For the purpose of dispersion modelling, the amount of pollutant released during a specified time can be measured or calculated. Measured emission rates are determined from actual samples taken from an emission point such as a stack. Calculated rates are determined using emission factors. In addition to information about pollutants released, the temperature and velocity of the emitted gas, as well as the stack height and diameter, are required.
An air emissions inventory is an accounting of air pollutant emissions for a given area. It is a database that contains information on sources and pollutants. In addition to air quality modelling, these inventories are used for air quality evaluations.