In this document, the Environmental Protection Agency (EPA or Agency) is taking three separate but related actions. First, EPA is finalizing its determination that the Libby fine particulate matter (PM<INF>2.5</INF>) nonattainment area (Libby Area) is attaining the 1997 Annual PM<INF>2.5</INF> national ambient air quality standards (NAAQS or standard) based on 2014-2021 data. Secondly, EPA is finalizing approval of Montana's plan for maintaining the 1997 Annual PM<INF>2.5</INF> NAAQS (limited maintenance plan).

The Environmental Protection Agency (EPA) is finalizing particulate matter (PM) emission standards and test procedures applicable to certain classes of engines used by civil subsonic jet airplanes (engines with rated output of greater than 26.7 kilonewtons (kN)) to replace the existing smoke standard for those engines. The EPA is adopting these standards under our authority in the Clean Air Act (CAA).

On January 5, 2021, the United States Court of Appeals for the Tenth Circuit granted the Environmental Protection Agency's (EPA) motion for a voluntary remand without vacatur of two parts of an EPA 2020 final rule approving Colorado's infrastructure state implementation plan (SIP) submission for the 2015 8-hour ozone national ambient air quality standards (NAAQS) (2020 final rule). In this document, EPA is taking final action to approve those two remanded parts of the 2020 final rule.

The Environmental Protection Agency (EPA) is taking final action to approve a revision to North Dakota's State Implementation Plan (SIP) which it received on November 11, 2016. The revision was submitted by the North Dakota Department of Health (NDDH) in response to EPA's finding of substantial inadequacy and SIP call published on June 12, 2015 for a provision in the North Dakota SIP related to excess emissions during startup, shutdown, and malfunction (SSM) events.