Offshore and Coastal Dispersion (OCD) Model
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Transcript of Offshore and Coastal Dispersion (OCD) Model
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Offshore and Coastal Dispersion (OCD) ModelHeather Groce
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Outline
I. IntroductionII. Methodology and ApplicationsIII. InstallationIV. UseV. Case StudyVI. Summary
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Introduction to OCD
Simulates offshore emissions from point, area, or line sources to receptors on land or water
Hourly, steady-state Gaussian model Q: Why is it necessary to have a
model specifically dedicated to a pollutant traveling from over water to over land?
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How was OCD developed? In 1980, a model was needed that
would handle off-shore emissions Adapted from MPTER This model added overwater plume
transport and dispersion Also incorporated changes as plume
crosses shoreline
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How does OCD work?
Three major components: Overwater subroutines that are new
algorithms based on overland boundary layer dynamics
Overland subroutines from MPTER Subroutines from existing
models to describe dispersion in complex terrain
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Overland vs. Overwater
Overwater mixing height is less than overland mixing height (why?)
Overwater mixing depth can vary from 100 m to 500 m
Different variations during the day and year
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Applications
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What data is needed?
Domain of model and defined coast Meteorological data (e.g. wind
speed) Source data (e.g. emission rate) Receptor data (e.g. elevation)
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Importance of meteorological data measurements Onsite overwater meteorological data (hard
to obtain) Representative overwater meteorological
data Representative overland meteorological data
Wind speed and direction Mixing height Overwater air temperature Relative humidity Sea surface temperature
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Some Definitions
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Installation
Code can be downloaded from the EPA’s Preferred/Recommended Models webpage
User-friendly interfacehttp://www.epa.gov/ttn/scram/dispersion_prefrec.htm
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Using OCD
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Starting a New Model
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Input Menu
Nine input windows:
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Run Information
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Model Domain
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Sources
New Inputs:• Stack angle
from the vertical
• Height of stack top above its base*
• Height of building at or near stack base
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Dispersion
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Receptors
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Types of Receptors
Discrete Polar Cartesian
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Meteorology
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Sources of Meteorological Data ASCII, included in Control File Binary, in Separate PCRAMMET File ASCII, in Separate PCRAMMET File
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Chemical Transformation
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Output Options
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Display Map of Shoreline, Sources, and Receptors
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Running the program
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Running the program
The hourly emission file is the only optional data.
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Case Study: Deepwater Horizon
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Summary
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Thank you!