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Model Report

Urban Airshed Model-V v1.50

Last Revision Date: 08/31/2009 View as PDF
General Information Back to Top
Model Abbreviated Name:

UAM-V v1.50
Model Extended Name:

Urban Airshed Model-V v1.50
Model Overview/Abstract:
The UAM-V Model is a three-dimensional, multi-scale photochemical grid model that calculates concentrations of pollutants by simulating the physical and chemical processes in the atmosphere. The model is the latest of the Urban Airshed Model (UAM) lineage, which was initiated in the early 1970s and has undergone nearly continuous cycles of application, performance evaluation, update, extension, and improvement. The basis for the UAM is the atmospheric diffusion or species continuity equation. This equation represents a mass balance that includes all of the relevant emissions, transport, diffusion, chemical reactions, and removal processes in mathematical terms. Because it accounts for spatial and temporal variations as well as differences in the reactivity of emissions, the UAM is ideal for evaluating the air-quality effects of emission control scenarios. It does this by first replicating a historical ozone episode to establish a base-case simulation. Model inputs are prepared from observed meteorological, emission, and air quality data for the episode days using prognostic meteorological modeling and/or diagnostic and interpolative modeling techniques. The model is then applied with these inputs, and the results are evaluated to determine its performance. Once the model results have been evaluated and determined to perform within prescribed levels, the same base-case meteorological inputs are combined with projected emission inventories to simulate possible future emission scenarios.

The model contains the following features: capability of simulating multiple nested grids of variable resolution, two-way communication between nested grids, multiple coordinate system capabilities, and plume-in-grid (PiG) treatment. The UAM-V also includes Process Analysis capabilities that allow the user to quantify the contributions from the physical and chemical processes to simulated concentrations in selected grid cells. The model employs the Carbon Bond V chemical kinetics mechanism, an updated version CB-IV mechanism (Gery, at al., 1989). The UAM-V has been applied to simulate tropospheric ozone concentrations on multiple scales for a range of time periods (days, months, seasons, year). The model requires input data specifying the emissions and initial and boundary concentrations of gaseous precursors of ozone (VOC, NOx, and CO). The model also requires a full set of three-dimensional meteorological inputs, which can be provided by dynamic meteorological models (such as MM5) or diagnostic models (such as DWM). The UAM-V also has the capability of running without photochemistry (nonreactive), to simulate urban- or regional-scale CO concentrations.

UAM-V includes the Ozone and Precursor Tagging Methodology (OPTM) which allows estimates of source contributions to ozone formation to be made during a simulation.

Keywords:
Model Technical Contact Information:
Sharon Douglas
ICF International
sdouglas@icfi.com
415 507-7108

Information is also available through EPA's Support Center for Regulatory Atmospheric Modeling website at http://www.epa.gov/scram001/photochemicalindex.htm

Model Homepage: http://www.uamv.com Exiting the EPA Site
Substantive Changes from Prior Version: Latest version includes the Carbon Bond V chemical mechanism and OPTM for estimating source contributions to ozone.

User Information Back to Top
Technical Requirements
Computer Hardware
PC or Workstation, 100 Mb memory, 20 Gb disk space
Compatible Operating Systems
Unix/Linux
Other Software Required to Run the Model
Fortran 77
Download Information
www.uamv.com exit EPA
Using the Model
Basic Model Inputs
Meteorological data required by the model include hourly, three-dimensional inputs of horizontal winds, temperature, pressure, water vapor, and vertical turbulent exchange coefficients. Hourly, gridded two-dimensional inputs are required for: landuse, total ozone column, turbidity, and albedo. In addition, the model requires information regarding the heights (above ground) of the specific layers used in the simulation and the pressure at the layer midpoints. Estimates of cloud cover, liquid water concentration, and rainfall rate are optional.

Air quality data are required to specify the initial concentration fields and the concentrations along the boundaries (top and lateral) of the modeling domain.

The emission inputs include gridded, hourly estimates of gaseous species required by the CB-IV, including speciated hydrocarbons (VOC), NOx as NO and NO2, and CO for all anthropogenic and biogenic sources. The model requires specific source information for stationary sources, including stack location coordinates, height, diameter, exit velocity, and exit temperature for calculating plume rise. For CO modeling, sources of CO emissions are all that is required.

Other input requirements of UAM-V include the chemical reaction rates file, a file that specifies the selected cell aggregation and grid nesting attributes, and a file that specifies the attributes of the simulation, including grid definition, time step, output options (such as Process Analysis), and other options.

Basic Model Outputs
The output provided by the UAM-V model includes a three-dimensional array of pollutant concentrations for all species simulated in two files: an average file provides hourly (or other averaging period specified by the user) concentrations that are an average of the concentrations at each advection time step; and an instantaneous file, that provides concentration fields at the beginning of the hour (or other user-specified time period). The model also provides a full list of input specifications, including emission summaries, mass fluxes across boundaries, history of the simulation, and a record of useful diagnostic parameters for each time step of the simulation.
User Support
User's Guide Available?
www.uamv.comexit EPA

User Qualifications
Some prior experience in modeling and atmospheric science is helpful. User should be comfortable running applications in a Unix/Linux environment. User must be capable of organizing and handling large data sets.

Model Science Back to Top
Problem Identification
UAM-V is a three-dimensional grid model designed to calculate the concentrations of the chemically reactive species involved in the formation of urban smog. It is also capable of calculating the concentrations of inert species such as CO. The basis for the model is the atmospheric diffusion or species continuity equation. This equation represents a mass balance in which all of the relevant emissions, transport, diffusion, chemical reactions, and removal processes are expressed in mathematical terms. The model solves the species continuity equation using the method of fractional steps, in which the individual terms in the equation are solved separately. The maximum advective time step for stability is a function of the grid size and the maximum wind velocity or horizontal diffusion coefficient. Vertical diffusion is solved on fractions of the advective time step to keep their individual numerical schemes stable. A typical advective time step for an urban scale (4 km) grid spacing is 2–5 minutes.

Model inputs are prepared for meteorological and emissions data for the simulation days. Once the model results have been evaluated and determined to perform within prescribed levels, a projected emission inventory can be used to simulate possible policy-driven emission scenarios.

The representation of the various processes in the model is based on current scientific understanding.

References are given in the User’s Manual.

Summary of Model Structure and Methods
Emissions
Anthropogenic and biogenic emissions are spatially allocated and provided to the model in gridded form. The emissions are temporally allocated throughout the simulation period to emulate the temporal features of the total daily emissions. Sources with no (or small) plume rise are injected into the first layer of the model. Emissions of sources with plume rise are emitted into the upper layers of the model, depending on the hourly effective plume rise. Specific sources can also be treated (user-specified) with a subgrid-scale plume-in-grid algorithm, which better treats the diffusion, transport, and chemistry of the emissions by minimizing near-source dispersion.

Concentrations
Concentrations of each pollutant are calculated for all grid cells within the modeling domain. The Process Analysis feature allows the user to quantify the contribution of the physical and chemical processes to the concentration in one or more cells.

Further Information in "Key Limitations to model Scope" and "Case Studies" Sections (below)

Model Evaluation
Jiang, W., M. Hedley, and D. L. Singleton, 1998. “Comparison of the MC2/CALGRID and SAIMM/UAM-V Photochemical Modeling Systems in the Lower Fraser Valley, British Columbia. Atmos. Environ., 32: 2969-2980.

Douglas, S. G., H. H. Tunggal, G. Mansell, and J. L. Haney. 1998. “Subregional Photochemical Modeling Analysis for Atlanta, Birmingham, and the Eastern Gulf Coast Area: Input Preparation and Model Performance Evaluation.” Systems Applications International, Inc., San Rafael, California (SYSAPP-98/43d).

Lehman, E., 1998. “The Predictive Performance of the Photochemical Grid Models UAM-V and CAMx for the Northeast Corridor”. Presented at the Air & Waste Management Association 91st Annual Meeting & Exhibition, San Diego, California, June 14-18, 1998.

Sonoma Technology, Inc., 1997. Evaluation of UAM-V Model Performance in OTAG Simulation: Summary of Performance Against Surface Observations, January 1997. Final Report STI-996120-1605-FR, Sonoma Technology, Inc. Santa Rosa, California, Prepared for the Ozone Transport Assessment Group.

Gery, M. W., G. Z. Whitten, J. P. Killus, and M. C. Dodge. 1989. A photochemical kinetics mechanism for urban and regional scale computer modeling. J. Geophys. Res., 94(D10):12,925-12,956

Smagorinsky, J. 1963. General circulation experiments with the primitive equations: I. The basic experiment. Mon. Wea. Rev., 91:99-164.

Turner, D. B., T. Chico, and J. A. Catalano. 1986. TUPOSCA Multiple Source Gaussian Dispersion Algorithm Using On-Site Turbulence Data. U.S. Environmental Protection Agency, Research Triangle Park, North Carolina (EPA-600/8-86/010).

Wesely, M. L. 1989. Parameterization of surface resistances to gaseous dry deposition in regional-scale numerical models. Atmos. Environ., 23:1293-1304.

Key Limitations to Model Scope
Highest resolution is about 1 – 2 km.
Long simulation periods and high resolution require considerable computer resources.
Preparation of input data for large applications can be time and computer resource intensive.

Case Studies
Douglas, S. G., Y. Wei, A. B. Hudischewskyj, T. C. Myers, and J. L. Haney. 2007. Analysis of Three 2005 Crittenden County Ozone Study (CCOS) Episodes Using Air Quality Modeling Tools, Report (07-033). Arkansas Department of Environmental Quality (ADEQ).

Douglas, S. G., Y. Wei, J. Mangahas, A. B. Hudischewskyj, A. R. Alvarez, G. L. Glass, W. S. Hartley, and J. L. Haney. 2004. Early Action Compact Ozone Modeling Analysis for the State of Tennessee and Adjacent Areas of Arkansas and Mississippi, Technical Support Document (04-012). Southeast States Air Resource Managers (SESARM), Arkansas-Tennessee-Mississippi Ozone Study (ATMOS) Operations Committee.

Douglas, S. G., Y. Wei, A. B. Hudischewskyj, A. R. Alvarez, and R. S. Beizaie. 2004. Gulf Coast Ozone Study (GCOS) Modeling Analysis: Phase II Methods and Results, Final Report (04-024). Southeast Air Resources Managers (SESARM) and GCOS States Southern Company.

BAAQMD. 1998. “Bay Area – North Central Coast Photochemical Modeling Investigation of Ozone Formation and Transfer”

Douglas, S. G., N. K. Lolk, and J. L. Haney, 1996, “Investigation of the Effects of Horizontal Grid Resolution on UAM-V Simulation Results for Three Urban Areas”, Report SYSAPP-96/98, October 21, 1996. Systems Applications International, San Rafael, California.

Key Limitations to Model Scope
Plume Behavior
The plume rise for user-specified sources is calculated based on the plume rise treatment developed for the Gaussian dispersion model TUPOS (Turner et al., 1986). For user-specified sources, the dispersion, diffusion, chemical transformation, and transport of emissions are calculated with the Plume-in-Grid algorithm. Emissions are released from the source in a series of “puffs”. When the user-specified plume size in the puff is equal to a portion of the grid cell, the plume mass is injected into and handled henceforth by the grid model.

Horizontal Winds
The UAM-V requires gridded, three-dimensional winds in the form of u and v components, which must be specified either at each grid cell center or staggered to horizontal cell interfaces.

Vertical Wind Speed
The UAM-V model calculates vertical winds at each layer interface using the mass-continuity relationship using the horizontal wind components.

Case Studies
Horizontal Dispersion
Horizontal diffusivities are calculated with the UAM-V based on deformation characteristics of the horizontal wind (Smagorinsky, 1963).

Vertical Dispersion
Vertical turbulent exchange coefficients are estimated using either output from a prognostic meteorological model, such as MM5, or a preprocessor that utilizes gridded UAM-V input wind and temperature information.

Chemical Transformation
The UAM-V uses Version V of the Carbon Bond Mechanism (CB-V).

Removal Processes
The UAM-V dry deposition algorithm is based on a scheme by Wesely (1989), where the deposition velocity is a function of aerodynamic, boundary layer, and surface resistance. The aerodynamic resistance is dependent on the surface characteristics and atmospheric stability conditions. The boundary or quasilaminar resistance represents the process of molecular diffusion of the transport of pollutant around solid objects and is dependent on the ratio of the air kinematic viscosity to the molecular diffusivity. The surface resistance is a set of resistances associated with vegetation types and surface soil, litter, and water, and are derived based on the input land use characteristics. Wet deposition, which is optional, calculates the removal of aerosol and soluble gas species using gridded, hourly rainfall rates.


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