Abstract Description: In 2019 the Department of Interior’s Bureau of Ocean Energy Management (BOEM) and the U.S. Environmental Protection Agency (EPA) began an Interagency Agreement (IA) to research and eventually replace the Overwater Coastal Dispersion (OCD) model with the American Meteorological Society and EPA Regulatory Model (AERMOD) for overwater applications. The main areas of attention have been the addition of platform downwash and shoreline fumigation to the AERMOD model.
Platform downwash leads to the mixing of platform emissions toward the sea-surface, increasing ambient air impacts for areas surrounding these platforms. An ALPHA version of the platform downwash algorithm was integrated into AERMOD in 2022. During implementation, initial model evaluations were conducted but showed discrepancies between modeled and measured concentrations from wind tunnel studies. Further work has been conducted to improve model algorithms with emphasis on improving model evaluations.
Overwater emission sources can impact ground-level ambient air on shore, as the shoreline fumigation phenomena entrains emission plumes from a stable overwater boundary layer into a turbulent overland boundary layer and mixes pollutants toward the ground. The shoreline fumigation algorithm from OCD was selected to be implemented in AERMOD Areas of concern for implementation include overwater meteorology and depiction of the shoreline. Implementation has begun and is ongoing.
Adding platform downwash and shoreline fumigation algorithms to the AERMOD modeling system will improve dispersion modeling for coastal regions with the capability to more accurately model near-shore and off-shore sources. This work outlines the necessary steps and current progress toward incorporating these algorithms into the AERMOD modeling system, and progress toward eventual replacement of the OCD model for near- and off-shore emission sources.
