CALPUFF is a non-steady-state, integrated modeling system used for a wide variety of air quality modeling studies, including toxic pollutant deposition, near-field impacts from point, line, area, and volume sources, forest fire impacts, visibility assessments, and long range transport studies. The model has been adopted by the U.S. Environmental Protection Agency in its Guideline on Air Quality Models as the preferred model for assessing the long range transport of air pollutants.