pollutant balance
pollutant budget

Lean-burn engines do not work well with modern 3-way catalytic converter-which require a pollutant balance at the exhaust port so they can carry out oxidation and reduction reactions-so most modern engines run at or near the stoichiometric point.

Heat and pollutant budgets for streams and holding ponds in the Markham area (1993)

EPA has described TMDLs as establishing a pollutant budget then allocating portions of the overall budget to the pollutant's sources.