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

Abstract

SummaryThe 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 full range of potential particle properties, 3) the incorporation of particle surface retention/rebound processes, and 4) the development of dry deposition formulations applicable to urban areas. Also, to improve dry deposition modeling capabilities, atmospheric dispersion models in which the dry deposition formulations are imbedded need better source-term plume initialization and improved in-plume treatment of particle growth processes.Dry deposition formulations used in current models are largely inapplicable to the complex urban environment. An improved capability is urgently needed to provide surface-specific information to assess local-exposure hazard levels in both urban and non-urban areas on roads, buildings, crops, rivers, etc.A model improvement plan is developed with a near-term and far-term component. Despite some conceptual limitations, the current formulations for particle deposition based on a resistance approach have proven to be reasonable dry deposition simulations. For many models with inadequate dry deposition formulations, adding or improving a resistance approach will be the desirable near-term update. Resistance models, however, are i...

A new parameterization of particle dry deposition over rough surfaces

“…Particle dry deposition, the removal of particles from the atmosphere to the surface in absence of precipitation (Seinfeld and Pandis, 2006), can be divided into several sub-processes, including turbulence diffusion, surface collection and gravitational settling (Droppo, 2006). The inferential method is widely used to estimate particle deposition flux in terms of particle concentration and deposition velocity (or its inverse, the resistance) (Sehmel, 1980;Slinn, 1982;Hicks et al, 1987;Wesely and Hicks, 2000;Raupach et al, 2001;Zhang et al, 2001;Petroff and Zhang, 2010;Seinfeld and Pandis, 2006;Kouznetsov and Sofiev, 2012).…”

Deposition Velocity Methods For DOE Site Safety Analyses

“…Phoretic mechanisms are the result of gradients in the surrounding environment that affect particle motion. Such mechanisms influence the deposition rates of particles small enough to have high ion mobility or to be impacted by molecular collisions (Droppo, 2006). The magnitudes of phoretic forces are small compared to the deposition processes discussed above and are therefore ignored by the majority of dry deposition models 17 .…”

Improvement and Impacts of Forest Canopy Parameters on Noah-MP Land Surface Model from UAV-Based Photogrammetry

“…The parameterizations about the forest canopy structure of land surface models that are commonly coupled in meteorological or climate simulations are listed in Table 1 [9][10][11][12][13][14][15]. Different parameterization schemes divide the canopy into one layer, two layers or multiple layers to calculate the energy decomposition or radiative transfer in the canopy [16][17][18][19]. For the calculation of the atmospheric dynamic process, the current land surface models that have been widely used in climate and hydrology researches, such as simple biosphere model (SiB4) and biosphere atmosphere transfer scheme (BATS), are based on the measured empirical wind speed profile in the canopy and provide an empirical solution to calculate the turbulent exchange in the canopy [20,21].…”