4.10 SOURCE MASS BUDGET


        The emission of a constituent will deplete the inventory of that constituent at the site. With one exception, the depletion of the mass by a gaseous emission in the inventory of an area source is assumed to proportionally reduce the emission rate. The exception is for the case of a landfill treatment/old spill volatilization computation where a constant emission rate is assumed with a linear reduction in the inventory. The depletion of mass for particulate emissions also does not change the emission rate.

For sites where the inventory is known, or can be estimated, the proportional depletion is computed using

(67)


where
        In the current MEPAS user interface implementation, the default is to assume that source depletion occurs for all gaseous and particulate constituents in an area source case for which inventories are input. The investigator has the option of defining an average emission rate for a 70-year period with no inventory, or an initial emission rate with the inventory. The former requires that the investigator externally account for mass depletion, and the latter allows use of MEPAS formulations to account for the source depletion.