text: Two parts of the controversy over calculating PTE are the choice of a base year and the expected future utilization of capacity. Many plants run at less than full capacity and maintain their emissions below caps put in place by other programs (e.g., caps on SOx under the Title IV acid rain program and caps on other pollutants under the National Ambient Air Quality Standards Program) in order to have the flexibility to increase or alter production on short notice without having to go through the permitting process. If emissions in a year of historically low utilization are used as the base for determining whether future emissions are significant, then more modifications become subject to NSR.