The Environmental Protection Agency (EPA or Agency) is finalizing the determination that the Sullivan County, Tennessee, sulfur dioxide (SO<INF>2</INF>) nonattainment area (hereinafter referred to as ``the Sullivan County Area'' or ``Area'') failed to attain the 2010 1-hour SO<INF>2</INF> primary National Ambient Air Quality Standard (NAAQS or standard) by the applicable attainment date of October 4, 2018, based upon a weight of evidence analysis of available quality-assured and certified SO<INF>2</INF> ambient air monitoring data and SO<INF>2</INF> emissions data from January 2015 through December 2017. As a result of this determination, the State of Tennessee is required to submit by April 5, 2023, revisions to the Tennessee State Implementation Plan (SIP) that, among other things, provide for the attainment of the SO<INF>2</INF> NAAQS in the Sullivan County Area as expeditiously as practicable but no later than April 5, 2027.