Environmental Engineering Reference
In-Depth Information
For air quality forecasts, the sophistication of UCP schemes in NWP models is
governed by operational requirements. To obtain products, that will help with guid-
ance in reducing poor air quality in street canyons, from forecast mode, may require
special ad hoc urban meteorological post processing. However, for applications such
as emission control strategies, where vertical profiles of the meteorological and tur-
bulent characteristics are needed in great detail, similar post-processing might not
be sufficient.
Studies to assess air pollution health effects are an important objective that may
be satisfied best with retrospective approaches. Population exposure modeling will
require highly detailed multi-pollutant and multi-scale air quality models, as well
as high-resolution urban morphology, population distribution, and human activities
databases (Baklanov et al., 2007). For these and similar applications, the emphasis
will be on implementing urban schemes at a grid resolution that can provide the
appropriate transport and turbulence details within the UC.
The fitness-for-purpose analysis also governs the choice of local-scale emergency
preparedness modeling for accidental biological, chemical, or nuclear releases, and
moreover, is clearly one of scale. For direct response and for operational pur-
poses where timeliness is important urban meteorological observations and/or fore-
cast products coupled with dispersion models are appropriate. For planning and
assessment purposes and for the near-sources region, obstacle-resolved modeling
approaches (e.g., CFD modeling) may be required. Such approaches will require
careful linkage to outputs of urban-scale models, and both will require basic build-
ing and vegetation descriptions. Ideally, specific urban feature effects that should be
incorporated into this type of application will include the following:
Impact of urban surfaces on pollutant deposition (e.g., vertical walls, building
materials and structure, vegetation)
Information regarding chemical transformation such as lifetime of chemical
species (e.g., inside street canyons), heterogeneity of solar radiation (street shad-
ows, albedo, and emissivity), and specific aerosol dynamics in street canyons
(e.g., resuspension processes)
Very detailed, high-resolution data on the mobile emission of pollutants
Indoor-outdoor pollutant exchange information
15.4.3 Multiscale Atmospheric Environment Modeling
Air quality in urban areas is influenced by local pollutant emission sources as well
as transport of species on regional and global scales. In turn, transport of air pollu-
tants from urban areas will impact on regional and global scale air quality. Current
atmospheric-chemical-transport (ACT) models apply model nesting approaches as
a means for treating the up- and down-scaling to account for this multi-scale dimen-
sion (Moussiopoulos, 1995; Fernando et al., 2001; Baklanov, 2007).
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