Urban Morphology for Houston to Drive Models-3/CMAQ at Neighborhood Scales

4.6 URBAN MORPHOLOGY FOR HOUSTON TO DRIVE MODELS-3/CMAQ AT NEIGHBORHOOD SCALES
Jason Ching1, Tanya L. Otte1, Sylvain Dupont2, Steve Burian3, and Avraham Lacser4
1 Atmospheric Sciences Modeling Division, NOAA ARL, Research Triangle Park, North Carolina
On assignment to the National Exposure Research Laboratory, U.S. EPA
Postdoctoral Fellow with the University Corporation of Atmospheric Research, Boulder, Colorado
department of Civil Engineering, University of Arkansas, Fayetteville, Arkansas
4lsrael Institute for Biological Research, Ness Ziona, Israel
1. INTRODUCTION
Air quality simulation models applied at various
horizontal scales require different degrees of treatment
in the specification of the underlying surfaces. As we
model neighborhood scales (~1 km horizontal grid
spacing), the representation of urban morphological
structures (e.g., building and area distributions, and
compositional materials for impervious structures such
as roads and parking areas) requires much greater
detail. At the neighborhood scale, we expect that the
heterogeneities of structures within the urban canopy
(i.e., the layer between the surface and the tops of the
buildings) will exert a strong influence on the urban
boundary layer (UBL) wind and thermodynamic
structure and a subsequent effect on the pollutant
dispersion and resulting air quality predictions.
The U.S. EPA Models-3 Community Multi-scale Air
Quality (CMAQ) modeling system (Byun and Ching
1999) will be applied at neighborhood scales to drive
human exposure models and for human risk
assessments purposes (Ching et al. 2000, 2002).
CMAQ will be used to support modeling studies and air
quality assessments of ozone, particulate matter(PM),
and air toxics in Houston, Texas, using the Penn
State/NCAR Mesoscale Model (MM5) (Grell et al. 1994)
to provide meteorological input. This application
requires developing more detailed treatment of the
influence of urban structures in MM5 and using
additional urban morphological databases as input.
2. APPROACH
In this study, MM5 is modified to incorporate
formulations and urban morphology for (1) an advanced
urban soil and canopy model that adjusts the
thermodynamics of the UBL, and (2) the additional drag
and turbulence induced by the presence of buildings
and trees. The subsequent meteorological fields will
better represent the effects of the urban areas on the
momentum, turbulent kinetic energy (TKE), and energy
balance at the neighborhood scales.
2.1 Modeling the Urban Environment
The surface dynamic and thermodynamic effects in
MM5 are represented by momentum flux, sensible heat
flux, and latent heat flux terms. Idealized horizontally
uniform surface characteristics, boundary layer flows
and structures are typically modeled using roughness
* Corresponding author address'. Jason Ching,
AMD/NERL/USEPA (MD: D243-03), RTP, NC 27711:
email: ching.jason@epa.gov
length similarity formulations for momentum,
temperature, and humidity. The basis of these
formulations is the assumption that surface roughness
elements are both small and statistically uniform relative
to height, and the surface exchange coefficients use
Monin-Obukhov similarity theory. However the theory
generally requires statistical stationarity and spatial
homogeneity, and is not satisfied in the urban
atmosphere at the neighborhood scale. It does not, for
example, model the wind profiles structure and TKE
profiles in and above the urban canopy (Rotach 1995).
To address this problem, we extend the current
theory by introducing an urban canopy-atmospheric
interface method formulated for incorporating urban
structures and materials. We adapt the methodology in
Dupont (2001) and Dupont et al. (2002) which use an
urban soil model, SM2-U, coupled with the French
meteorological model, SUBMESO, to produce
simulations of the UBL at fine grid resolution. The basis
of the SM2-U is the model of Noilhan and Planton
(1989). The extension to urban surfaces is the inclusion
of an urban canopy that accounts for the heat stored by
the building walls and radiative trapping by a street
canyon effective albedo parameterization deduced
following Masson (2000). In the Houston modeling
effort, SM2-U is coupled with MM5.
In addition, an urban canopy parameterization was
introduced into MM5 to account for drag exerted by
urban structures, the enhancement of TKE (especially
near the tops of the buildings), and the energy budget at
the street level and between buildings. This urban
canopy parameterization is also designed to effectively
simulate the heterogeneous urban environment by
allowing more urban land use subcategories than are
part of the standard MM5 release. Otte and Lacser
(2001) and Lacser and Otte (2002) show that using the
urban canopy parameterization can improve the wind,
temperature, and TKE fields in 1.3-km urban simulations
with MM5. Preliminary simulations with the urban
canopy parameterization also illustrated the need for
heterogeneous representation of the urban morphology.
2.2 Urban Morphological Parameterizations
Recent technology including stereo
photogrammetry and/or airborne lidar data is capable of
producing 3-D digital building and tree datasets; this
enables the required morphological parameters to be
accurately determined for the location of interest using
numerical analysis techniques. Computer-based
analysis techniques (e.g., ArcView GIS tools) and
methodologies described in Burian et al. (2002) are
applied to various datasets, including digitized buildings,

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land use/land cover, and other essential datasets for the
Houston area.
This effort produces a database of urban
morphology parameters to drive and perform the
requisite air quality and human exposure assessments.
Two methods for deriving urban morphology for
modeling purposes are developed based on the amount
and spatial coverage of 3D building data information
and land use database. First, and ideally, when building
and vegetation data covers the full simulation domain,
we can directly derive and apply the urban
morphologies directly to our simulation domain.
Second, with sparser data sets, relationships that
correlate building morphological characteristics to
underlying land use type are developed and applied.
Subsequently, the morphological characteristics will be
extrapolated throughout the simulation domain using the
land use/land cover dataset.
Application of the urban canopy parameterizations
described in Dupont (2001) and Lacser and Otte (2002)
requires incorporating urban morphological data into
MM5, including:
•	Mean and standard deviation of building height
•	Mean and standard deviation of vegetation height
•	Building height histograms
•	Area-weighted mean building height
•	Area-weighted mean vegetation height
•	Surface area of walls
•	Plan area fraction as a function of height above the
ground surface
•	Frontal area index as a function of height above the
ground surface
•	Height-to width ratio
•	Sky view factor
•	Roughness length
•	Displacement height
•	Surface fraction of vegetation, roads, and rooftops
•	Mean orientation of streets
•	Impervious areas directly connected to the draining
network
We are accumulating several commercial(and other
publically) available datasets of digital elevation and
terrain data in both raster and vector form for Harris
County (which includes Houston) and surrounding areas
into a GIS database. Further processing will be
performed to differentiate buildings from tree elements.
Then, we generate gridded values of the average values
for the above parameters for desired grid resolutions of
the coupled urban energy budget and mesoscale
meteorological models. Finally, to extrapolate the land
surface parameterization beyond the aerial extent of the
digital database, average parameters will be computed
for several urban land use categories. The data
processing task will require tested techniques to be
applied to an areal extent well beyond the size areas
analyzed in past research efforts (Burian et al., 2002).
Disclaimer. The information in this manuscript has been
prepared under funding by the United States
Environmental Protection Agency. It has been
subjected to Agency review and approved for
publication. Mention of trade names or commercial
products does not constitute endorsement or
recommendation for use.
3. REFERENCES
Burian, S. J., M. J. Brown, and S. P. Linger, 2002:
Morphological analysis of buildings in downtown
Los Angeles, California. LA-UR-02-0781 Los
Alamos National Laboratory, 66 pp.
Byun, D. W., and J. K. S. Ching, 1999: Science
algorithms of the EPA Models-3 Community
Multiscale Air Quality (CMAQ) Modeling System.
EPA-600/R-99/030, U.S. EPA.
Ching, J., A. Lacser, D. Byun, and W. Benjey, 2000: Air
quality modeling of PM and toxics at neighborhood
scales to improve human exposure assessments.
Third Sym. on the Urban Environment, Davis, CA
Amer. Meteor. Soc. P96-97.
Ching, J., A. Lacser, T. L. Otte, J. Herwehe, and D.
Byun, 2002: Neighborhood scale modeling of PM2.5
and air toxics concentration distributions to drive
human exposure models. Preprints, 12th Joint AMS
Conf. on Air Pollution Meteorology with the AWMA,
Amer. Meteor. Soc., Norfolk, VA.
Dupont, S., 2001: Modelisation dynamique et
thermodynamique de la canopee urbaine:
realisation du modele de sols urbains pour
SUBMESO. Ph.D. thesis, ECN-Universite de
Nantes, France.
Dupont, S., I. Calmet, and P. Mestayer, 2002: Urban
canopy modeling influences on urban boundary
layer simulation. Preprints, Fourth Sym. on the
Urban Environment, Amer. Meteor. Soc., Norfolk,
VA.
Grell, G., J. Dudhia, and D. R. Stauffer, 1994: A
description of the fifth-generation Penn State/NCAR
mesoscale model (MM5). NCAR Tech. Note
NCAR/TN-398+STR, 138 pp.
Lacser, A., and T. L. Otte, 2002: Implementation of an
urban canopy parameterization in MM5. Preprints,
Fourth Sym. on the Urban Environment, Amer.
Meteor. Soc., Norfolk, VA.
Masson, V., 2000: A physically-based scheme for the
urban energy budget in atmospheric models.
Bound-Layer Meteor., 98, 357-397.
Noilhan, J., and S. Planton, 1989: A simple
parameterization of land surface processes for
meteorological models. Mon. Wea. Rev., 117, 536-
549.
Otte, T. L, and A. Lacser, 2001: Implementation of an
urban canopy parameterization in MM5 for meso-
gamma-scale air quality modeling applications.
Preprints, Ninth Conf. on Mesoscale Processes,
Amer. Meteor. Soc., Ft. Lauderdale, FL, 78-81.
Rotach, M., 1995: Profiles of turbulence in and above an
urban street canyon. Atmos. Environ., 29, 1473-
1486.

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4. TITLE AND SUBTITLE: Urban Morphology for Houston to Drive
Models-3/CMAQ at Neighborhood Scales.
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J. Ching, T. Otte, S. Dupont S. Buriaru and A. Lacser
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National Exposure Research Laboratory -RTP, NC
ORD, U.S. EPA, Research Triangle Park, N.C. 27711
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13. ABSTRACT (Maximum 200 words)
Air quality simulation models applied at various horizontal scales require different degrees of treatment in the
specification of the underlying surfaces. As we model neighborhood scales (~1 km horizontal grid spacing), the
representation of urban morphological structures (e.g., building and area distributions, and compositional materials
for impervious structures such as roads and parking areas) requires much greater detail. At the neighborhood scale,
we expect that the heterogeneities of structures within the urban canopy (i.e., the layer between the surface and the
tops of the buildings) will exert a strong influence on the urban boundary layer (UBL) wind and thermodynamic
structure and a subsequent effect on the pollutant dispersion and resulting air quality predictions.
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