MEMORANDUM 

UNITED STATES ENVIRONMENTAL PROTECTION AGENCY 

RESEARCH TRIANGLE PARK, NC 27711 

OFFICE OF 

AIR QUALITY PLANNING 

AND STANDARDS 

SUBJECT: Withdrawal of Implementation Guidance fo ·~"'7"W.l 6 24-Hour Fine Particle (PM2.s) 

------------------Nahona~~ ndmd~~~+~r+---------------------------------

FROM: 

TO: 

Stephen D. Page, Direc r 

Office of Air Quality P 

Regional Air Directors, Regions I-X 

The purpose of this memorandum is to announce the U.S. Environmental Protection Agency's 

withdrawal of its 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 of state 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 of seasonal versus annual inventories; (iv) development of on-road mobile source emission 

inventories; and (v) points of comparison between the guidance recommendations for the 2006 PM2.5 

NAAQS and the regulatory requirements for the 1997 PM2.s NAAQS. A core premise of the guidance 

document was the EPA's intention to implement the 2006 PM2.5 NAAQS pursuant solely to the statutory 

requirements of subpart 1 of Part D of Title I of the Clean Air Act (CAA), comparable to the EPA's ·h· 

regulatory approach to implementation ofthe 1997 PM2.s NAAQS. 

On January 4, 2013, however, the U.S. Court of Appeals for the District of Columbia (D.C.) Circuit 

held that the EPA incorrectly interpreted the CAA with respect to statutory requirements for the 

implementation of the 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 of subpart 1, rather than also the implementation provisions 

specific to particulate matter in subpart 4. The Court reasoned that the plain meaning of the CAA 

requires implementation of the 1997 PM2.s NAAQS under subpart 4 because PM2.s particles fall within 

the statutory definition ofPM10 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 of the 2006 

PM2.s NAAQS pursuant to subpart 4 as well. 

Given the Court's opinion in Natural 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 how to 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 solely to the requirements of subpart 1 

rather than also pursuant to the requirements of subpart 4) is no longer tenable. Although the Agency is 

withdrawing the guidance, we will continue to implement the 2006 PM2.s NAAQS under the CAA. 

The EPA is in the process of evaluating the effect of the January 2013 Court decision on PM2.s NAAQS 

implementation. As always, states should rely on the CAA when completing their attainment SIPs for 

the 2006 PM2.

5 NAAQS. Additionally, the EPA's 1992 General Preamble and 1994 Addendum to the 

General Preamble provide guidance that may be useful to states.2 I encourage your staff to contact 

OAQPS staff with specific questions that may arise. 

Please share this memorandum announcing the EPA's withdrawal of the "Implementation Guidance for 

the 2006 24-Hour Fine Particle (PM2.s) National Ambient Air Quality Standards (NAAQS)" with the 

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 FR 41998 (August 16, 1994) for the Addendum to the 

General Preamble.