ISC3 (Industrial Source Complex, Version 3) is a steady-state Gaussian plume model which can be used to assess pollutant concentrations from a wide variety of sources associated with an industrial complex. For many years it has been the US-EPA preferred/recommended air dispersion model for modelling the impact of ground level and elevated industrial sources on flat or moderately complex terrain. Starting from December 2006 it has been replaced by AERMOD within such list. ISC3 now belongs to the list of the US-EPA alternative models (i.e. models that can be used in regulatory applications with case-by-case justification).

ISC3 operates in both short-term (ISCST3) and long-term (ISCLT3) modes. The meteorological input data needed for the two operating modes are completely different. The minimum set of meteorological data needed by ISCST3 for each hour of simulation is composed by: flow vector (which is the opposite of wind direction), wind speed, temperature, Pasquill Gifford stability class, rural mixing height and urban mixing height. Additional variables are needed if dry and/or wet depositions must be calculated, they are: friction velocity, Monin Obukhov length, surface roughness length, precipitation rate and precipitation type. The meteorological data needed by ISCLT3 is a joint frequency distribution of wind speed and wind direction by stability category, which is known as STAR (STability ARray).

The PRIME (Plume Rise Model Enhancement) algorithms – the next generation building downwash paradigm – have been incorporated into the ISCST3 source code and the new model has been called ISC-PRIME.