LONGZ is designed to calculate the long-term and SHORTZ is designed to calculate the short-term pollutant concentration produced at a large number of receptors by emissions from multiple stack, building, and area sources. LONGZ uses statistical wind summaries to calculate long-term (seasonal or annual) average concentrations. SHORTZ uses sequential short term (usually hourly) meteorological inputs to calculate concentrations for averaging times ranging from 1 hour to 1 year. The models are applicable in areas of both flat and complex terrain, including areas where terrain elevations exceed stack-top elevations. The programs require random-access mass storage capability. Software Description: The software is written in the FORTRAN programming language for implementation on an IBM model 3090 computer. The model is distributed on a 5 1/4-inch IBM/PC-compatible diskette. Data is in compressed format but a dearchive utility is included.