40 C.F.R. § 51.1003
(a) Nonattainment areas initially classified as Moderate.
(1) For any area designated as nonattainment and initially classified as Moderate for a PM2.5 NAAQS, the state(s) shall submit a Moderate area attainment plan that meets all of the following requirements:
(b) Nonattainment areas reclassified to Serious.
(1) For any nonattainment area reclassified to Serious for a PM2.5 NAAQS under § 51.1002(b), in addition to meeting the Moderate area attainment plan submission requirements set forth at § 51.1003(a), the state(s) shall submit a Serious area attainment plan that meets all of the following requirements:
(2) The state(s) shall submit its Serious area attainment plan to the EPA according to the following schedule:
(i) Discretionary reclassification.
(A) For any nonattainment area reclassified to Serious for a particular PM2.5 NAAQS under § 51.1002(b)(1) because the EPA determined it cannot practicably attain the NAAQS by the applicable Moderate area attainment date, the state(s) shall submit to the EPA no later than 18 months from the effective date of reclassification the portion of the Serious area attainment plan that meets the following requirements:
(1) Base year emissions inventory requirements set forth at § 51.1008(b)(1);
(2) Serious area attainment plan control strategy requirements set forth at § 51.1010(a)(1) through (4); and,
(3) Nonattainment new source review plan requirements pursuant to § 51.165.
(c) Serious nonattainment areas subject to CAA section 189(d) for failing to attain the PM2.5 NAAQS by the applicable Serious area attainment date.
(1) For any Serious nonattainment area that fails to attain the PM2.5 NAAQS by the applicable Serious area attainment date, the state(s) shall submit a revised Serious area attainment plan that demonstrates that each year the area will achieve at least a 5 percent reduction in emissions of direct PM2.5 or a 5 percent reduction in emissions of a PM2.5 plan precursor based on the most recent emissions inventory for the area. The revised attainment plan shall meet the following requirements: