Dispersion models
Dispersion models
1. Meteorological Modeling Tools
Many emergency response situations require detailed analyses and forecasts relevant to local conditions. National or International meteorological centres are not always in a position to provide such support. In these situations, it is recommended that local centres generate their own forecasts using public domain meso-scale meteorological models. As an example, global forecast data in GRIB format are available from NOAA to provide initial and boundary conditions.
2. Dispersion Modeling Tools
In a conceptually similar framework to the meteorological modeling problem, dispersion models, either source code or executables, can be obtained to support a local response to an emergency. Such a system does not rely on communications with a remote centre.
2.1 The NOAA HYSPLIT model
A 3-d Lagrangian particle/puff model that uses meteorological model output fields as input for the dispersion calculation. It can be customized to support a variety of different simulations. Interface programs are available to process MM5, ETA, RAMS, or ECMWF model output fields.
2.2 The NOAA CAMEO Software Suite
Provided by NOAA’s Office of Response and Restoration, it consists of a chemical database linked with a straight line Gaussian model for very short-range applications to estimate threat zones associated with hazardous chemical releases, including toxic gas clouds, fires, and explosions.
2.3 The EPA Air Quality Models Web page provides information on dispersion modeling and access to models and related databases.
2.4 See also the following:
FLEXPART (FLEXible PARTicle dispersion model)
SCIPUFF (Second-order Closure Integrated Puff)
3. Application of Generic Models to Specific Emergencies
Most dispersion models are very generic in that the pollutant is assumed to passively transported by the wind. They are customized for specific applications by configuring the geometry of the source term, the specific characteristics of the pollutant such as its transformation and removal. Some examples follow:
3.1 Volcanic Ash
Many of the models used by the RSMCs are also configured for the modelling of volcanic ash transport, dispersion and deposition and are used by Volcanic Ash Advisory Centres. As examples, see NOAA’s HYSPLIT for volcanic ash modelling and the Meterorological Service of Canada's modelling of the Okmok and Kasatochi 2008 eruptions.
The typical configuration focuses mainly finer particles that are normally transported to greater distances and are more of an aviation hazard. For more local concerns, perhaps health or deposition issues, one would need more information about the source structure and characteristics. These tend to be very volcano and eruption specific and lend themselves easily to local solutions, an example of which is shown over Hawaii.
3.2 Chemical Accidents
As noted earlier, NOAA’s model for chemical accidents, usually applied over very short distances, is linked to the CAMEO Chemicals database. As with many of these types of scenarios, accurate prediction of the consequences of the hazard depends on how accurately the source can be described. Fortunately there are certain limitations to the problem, such as the maximum capacity of a chemical tanker. More information on available databases and software for chemical emergencies are available from the US EPA. Chemical database information can easily be incorporated into any dispersion model. However, chemical transformations from one species to another are a more difficult issue. Guidance for dispersion modeling of toxic pollutants in urban areas is also available.
3.3 Wild-land Fires
The issue of wild-land fires and smoke is receiving considerable attention by various meteorological centres. An example of the current NOAA forecast for the United States can be found here. The key to many of these systems is linking them to a detection system for fire locations, such as NOAA's Hazard Mapping System. More information is available on the various components, such as fire detection methods, and an overview of the hazard system. An example of an application over Argentina is shown here as well as the modelling of the stratospheric injection of forest fire smoke from a pyrocumulonimbus event in Canada (part I and Part II).
3.4 Biological Emergencies
One common biological application is related to the spread of plant diseases and the spread of pollen. The transport of animal diseases is also modeled. For example, for the spread of the foot-and-mouth disease. The modelling of these can be more complicated than they appear at first due to interactions between the meteorology and the source term.
3.5 Sand and Dust Storms
Experimental sand and dust storms forecast advisories are available for Northern Africa – Middle East – Europe and for the Asian Region. Examples of aerosol observations and forecasts can be found at the NRL Aerosol page.
4. End-User Training Issues
4.1 Generic
Although it is easy to direct interested parties to the Internet to find the necessary resources so that they can devise local solutions to local problems, it is also recognized that there is a also a certain level of expertise and training required for implementation of these solutions. On-line help and training is continuously expanding. For instance, the MetEd - COMET program has on-line training for Dispersion Basics and HYSPLIT Applications for Emergency Decision Support. There is also a more specific component for CAMEO - ALOHA. Some more general information is available from the Air Pollution Training Institute.
4.2 HYSPLIT
The HYSPLIT model contains on-line help as well as contextual help through the menus of the stand-alone PC version. In addition, a training workshop is available. A Spanish version of the HYSPLIT model Web site is also available on-line.
5. Bibliography
Arya, S. Pal, 1999, Air pollution meteorology and dispersion, Oxford University Press, ISBN 0195073983, 310 p.
Hanna, S.R., G.A. Briggs, and R.P. Hosker, Jr., 1982, Handbook on atmospheric diffusion, US Dept. of Energy DOE/TIC -22800, NTIS, Springfield, VA., 102p.
Pasquill, F. and F.B. Smith, 1983, Atmospheric diffusion, 3rd Ed, John Wiley & Sons, ISBN 0853124264, 437 p.
Jacobson, M.Z., 2005, Fundamentals of atmospheric modeling, 2nd Ed., Cambridge University Press, ISBN 0521548659, 813 p.
Zannetti, Paolo, 1990, Air pollution modeling: theories, computational methods, and available software. Computational Mechanics, ISBN 1853121002, 444 p.
Updated 2 May 2014