The Environmental Protection Agency (EPA) is taking final action to approve, or conditionally approve, all or portions of a state implementation plan (SIP) revision submitted by the State of California to meet Clean Air Act (CAA or ``Act'') requirements for the 2008 8-hour ozone national ambient air quality standards (NAAQS or ``standards'') in the Nevada County (Western part), California ozone nonattainment area (``Western Nevada County''). The SIP revision is the ``Ozone Attainment Plan, Western Nevada County, State Implementation Plan for the 2008 Primary Federal 8-Hour Ozone Standard of .075 ppm'' (``2018 Western Nevada County Ozone Plan'' or ``Plan''). The 2018 Western Nevada County Ozone Plan addresses the ``Serious'' nonattainment area requirements for the 2008 ozone NAAQS, including the requirements for emissions inventories, attainment demonstration, reasonable further progress, reasonably available control measures, and contingency measures, among others; and establishes motor vehicle emissions budgets. The EPA is approving the 2018 Western Nevada County Ozone Plan as meeting all the applicable ozone nonattainment area requirements except for the contingency measure requirement, which the EPA is conditionally approving.