Through this supplemental notice of proposed rulemaking (``supplemental proposal'' or ``SNPRM''), the Environmental Protection Agency (EPA) is seeking public comment on the Agency's additional and clarified technical rationale related to the proposed approval of Tennessee's February 26, 2020, state implementation plan (SIP) revisions requesting the removal of Tennessee's motor vehicle inspection and maintenance (I/M) program requirements for Davidson, Sumner, Rutherford, Williamson, and Wilson Counties in Tennessee (also known as the Middle Tennessee Area) and Hamilton County (also known as the Chattanooga Area), from the federally-approved SIP. Specifically, EPA proposes to affirm that the Hamilton County and Middle Tennessee areas would continue to attain and maintain the national ambient air quality standards (NAAQS or standards) after removal of the I/M program, and to rely on an emissions inventory comparison to inform its determination that both areas would continue to attain and maintain the ozone and carbon monoxide (CO) NAAQS. EPA is further proposing to conclude that the removal of the I/M program will not interfere with other states' ability to attain and maintain the 2008 ozone NAAQS under the good neighbor provision of the Clean Air Act (CAA or Act) and providing additional information related to that conclusion. EPA is now taking comment on the use of this comparison and additional information in this supplemental proposal.