CALPUFF 6.42 that could have been downloaded from our website for free. CALPUFF PRO.exe is the most common filename for this program's installer. The most popular versions among CALPUFF users are 6.4 and 5.2. The software lies within Education Tools, more precisely Science Tools. This free tool was originally produced by Exponent, Inc.
From the developer:
CALPUFF is a non-steady-state meteorological and air quality modeling system. The model has been adopted by the U.S. Environmental Protection Agency (USEPA) in its Guideline on Air Quality Models as the preferred model for assessing long-range transport of pollutants and their impacts on Federal Class I areas.
You may want to check out more software, such as Lakes Environmental CALPUFF View, which might be similar to CALPUFF.