A technique for predicting what concentration of a pollutant will occur at a particular place. It relies on being given information about the source of a pollutant (either assumed or measured), and then assuming that it is dispersed in a particular way that can be described mathematically. The more complex models are often run on computers. Models can be reasonably accurate when describing the dispersion of a single pollutant from a single point source. Other models, even sophisticated ones, can have large margins of error (± 100% or worse).