This bill amends the Clean Air Act to clarify when physical or operational changes at stationary sources constitute a "modification" or "construction" under New Source Review permitting requirements. It redefines an emission increase for modification purposes, specifying that it occurs only if the maximum hourly emission rate achievable after a change is higher than the maximum hourly rate during any hour in the preceding 10 years. The bill also exempts certain projects from being considered a modification, including those designed to reduce emissions per unit of production or to restore, maintain, or improve reliability or safety of operations. These exemptions apply unless the Administrator determines an increase in the maximum achievable hourly emission rate would cause an adverse effect on human health or the environment. For Prevention of Significant Deterioration (PSD) and nonattainment areas, the bill clarifies that a change at a major emitting facility is not considered construction or a modification if it does not result in a significant emissions increase or a significant net emissions increase in annual actual emissions . This aims to streamline the permitting process by narrowing the scope of changes that trigger New Source Review requirements.