MEMORANDUM UNITED STATES ENVIRONMENTAL PROTECTION AGENCY RESEARCH TRIANGLE PARK, NC 27711

OFFICE OF AIR QUALITY PLANNING AND STANDARDS SUBJECT: Withdrawal ofImplementation Guidance fo**·~"'7"W.l** 6 24-Hour Fine Particle (PM2
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TO: Stephen D. Page, Direc r Office ofAir Quality P Regional Air Directors, Regions I-X
The purpose ofthis memorandum is to announce the U.S. Environmental Protection Agency's withdrawal ofits guidance document titled "Implementation Guidance for the 2006 24-Hour Fine Particle (PM2 .5) National Ambient Air Quality Standards (NAAQS)," dated March 2, 2012. When the guidance document was issued in March 2012, the EPA intended to provide recommendations concerning the development ofstate implementation plans (SIPs) to demonstrate attainment with the 2006 24-hour PM2 .5 NAAQS. To this end, the guidance document addressed multiple topics, including: (i) the overall statutory framework for attainment plans; (ii) basic emissions inventory requirements; (iii) use ofseasonal versus annual inventories; (iv) development ofon-road mobile source emission inventories; and (v) points ofcomparison between the guidance recommendations for the 2006 PM2 .5 NAAQS and the regulatory requirements for the 1997 PM2.s NAAQS. A core premise ofthe guidance document was the EPA's intention to implement the 2006 PM2 . 5 NAAQS pursuant solely to the statutory requirements ofsubpart 1 ofPart D ofTitle I ofthe Clean Air Act (CAA), comparable to the EPA's ·h· regulatory approach to implementation ofthe 1997 PM2
.sNAAQS. On January 4, 2013, however, the U.S. Court ofAppeals for the District ofColumbia (D.C.) Circuit held that the EPA incorrectly interpreted the CAA with respect to statutory requirements for the implementation ofthe 1997 PM2 .5 NAAQS. In Natural Resources Defense Council v. EPA, the D.C. Circuit remanded to the EPA both the final "Clean Air Fine Particle Implementation Rule" (72 FR 20586, April25, 2007) and the "Implementation ofthe New Source Review (NSR) Program for Particulate Matter Less than 2.5 Micrometers (PM2 .5)" final rule (73 FR 28321, May 16, 2008). 1 The Court found that the EPA erred in both rules in implementing the 1997 PM2 . 5 NAAQS pursuant only to the general implementation provisions ofsubpart 1, rather than also the implementationprovisions specific to particulate matter in subpart 4. The Court reasoned that the plain meaning ofthe CAA requires implementation ofthe 1997 PM2
.sNAAQS under subpart 4 because PM2.s particles fall within the statutory definition ofPM 10 and are thus subject to the same statutory requirements. As a result, the Court remanded both rules and instructed the EPA "to repromulgate these rules pursuant to Subpart 4

1 706 F.3d 428 (D.C. Cir. 2013).
Internet Address (URL) • http://www.epa.gov Recycled/Recyclable • Prinled wHh Vegetable Oil Based Inks on Recycled Paper (Minimum 25% Poslconsumer)consistent with this opinion." The same logic would necessarily apply to the implementation ofthe 2006 PM2 

### .s NAAQS pursuant to subpart 4 as well. Given the Court's opinion inNatural Resources Defense Council v. EPA, the EPA is withdrawing its guidance document for the 2006 PM2 

### .s NAAQS. As a guidance document, the EPA was only making recommendations concerning howto meet what it believed were the applicable statutory requirements for PM2.s attainment plans. However, in light ofthe Court's opinion, a core premise ofthe EPA's guidance document (that implementation could proceed pursuant solelyto the requirements ofsubpart 1 rather than also pursuant to the requirements ofsubpart 4) is no longer tenable. Althoughthe Agency is withdrawing the guidance, we will continue to implement the 2006 PM2.s NAAQS under the CAA. The EPA is in the process ofevaluating the effect ofthe January 2013 Court decision onPM2.s NAAQS implementation. As always, states should rely onthe CAA when completing their attainment SIPs for the 2006 PM2 . 5NAAQS. Additionally, the EPA's 1992 General Preamble and 1994 Addendum to the General Preamble provide guidance that may be useful to states.2I encourage your staffto contact OAQPS staffwith specific questions that may arise. Please share this memorandum announcing the EPA's withdrawal ofthe "Implementation Guidance for the 2006 24-Hour Fine Particle (PM2.s) National Ambient Air Quality Standards (NAAQS)" withthe state agencies in your region. Questions should be directed to Rich Damberg at (919) 541-5592 or damberg.rich@epa.gov; and Megan Brachtl at (919) 541-2648 or brachtl.megan@epa.gov.
cc: Sarah Dunham, OAP Greg Green, OAQPS Christopher Grundler, OTAQ Sara Schneeberg, OGC Karl Simon, OTAQ Peter Tsirigotis, OAQPS Richard Wayland, OAQPS Lydia Wegman, OAQPS Geoffrey Wilcox, OGC Anna Wood, OAQPS

2 See, 57 FR 13498 (April 16, 1992) for the General Preamble and 59 FR41998 (August 16, 1994) for the Addendum to the General Preamble.