Offshore and Coastal Dispersion (OCD) ModelHeather Groce

Outline

I. IntroductionII. Methodology and ApplicationsIII. InstallationIV. UseV. Case StudyVI. Summary

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?

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

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

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

Applications

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)

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

Some Definitions

Installation

Code can be downloaded from the EPA’s Preferred/Recommended Models webpage

User-friendly interfacehttp://www.epa.gov/ttn/scram/dispersion_prefrec.htm

Using OCD

Starting a New Model

Input Menu

Nine input windows:

Run Information

Model Domain

Sources

New Inputs:• Stack angle

from the vertical

• Height of stack top above its base*

• Height of building at or near stack base

Dispersion

Receptors

Types of Receptors

Discrete Polar Cartesian

Meteorology

Sources of Meteorological Data ASCII, included in Control File Binary, in Separate PCRAMMET File ASCII, in Separate PCRAMMET File

Chemical Transformation

Output Options

Display Map of Shoreline, Sources, and Receptors

Running the program

Running the program

The hourly emission file is the only optional data.

Case Study: Deepwater Horizon

Summary

Thank you!