Cities and their associated industrial areas are dynamic entities that consume and metabolize atmospheric trace gases in daily and seasonal cycles. The metabolites of urbanization directly affect public health and the environment on local, regional, and global scales. The Urban Metabolism and Trace Gas Respiration project funded by the National Aeronautical and Space Administration (NASA) is studying urban and industrialized areas as entities that consume, metabolize and respire a wide range of trace gases. As part of this project, an urban footprint model is being developed to predict upwind pollutant source size and strength from downwind concentration measurements.
Three components comprise the urban footprint modeling strategy:
1) Mesoscale modeling of the regional wind field, 2) Application of a 3-d turbulence model simulating the urban landscape, 3) Application of the urban footprint model. The MM5 mesoscale meteorological model developed by Pennsylvania State University and the National Center for Atmospheric Research (NCAR) is a three-dimensional non-hydrostatic model. MM5 provides initial and boundary conditions to the fluids model TEMPEST developed by Battelle Memorial Institute's Pacific Northwest Laboratory. TEMPEST simulates the complex flows of the urban landscape, such as street canyon flows, the urban heat island effect, and building re-circulation zones, by solving the Reynolds averaged Navier-Stokes equations with a k-e turbulence closure formulation. The flow fields provided by TEMPEST will be utilized by the urban footprint model to provide an estimation of pollutant source strength and location. The focus is upon horizontal scales from 10's to hundreds of meters.
As a first step in the development of the urban footprint model, results from a preliminary field campaign will be correlated with the model results. The field campaign was conducted November 10-13, 1996 in Manchester, New Hampshire, where Methane (CH4) was sampled in real-time using a tunable infrared laser differential absorption spectrometer (TILDAS) system designed by Aerodyne Research Inc. Integrated samples of volatile organic compounds (VOCs) were also obtained throughout the urban area to characterize the mix of urban emissions. Manchester, NH is uniquely suited as an urban field study site because it is an isolated city with an active industrial area. Presented here are the first two phases of the urban footprint modeling strategy, where MM5 has been applied to simulate the mesoscale meteorology and provide initial and boundary conditions to TEMPEST simulating the idealized urban profile of Manchester, New Hampshire.