Air Dispersion Modeling

SoftWright is pleased to assist you in providing topographic elevation data that can be supplied to popular air dispersion modeling software.

Many of the air dispersion modeling software programs require the input of terrain data. For many years consultants have been forced to manually plot receptor grid locations on maps and read the topography elevations from the maps. They would then generate computer files containing this information. This file is then supplied as input to the air dispersion modeling software. This entire time-intensive process can be streamlined by using digitized maps (DEMs – digital elevation models).

Typically, a study in a region is first done by identifying a specific location and evaluating out to a distance of approximately 50 km from that location with receptor grid spacing at a course setting such as 1000 meters. When the impact area has been located, the study is rerun in a smaller area with the receptor grid spacing tightened up to more accurately display the level of contamination in the impact area. This type of iterative process is repeated over smaller geographic areas and with tighter receptor grid spacing until contaminant levels are ascertained.

In addition to software necessary to do this modeling, generally two other things are required if terrain data is necessary for your model. First of all you must acquire DEMs for the geographic region where you need to perform the study. These can be supplied in several resolutions and numerous file formats. Many of the air dispersion modeling software packages do not read the DEMs directly, but rely on an intermediate software package to create an ASCII data file containing the actual input information for the air dispersion modeling software. These files typically contain details calculated from input provided by you about the area for your study and receptor spacing.

SoftWright can supply various resolutions of DEMs for the entire world. These digital elevation models can be purchased by small regions, states, provinces, countries or the entire world. SoftWright also offers two software packages one called the Basic Mapping Package, which sells for $950 plus shipping, and the other called QuickPath ($199) both of which prepare ASCII data files in the event your air dispersion modeling software cannot read USGS ASCII DEM files directly. You can download a complete working demo of QuickPath by clicking here. (This file is approximately 32MB.) There is no time-frame limitation on this demo, but it will be fully functional only within the area around Denver, Colorado. Should you purchase it and topographic data in your region, we can convert your demo version to a working copy of the software. With this demo you can create files that you can use to import into your application software to assure you of file compatibility. You specify the geographic perimeter of the region to include, the system of coordinates (latitude, longtitude, UTM), the vertical elevation units (feet, meters) and then you can specify output file format (xyz ASCII, surfer grid, Lakes Environmental, Gridzo), within the area provided in the demo.

Click here to download a sample output file (to decompress the file after download, execute it from explore or from the run command) from the Basic Mapping Package which provides the format that can be used by the air dispersion modeling software listed below. This same format can be created with QuickPath. This particular sample file contains the elevation data for a region in metropolitan Denver, Colorado that is a region 2 km in all directions from the following UTM coordinates (UTM zone 13, easting – 500,000, northing – 4,390,761.55) with a receptor spacing of 0.1 km with elevation in meters above mean sea level. The contents of this file is x,y,z. The x is easting in km; y is northing in km; and z is elevation at that particular location in meters. The software allows you to specify any central point, the distance out from that location and the spacing of the actual receptor grid locations. The Basic Mapping Package can also work in latitude-longitude coordinate system, as well as in both British and Metric units.

If your software can read USGS ASCII file format and you are only interested in preparing studies within the continental United States, you will need to specify USGS ASCII file format when you order data from SoftWright and you will not need the Basic Mapping Package. However, should you do work outside the continental United States, the USGS formats are not available. In that case you would need the Basic Mapping Package and need to verify that you can read the above sample input file in your air dispersion modeling software. If it cannot be directly read by your modeling software, the file can generally be easily modified to conform to the file format by using spreadsheet software. SoftWright is also pleased to offer complete file format details to any software developer who wishes to directly read our DEMs.

If your presentation can benefit from the use of tools to plot the topography in three dimensions, we offer an excellent software tool, Surfer, which can prepare these graphics using grid files that can also be prepared directly from the Basic Mapping Package. You can also plot results from your air dispersion modeling software onto these three-dimensional maps showing the concentration of pollutants on the surface of the topography.

We can refer you to several organizations who provide air dispersion modeling software or to those who can do the actual air dispersion modeling studies for you. Again, to actually use these programs, you will need both the DEMs and a program into which you put the geographic boundaries for your study and information about the bin size and receptor grid spacing that you specify.

Organizations who supply air dispersion modeling software:

Lakes Environmental Software
Phone: 519-746-6157
Fax: 519-746-0793
http://www.lakes-environmental.com/index.html
info@lakes-environmental.com

US Environmental Protection Agency
http://www.epa.gov/ttn/scram
http://www.epa.gov/epahome/datatool.htm

Other Links of Interest
Information on US EPA Models
http://www.lakes-environmental.com/lakeepa1.html
http://www.epa.gov

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