Frequently Asked Questions (FAQs) on SCREEN3

 

Q: What source types does SCREEN3 handle?

A: SCREEN3 can be used to model impacts from point, flare, volume, and area sources.

 

Q: I am modeling a source with building downwash, and after removing the rain cap to increase plume rise, the concentrations increase rather than decrease. Why does this happen?

A: The building downwash algorithms in the current version of SCREEN3 include enhanced lateral dispersion (i.e., increased F y) when the plume height due to momentum rise at two building heights downwind (i.e., the "wake plume height") is less than or equal to 1.2 times the building height. If the wake plume height is greater than 1.2 building heights, then there is no enhanced lateral dispersion. Removing the rain cap on a stack will increase the plume momentum, and therefore the wake plume height. This may cause the wake plume height to exceed the 1.2 building height limit for lateral enhancement. By eliminating enhanced lateral dispersion, the ground-level concentration may increase, even though the plume height has increased. You may want to try PES’ Heff On-line utility program, which will calculate the wake plume height for a range of meteorological conditions, and indicate which conditions will subject the plume to building downwash influences, and will also indicate whether enhanced lateral dispersion will apply.

 

Q: Can the SCREEN3 model be run in a batch mode?

A: The SCREEN3 model can be run in a batch mode by redirecting the input from a separate data file as follows:

C:\>SCREEN3 <input.dat

where "input.dat" is the input data file. The SCREEN3 model automatically creates a data file of inputs for a particular model run in a file called SCREEN.DAT.

 

Q: How do I input the meteorology for SCREEN3?

A: Unlike ISCST3, the SCREEN3 model does not use hourly meteorological data. Instead, the user can select one of the following options:

    1. Full Meteorology – model uses a predefined matrix of meteorological conditions that references all stability classes (A through F) and associated wind speeds, where the maximum wind speed is stability-dependent;
    2. Single Stability Class – user selects a single stability category, and the model automatically examines all wind speeds appropriate for that category; or
    3. Single Stability Class and Wind Speed – user selects a single stability category and wind speed combination.

For routine application of the SCREEN3 model, the Full Meteorology option should be used.

For more information about SCREEN3, try running SCREEN3 On-line, or to submit a question not answered here, contact PES at Roger.Brode@pes.com.