Screen View is a Windows interface to the U.S. EPA screening model, Screen3. Screen View allows you to obtain ground-level pollutant concentration estimates for a single source. You can use Screen View, for example, to analyze the worst case scenarios for air pollutant concentrations.

The following are some of the features of Screen View:

• Screen View has an integrated modeling environment: intuitive data input, model run, and full featured post-processing (XY plotting). The graphical output can be directly pasted into your favorite Windows word processor.
• You can easily change the units between Metric and English at any time for each entry field.
• The program checks all entry fields for valid data which will save you time by preventing inappropriate entries that cause modeling headaches.
• Before running your project, a report of all options selected along with a list of any missing information is displayed on the screen.
• Screen View comes with a context-sensitive Help that really helps, which provides you with a clear explanation of modeling requirements.

The Screen View model can perform the following:

• Estimates maximum ground-level concentrations and the distance to the maximum.
• Incorporates the effects of building downwash on the maximum concentrations for both the near wake and far wake regions. Estimating concentrations due to inversion breakup and shoreline fumigation.
• Calculates the maximum concentration at any number of user-specified distances in flat or elevated simple terrain, including distances out to 100 km for long-range transport.
• Examines a full range of meteorological conditions including all stability classes and wind speeds to find maximum impacts.

Screen View contains all the available options of the U.S. EPA model in addition to the following:

• Screen View has an integrated modeling environment: intuitive data input, model execution, and full-featured post-processing (XY plotting).
• For each source, the data is input in two windows, making it easy to have a complete view of all the information.
• You can easily change between Metric and English units, at any time, by clicking the unit button located beside each entry field.
• The program checks valid ranges for all entry fields, which will save time by preventing incorrect entries.
• Before running your project, Screen View displays a report of all options selected along with a list of any missing information.

A complete graphics package is also available within Screen View. Screen View comes with a context-sensitive "Help that really helps" which includes the basic explanations for each option or command and incorporates many sections of EPA's most-used documentation guides to help you better understand the modeling process.

Source Data: You can model one source at a time which can be a point, flare, area, or volume source. Source parameters including emission rate, physical stack height, stack gas exit velocity, etc., are needed. Some examples of the sources you can model are:

• Point: stacks, soil vapor extraction vents.
• Area: landfills, lagoons, VOCs emanating from a SuperFund site.
• Flares: burning gas from a landfill gas collection.
• Volume: leaking gases from a plant, conveyor belts.

Source Input

• Receptor Data: Receptor distances from the source are needed. If modeling on elevated terrain, the terrain height at the receptor location should be specified.
• Meteorological Data: No need for meteorological data input. The model automatically examines a full range of meteorological conditions, including all stability classes and wind speeds to find maximum impacts.
  

Screen Input Options

The following are the options available for each type of source: Point, Flare, Area, and Volume.

Building Downwash Option:
The building downwash option is only applicable to Point and Flare source types. Downwash occurs when the aerodynamic turbulence induced by nearby buildings cause a pollutant emitted from an elevated source to be mixed rapidly toward the ground (downwash), resulting in higher ground-level concentrations.

Complex Terrain Option:
The complex terrain option is only applicable to Point and Flare source types.

The complex terrain option of Screen calculates maximum 24-hour concentrations for terrain elevations exceeding stack height.

Simple Terrain Option:
When modeling simple terrain, you are given the option of modeling either:

• Simple Flat Terrain: where terrain heights are assumed not to exceed stack base elevation. If this option is used, terrain height is considered to be 0.0 m.
• Simple Elevated Terrain (Not Available for Area Sources): where terrain heights exceed stack base but are below stack height. If this option is used, the terrain height above stack base should be specified. If terrain heights above physical stack height are entered, Screen View gives a warning message and the user has to reenter a valid height value.

To model simple elevated or simple flat terrain, you can choose either or both of the distance options (Automated Distances or Discrete Distances).

Automated Distances Option:
The Automated Distances option gives the user the option of using a preselected array of 50 distances ranging from 100 m out to 50,000 m (50 km) using the following increments.

For the Automated Distances option, the Screen model calculates the maximum concentration across a range of meteorological conditions for the minimum distance given. Screen then computes the concentration for each distance in the array larger than the minimum and less than or equal to the maximum. Screen also uses an iteration routine to determine the maximum value associated with that distance to the nearest meter.

Discrete Distances Option:
The Discrete Distances option allows the user to find the maximum impact at specific locations of interest, such as nearby residences, hospitals, or schools, and may also be used for long-range transport estimates out to 100 km. Any number of distances (equal or greater than 1.0 m) can be input and the maximum concentration for each distance will be calculated.

Choice of Meteorology :
Three choices of meteorology are available when modeling with Simple Terrain screening:

Full Meteorology (All Stability Classes and Wind Speeds): Screen will examine all six stability classes (five for urban sources) and their associated wind speeds. Screen examines a range of stability classes and wind speeds to identify the "worst case" meteorological conditions, i.e., the combination of wind speed and stability that results in the maximum ground level concentrations.

Input Single Stability Class: You have to select the stability class to be used (A through F) from the stability list. Screen will then examine a range of wind speeds for that stability class only.

Input Single Stability Class and Wind Speed: You have to select the stability class and input the 10-meter wind speed to be used. Screen will examine only that particular stability class and wind speed. To help you on the choice of the wind speed, Screen View gives the wind speed range for each stability class, which is printed at the bottom of the wind speed text box.

Generally the Full Meteorology option should be selected. The other two options were originally included in the Screen model for testing purposes only, but may be useful when particular meteorological conditions are of concern.

Fumigation Option:
Fumigation occurs when a plume that was originally emitted into a stable layer is mixed rapidly to ground level when unstable air below the plume reaches plume level.

The Fumigation option is only available for Point and Flare source types if :

• The Rural dispersion coefficient was selected (for rural inland sites), and
• The Stack Height >= 10 meters (see Note 1 in case of Flare type source)

After you run your project, Screen View generates a series of plots (distance versus concentration) using the output file generated by EPA's Screen3 model. If your project ran successfully, you can have access to the "Graphic Results" Window and view these plots.

In the "Graphic Results" Window, a list of the available plots can be found on the drop-down list box located below the toolbar menu. Many options are available to the user to enhance the appearance of the plots generated from the Screen3 output file. You can have access to these options through the Options Buttons located on the right-hand-side of the "Graphic Results" Window.

• Pentium
• At least 20 MB of available hard disk space and 16 MB of RAM
• Windows versions 95/98/2000/NT