Frequently Asked Questions (FAQs) on ISCST3

 

Q: What source types does ISCST3 handle?

A: ISCST3 can be used to model impacts from point, volume, area, and open pit sources. Area sources can be defined as rectangular, circular or as an irregularly shaped polygon.

 

Q: Can ISCST3 be used for sources subject to building downwash influences?

A: The current regulatory version of ISCST3 includes the Huber-Snyder and Schulman-Scire building downwash algorithms. The current downwash algorithms in ISCST3 do not produce estimates for the cavity recirculation region directly downwind of the building. EPA is expected to propose the ISC-PRIME model as a replacement for the current ISCST3 at the upcoming 7th Modeling Conference. The ISC-PRIME model includes improved algorithms for handling building downwash influences, including algorithms for the building cavity region.

 

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 ISCST3 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: Is the ISCST3 model Y2K compliant?

A: Yes, the current version of ISCST3, dated 99155, includes modifications to make the model Y2K compliant. This was accomplished without requiring a change in the current formats of input meteorological data (i.e., to include 4-digit years) by using a date windowing technique.

 

Q: Where can I find the ISC3 Event Model, ISCEV3?

A: The current version of ISCST3, dated 99155, incorporates the EVENT processing routines that were formerly available in a separate program called ISCEV3. ISCST3 can now be run in either the normal processing mode, or in the event processing mode, depending on the inputs provided. Incorporating the event processing routines into the ISCST3 model simplifies and streamlines future maintenance and upgrades of the ISCST3 model.

 

Q: What meteorological data formats does PCRAMMET process?

A: PCRAMMET can process the following data formats:

Hourly Surface Observations

CD-144 – 80-character card image format formerly available from the National Climatic Data Center (NCDC)

SCRAM – available from EPA’s SCRAM web site

SAMSON – data retrieved from the Solar and Meteorological Surface Observation Network CD-ROM

HUSWO – data retrieved from the Hourly U.S. Weather Observations CD-ROM

Upper Air Soundings

SCRAM – twice-daily mixing height data available from SCRAM

PCRAMMET does not support on-site meteorological observations directly. For processing of on-site data, the Meteorological Processor for Regulatory Models (MPRM) should be used.

 

For more information about ISC3, or to submit a question not answered here, contact PES at Roger.Brode@pes.com.