ISCST3 Tech Guide
6.1.7 The Decay Term
The Decay Term in Equation (1-1) is a simple method of accounting for pollutant removal by physical or chemical processes. It is of the form:
For example, if T1/2 is the pollutant half life in seconds, the user can obtain R from the relationship:
The default value for R is zero. That is, decay is not considered in the model calculations unless R is specified. However, a decay half life of 4 hours (R = 0.0000481 s-1) is automatically assigned for SO2 when modeled in the urban mode.