OCD (Offshore and Coastal Dispersion Model)

A straight line Gaussian model developed to determine the impact of offshore emissions from point, area or line sources on the air quality of coastal regions. OCD incorporates overwater plume transport and dispersion as well as changes that occur as the plume crosses the shoreline. Hourly meteorological data are needed from both offshore and onshore locations.

Gaussian modeloffshore emissionscoastal regions

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Initial contribute: 2019-10-14

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Application-focused categoriesNatural-perspectiveAtmospheric regions

Detailed Description

English {{currentDetailLanguage}} English

Quoted from: https://www3.epa.gov/ttn/scram/userg/regmod/ocdugsup.pdf

        The Offshore and Coastal Dispersion (OCD) model has been developed to simulate the effect of offshore emissions from point, area, or line sources on the air quality of coastal regions. The OCD model was adapted from the EPA guideline model MPTER (EPA, 19801. Modifications were made to incorporate overwater plume transport and dispersion as well as changes that occur as the plume crosses the shoreline. Hourly meteorological data are needed from both overwater and overland locations. The overwater measurements include wind direction and speed, mixing height, overwater air temperature and relative humidity, and the sea surface temperature. Overland data include the standard EPA UNAMAP model requirements. Overwater and overland turbulence intensities are used by the model but are not mandatory. For overwater dispersion, the turbulence intensities are parameterized from boundary layer similarity relationships if they are not measured. 

        Specifications of emission characteristics and receptor locations are similar to the standard EPA UNAMAP models. Hourly emission rate, exit velocity, and stack gas temperature may also be specified. Up to 250 point sources, 5 area sources, or one line source and 180 receptors may be used. 

        Plume reflection off elevated terrain is calculated following the method proposed in the EPA TUPOS model (Turner et al., 1986). Plume inpaction on elevated terrain is calculated following procedures in the EPA RTDM (Rough Terrain Diffusion Model) (ERT, :1982). That is, if the plume is below the critical dividing streamline height (Hc), the plume impacts the terrain, and if the plume is above Hc, the plume flows up over the terrain. A revised platform downwash algorithm based on laboratory experiments is incorporated in OCD. Partial plume penetration into elevated inversions is treated using Briggs' model.

        A virtual source technique is used to change the rate of plume growth as the overwater plume intercepts the thermal internal boundary layer (TIBL) at the shoreline. The TIBL is assumed to be terrain following.

        The revised DCD model (Version 4) and the previous version of OCD (Version 3) are tested with measurements from four offshore tracer experiments. Considering the overall performance of the models, the OCD (Version 4) model is shown to be an improvement over the OCD (Version 3) model.

 

模型元数据

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US Environmental Protection Agency (2019). OCD (Offshore and Coastal Dispersion Model), Model Item, OpenGMS, https://geomodeling.njnu.edu.cn/modelItem/9920a3fa-150e-49f8-9307-86f3f858fcf9
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Initial contribute : 2019-10-14

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