top acoustic sounders, and from an array of sonic anemometers located on building tops and in the canyons. Canyon wind patterns showed horizontal flows that impact building sides and then split to produce meter per second vertical velocities both upward and downward the building sides.

Other results include temperature, wind, and turbulence patterns from the OKC data, inferred from observations taken from the instruments platforms deployed throughout the urban area. Interesting coherent features appear in the wind and temperature vertical profiles observed just downwind of the urban core. The features appear related to shading by tall building structures in the business district.

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