Approval and Promulgation of Air Quality Implementation Plans; State of Montana; Missoula PM10 Nonattainment Area Limited Maintenance Plan and Redesignation Request

The Environmental Protection Agency (EPA) is approving the Limited Maintenance Plan (LMP), submitted by the State of Montana to the EPA on August 3, 2016, for the Missoula moderate particulate matter with an aerodynamic diameter less than or equal to a nominal 10 micrometers (PM<INF>10</INF>) nonattainment area (Missoula NAA) and concurrently redesignating the Missoula NAA to attainment of the 24- hour PM<INF>10</INF> National Ambient Air Quality Standard (NAAQS). In order to approve the LMP and redesignation, the EPA is determining that the Missoula NAA has attained the 1987 24-hour PM<INF>10</INF> NAAQS of 150 [micro]g/m\3\. This determination is based upon monitored air quality data for the PM<INF>10</INF> NAAQS during the years 2015-2017. The EPA is also approving the Missoula LMP as meeting the appropriate transportation conformity requirements. Lastly, the EPA is approving certain rule revisions the Missoula City-County Air Pollution Control Program submitted on August 3, 2016, and August 22, 2018.