Improved Formulations for Air-Surface Exchanges Related to National Security Needs: Dry Deposition Models

DISCLAIMER This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor Battelle Memorial Institute, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof, or Battelle Memorial Institute. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof. Summary The Department of Homeland Security and others rely on results from atmospheric dispersion models for threat evaluation, event management, and post-event analyses. The ability to simulate dry deposition rates is a crucial part of our emergency preparedness capabilities. Deposited materials pose potential hazards from radioactive shine, inhalation, and ingestion pathways. A reliable characterization of these potential exposures is critical for management and mitigation of these hazards. A review was conducted of the current status of dry deposition formulations used in these atmospheric dispersion models. The formulations for dry deposition of particulate materials considered an event such as a radiological attack involving a Radiological Detonation Device (RDD). The results of this effort are applicable to current emergency preparedness capabilities, such as are deployed in the Interagency Modeling and Atmospheric Assessment Center (IMAAC), other similar national/regional emergency response systems, and stand-alone emergency response models. The review concludes that dry deposition formulations need to consider the full range of particle sizes, including: 1) the accumulation mode range (0.1 to 1 micron in diameter) and its minimum deposition velocity, 2) smaller particles (less than 0.01 micron diameter) deposited mainly by molecular diffusion, 3) 10 to 50 micron diameter particles deposited mainly by impaction and gravitational settling, and 4) larger particles (greater than 100 micron diameter) deposited mainly by gravitational settling. The effects of the local turbulence intensity, particle characteristics, and surface element properties must also be addressed in the formulations. Specific improvements recommended for dry deposition formulations are 1) the capability of simulating near-field dry deposition patterns, 2) the capability of addressing the …