40 CFR § 51.1002 - Classifications and reclassifications.

---
identifier: "/us/cfr/t40/s51.1002"
source: "ecfr"
legal_status: "authoritative_unofficial"
title: "40 CFR § 51.1002 - Classifications and reclassifications."
title_number: 40
title_name: "Protection of Environment"
section_number: "51.1002"
section_name: "Classifications and reclassifications."
chapter_name: "ENVIRONMENTAL PROTECTION AGENCY"
subchapter_number: "C"
subchapter_name: "AIR PROGRAMS"
part_number: "51"
part_name: "REQUIREMENTS FOR PREPARATION, ADOPTION, AND SUBMITTAL OF IMPLEMENTATION PLANS"
positive_law: false
currency: "2026-04-05"
last_updated: "2026-04-05"
format_version: "1.1.0"
generator: "[email protected]"
authority: "23 U.S.C. 101; 42 U.S.C. 7401-7671q."
regulatory_source: "36 FR 22398, Nov. 25, 1971, unless otherwise noted."
cfr_part: "51"
---


# 51.1002 Classifications and reclassifications.

(a) *Initial classification as Moderate PM*<sub>2.5</sub> *nonattainment area.* Any area designated nonattainment for a PM<sub>2.5</sub> NAAQS shall be classified at the time of such designation, by operation of law, as a Moderate PM<sub>2.5</sub> nonattainment area.

(b) *Reclassification as Serious PM*<sub>2.5</sub> *nonattainment area.* A Moderate nonattainment area shall be reclassified to Serious under the following circumstances:

(1) The EPA shall reclassify as Serious through notice-and-comment rulemaking any Moderate PM<sub>2.5</sub> nonattainment area that the EPA determines cannot practicably attain a particular PM<sub>2.5</sub> NAAQS by the applicable Moderate area attainment date.

(2) A Moderate PM<sub>2.5</sub> nonattainment area shall be reclassified by operation of law as a Serious nonattainment area if the EPA finds through notice-and-comment rulemaking that the area failed to attain a particular PM<sub>2.5</sub> NAAQS by the applicable Moderate area attainment date.