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Offshore and Coastal Dispersion (OCD) Model

Heather Groce. Offshore and Coastal Dispersion (OCD) Model. Outline. Introduction Methodology and Applications Installation Use Case Study Summary. Introduction to OCD. Simulates offshore emissions from point, area, or line sources to receptors on land or water

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Offshore and Coastal Dispersion (OCD) Model

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  1. Heather Groce Offshore and Coastal Dispersion (OCD) Model

  2. Outline • Introduction • Methodology and Applications • Installation • Use • Case Study • Summary

  3. 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?

  4. 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

  5. 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

  6. 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

  7. Applications

  8. 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)

  9. 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

  10. Some Definitions

  11. Installation • Code can be downloaded from the EPA’s Preferred/Recommended Models webpage • User-friendly interface http://www.epa.gov/ttn/scram/dispersion_prefrec.htm

  12. Using OCD

  13. Starting a New Model

  14. Input Menu Nine input windows:

  15. Run Information

  16. Model Domain

  17. Sources • New Inputs: • Stack angle from the vertical • Height of stack top above its base* • Height of building at or near stack base

  18. Dispersion

  19. Receptors

  20. Types of Receptors • Discrete • Polar • Cartesian

  21. Meteorology

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

  23. Chemical Transformation

  24. Output Options

  25. Display Map of Shoreline, Sources, and Receptors

  26. Running the program

  27. Running the program • The hourly emission file is the only optional data.

  28. Case Study: Deepwater Horizon

  29. Summary

  30. Thank you!

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