[ISO 16814:2008, 3.12]:ratio of the rate at which an air pollutant is entitled as a result of some activity, to the rate of that activity.NOTE 1 Adapted from ISO 4225:1994 [46].NOTE 2 The point or area from which the discharge takes place is called the “source”. The term is used to describe the discharge and the rate of discharge. The term can also be applied to noise, heat, etc.