UNITED STATES ENVIRONMENTAL PROTECTION AGENCY RESEARCH TRIANGLE PARK, NC 27711

I

I I 

### MEMORANDUM

-

- II 

# MAR 2- 201&

FROM: OFFICE OF 

### SUBJECT: Implementation Guidancefor the 2006 24-Hour Fine Particle (PM2.5) AIR QUALITY PLANNING 

### National Ambient Air AND STANDARDS



### Stephen 

### D. Page, Office of Air Quality



### TO: Regional Air Directors, Regions 

### I-X

II AI Introduction

II II III IIr. 

### Thepurpose ofthis memorandum is to provide guidanceregarding the development of state implementation plans (SIPs)to demonstrate attainment with the 2006 24-hour PM2.5NMQS.' 

### In 2006, the 24-hourPM2.5 standard was strengthenedfrom a level of 65 microgramsper cubicmeter (ug/m3)to a 

### level of 35 ug/m3. The level ofthe annual standard remained unchanged at 15 ug/m3.The designation of 3 1nonattainment areas for the 24-hour standard became effective on December 14,2009, and SIPs for these areas are due no later than three years from the effective date of designation, by December 14, 2012.~ I I I



### The significant health and welfare benefits associated Ah reducing ~~2.5 

### goncentrkions across the country havebeen widely recognized since the initial fine particle NAAQS were established in 1997. Thebenefits of attaining the 1997PM2.5NAAQS and improving health and visibilitywere estimated to be $20-160billion annually, as comparedto an annual cost of $7billion. The benefits of attaining the 2006 24-hour PM2.5NAAQS, when considered incrementallyto the 1997NAAQS, were estimated to be $9-76billion annually, as compared with an annual cost of $5.4 billion.' I 11



### In April 2007, the U.S. EnvironmentalProtection Agency issued a detailed implementation rule to assist
states with the development of SIPs to demonstrate attainment with the annual and 24-$our 1997PM25 NAAQS (the "2007 PM2.5 Implementation ~ule").~ We believe that the overall framewdrk and policy approach of the 2007 PM2.5 Implementation Rule continues to provide effective and appropriate guidance on the EPAYs interpretationof the general statutory requirementsthat states should address in their SIPs. In general, the EPA believes that the interpretations of the statute in the framework ofthe 2007 PM2.5 Implementation Rule are relevant to the statutory requirements for the 2006 24-hour PM2.5 NAAQS, for which SIPs are due by December 14,2012.However, in light of new informationthat has 

## ' See 71 FR 61 144 (October 17,2006).Compliance with the 2006 24-hour PM2,5 NAAQS is determined for a monitoring site by rank-orderingall 24-hour monitoring samples taken over the course of a year, and selectingthe 9gth percentile value (e.g., the 3rd lughest value if there are up to 120 samples during the year). The design value for the site is then calculatedby averaging the 9gth percentile value for each of three consecutive years. Also note that a PM2,3 secondary standardwas set at the same level as the new primary standard.

An additional nonattainment area (a portion of Pinal County, Arizona) was designated on February 3,2011,with an effective date ofMarch 7,2011 (76 FR 6056). The attainment demonstration SIP for this area will be due on March 7, 2014.

The Regulatory Impact Analysis for the 2006 24-hour PM2 NAAQS is available at: http://www.epa.~ov/ttn/ecas/ria.html. See 72 FR 20586 (April25,2007). Internet Address (URL) http://www.epa.gov RecycledlRecyclable Prlntedwith Vegetable 011 Based Inks on Recycled Paper (Mlnlmum25% Postconsumer)become available since the issuance of the 2007 PM2.5Implementation Rule, this memorandum provides additional guidanceto assist states with development oftheir SIPs for the 2006 24-hour PM2.5NAAQS.

Fine particle concentrations in many cities are affected by a combination of regional emissions (from sources like power plants) and local emissions (from sources like local industry, motor vehicles, and residential wood combustion).The regulatory impact analysis conducted for the 2006 24-hourPM2.5 NAAQS placed additional emphasis on the air qualityimprovementsthat could be achieved from local reductions.Wehave observed that some western nonattainment areashave elevated levels of organic carbon on high fineparticle days in the winter time.5Potential contributing sources of these emissions include the combustion of wood and other types ofbiomass in stoves and the use ofhydronic heaters for

, residential 

### and institutional heating. For these areas, SIPs for the 2006 24-hour PM2.5NAAQS may need
to include a heavier reliance on local emission reductionmeasures than SIPs for the 1997PM2.5 NAAQS. Therefore,this memorandum includes guidance for states that have nonattainment areas with exceedances occurring exclusively during one season ofthe year.

The first section ofthis memorandum reviews the overall framework and basic statutoryrequirements for SIPsto demonstrate attainment with the 2006 24-hour PM2.5NAAQS, consistent with the 2007 PM2,5 ImplementationRule. This section also suggests additional considerations for states in the development of their SIPs. The next sectionsprovide guidance to states regarding the use of emissions inventories (including seasonalinventories, for some areas) for SIP planning (e.g.,reasonable further progress (RFP) plans and attainment demonstrations). The last section describes how specificinterpretations of the statute as outlined in various provisions in the regulatory text ofthe 2007 PM2.5 Implementation Rule could help inform attainment plans for the 2006 24-hour PM2.5NAAQS.

Please share this guidance with the state agencies in your Region. It is importantto note that any guidance containedherein is not binding on the states, the public, or the EPA.

Overall Framework for State Implementation Plans to Demonstrate Attainment

SIPs for areas violating the 2006 24-hour PM2.5NAAQS shouldmeet the basic Clean Air Act (CAA) requirements set forth in section 172. The EPA outlined its interpretation of many of these provisions in the 2007 PM2.5Implementation Rule. In addition to regulatory provisions, the EPA provided substantial general guidance for attainmentplans for PM2.5in the preamble to the final the 2007 PM2.5 ImplementationRule. This section of this document includes details regarding these interpretations, and provides additiongl guidance, where applicable for purposes ofthe 2006 24-hour PM2.5NAAQS.

Under the CAA, each attainmentplan needs to demonstrate that the area will attain the NAAQS "as expeditiously as practicable," but no later than five years from the effective date of the designation of the area. See section 172(a)(2)(A).If attainment within five years is considered impracticable by a state due to the severity of an area's air qualityproblem and the lack of available control measures, the state may propose in its attainment plan an attainment date ofmore than five years but not more than ten years fiom designation. The EPA will evaluate the appropriateness of the state's proposed attainment date during its rulemaking action on the attainment plan submission.

Frank, N. The Chemical Composition of PM2.3 to SupportPM2.5 Implementation. hm://www.ewa.gov/ttnlnaa~sl~m/presentslcmnt prn monitoring data for weciation-neil frankmt, presented at "The PM2.5 Implementation Program and the Area Designation Process for the 2006 PM2.3 StandardsTraining Workshop Presentations," Chicago IL, June 20-21, 2007.To determine the most expeditious attainment date for an area, we recommend that states first identify emission reduction programs that have already been adopted and arebeing implemented at the federal, state, and local levels. States could then use this information to evaluate, through air quality modeling or other technical analyses, the amount of air quality improvement such programs are projected to provide for the nonattainment area within five years ofthe date of designation. For example, the EPA finalized the Transport Rule (also known as the Cross State Air Pollution Rule) in July 201 1, which is expected to achieve significant reductions in sulfur dioxide (SO2)and nitrogen oxides (NO,) emissions from central and eastern statesby 2014.~ In addition, the EPA has promulgated a number of regulations over the past decade to reduce emissions from many types of mobile sources (e.g., Tier 2 on-road vehicle and standards; the 2007 heavy duty highway vehicle, engine and on-road diesel fuel rule; various non-road engine, vehicle and equipment regulations; the locomotive and marine engine rule; and the ocean-going vessel rule). All of these regulations will provide emission reductions over a broad region, which are expected to help many nonattainment areas attain the 2006 24-hour PM2.5NAAQS.~

Next, we recommend that states evaluate additional control measures and control technologiesreasonably available control measures (RACM) and reasonably available control technology (RACT)- for an area. Under the CAA, states are required to impose RACM and RACT that canbe implemented

on sources located in nonattainment areas and to adopt enforceable regulations to ensure these areas will attain as expeditiously as practicable. See section 172(c)(l).The 2007 PM2.5 Implementation Rule requires that states evaluate potential RACWRACT control measures for sources of direct PM2.5, SO2, and NO,.' We recommend that states follow a similar approach for identifying which pollutants to control in a given nonattainment area for the 2006 24-hour PM2.5NAAQS. When acting upon a state's attainment plan, the EPA will evaluate the state's approach for determining which pollutants to control.

The 2007 PM2.5 Implementation Rule also requires that after January 1,2011, for purposes of establishing emissions limits for RACT and RACM, states establish such limits taking into consideration the condensable fraction of direct PM2.5 

## emission^.^ The reason for this delay in connection with the 1997PM2.5NAAQS was the need for EPA to reevaluate the test methods for measuring condensable emissions. On December 21,2010 (75 FR 80118),the EPA published a final notice with the revised Methods 201A and 202 providing for a more accurate emissions test. Thus, the EPA believes that to meet the statutory requirements of section 172, states should address condensable emissions in the context of evaluatingRACMIRACT for affected sources for the 2006 24-hour PM2-5NAAQS.

The final Transport Rule was published in the Federal Register on August 8,2011 (76 FR 48208). Throughthis rule, emission reductions are expected to be achieved beginning in 2012 (76 FR 48214). On December 30,2012, the District of Columbia Circuit Court (the Court) issued an order addressing the status of the Transport Rule and the CAIR in response to motions filedby numerous parties seelung a stay of the Transport Rule pending judicial review. In that order, the Court stayed the Transport Rule pending resolution in 2012 of the petitions for review of that rule in EME Homer Generation, L.P. v. EPA (No. 11-1302 and consolidated cases).

Note that section 110(a)(2)(D)(i)(I)of the CAA requires a state to ensure that emissions from sources or activities within the
state do not contribute significantly to nonattainment in, or interfere with maintenance by, any other state.

The 2007 PM2,, Implementation Rule includes a presumption that sources ofNO, must be evaluated for control measures, unless the state and the EPA demonstrates that NO, emissions from the state do not significantly contributeto P& concentrations in the nonattainmentarea. It also includes a presumptionthat the state does not need to evaluate sources of volatile organic carbon (VOC) or ammonia for control measures, unless the state or the EPA demonstrates that VOC or ammonia emissions from the state do significantly contribute to PM2,,concentrationsin the nonattainment area. The EPA believes that these same presumptions would be appropriately applied with respect to the 2006 24-hour PM2,, NAAQS as well.

see section 5 1.1002(c)of the 2007 PM2.3ImplementationRule.Section 172 requires states to adopt measures that are RACMIRACT for the specific nonattainment area. In accordance with section 172, the preamble ofthe 2007 PM2.5 Implementation Rule provides extensive guidance for considering technical and economic feasibility for potential control measures.1°We recommend that states follow a similar approach to evaluate RACWRACT for the 2006 24-hour PM2.5 NAAQS. Potential measures that are reasonably available considering technological and economic feasibility would need to be adopted as RACMIRACT if, considered collectively, they would advance the attainment date by one year or more. The EPA has long taken the interpretation that section 172 of the CAA does not require adoption of measures that could not collectively advance attainmentby at least a year.

We recommend that a state's plan indicates whether the area can attain within five years of designation on the basis of emission reductions from existing programs and any new RACMIRACT measures that could be adopted. The EPA believes that while areas projected to attain within five years of designation as a result ofmodeling of existing national measures should still be required to conduct a RACT and RACM analysis, such areas maybe able to conduct a limited RACT and RACM analysis that does not involve additional air quality modeling. A limited analysis of this type could involve the review of available reasonable measures, the estimation of potential emissions reductions, and the evaluation of the time needed to implement these measures.l2
If the state determines, based on the severity of its nonattainment problem and the feasibility ofpollution control measures, that it cannot attain the NAAQS within five years, then it would need to conduct further analyses to determine what attainment date (e.g., between six and ten years) would represent attainment "as expeditiously as practicable." In order to support a requested attainment date of more than five years after the effective date of designation, the state should ensure that it has done a thorough evaluation ofpotential RACWRACT measures. The state analysis should demonstrate that sufficient control measures could not be adopted and implemented cumulativelyin order to establish an attainment date at least one year earlier.

The 2007 PM2.5 Implementation Rule identifies a number of key source categories that can contributeto fine particle concentrations across the country. It recognizes that each nonattainment area has its own unique characteristics and mix of sources contributing to the problem. For this reason, the 2007 PM2.5 Implementation Rule neither requires specific control measures to be implemented in every nonattainment area, nor includes a specific source size threshold for the RACMIRACT analysis. The rule recognizes, however, that a state needing significant emissions reductions to attain the NAAQS in a given area will likely need to evaluate controls for smaller sources, while a state with an area that exceeds the NAAQS by only one microgram per cubic meter may not. We believe that a similar approach would be appropriate for the 2006 24-hour PM2.5NAAQS. Accordingly, we recommend that states with more severe nonattainment problems evaluate controls for smaller sources.

10 In June 2007, Earthjustice filed apetition for reconsideration of the 2007 PM2,5 Implementation Rule, which asserts that the final rule revised well-established criteria used to determine the economic feasibility of controls being considered for RACT (i.e., that a source in a particular source category should be able to afford emission controls similar to controls applied by other sources in that same category) without any explanation of the legal or policy arguments in support of the new interpretation of the statute. On April 25,2011, EPA granted the petition for reconsideration on this issue and intends to address the petition soon.
11 See 57 FR 13498, 13560 (April 15, 1992) and 44 FR 20372,20374 (April 4,1979). In addition, the EPA has consistently interpreted RACM as a collection ofmeasures that would advance the attainment date by at least 1 year, and the courts have determined that the statutory RACM requirement is ambiguous and deferred to EPA's interpretation of the requirement. See Sierra Club v. EPA, 314 F.3d 735,744 (5th Cir. 2002) and Sierra Club v. EPA, 294 F.3d, 155 162 (D.C. Cir. 2002).

"See 72 FR 20612-20613 of the 2007 PM2,5 Implementation Rule.Air quality modeling is commonlyused to demonstrate the level of air qualityimprovement that is projected from implementation of existing emission reduction programs and additional RACMIRACT measures under consideration. The details of emission inventory processing for attainment demonstrations and air quality modeling approaches are addressed in the EPA's modeling jpidance. l3

Thepreamble to the 2007 PM2.5 ImplementationRule includes the consideration of RACMIRACT for sources participatingin a regional trading program. Specifically,the preamble established apresumption that compliancewith the Clean Air Interstate Rule (the CAIR) would satisfyRACMIRACT requirements for SO2and NO, emissions from electric generatingunits (EGUs) in states participating in the CAIR cap-and-trade program for such emissions.14The rule indicated that states could presume that EGUs located within a given nonattainment area were meeting the RACMIRACT requirement, based solely upon a regional program that imposed controls on sourcesboth within and outside designated nonattainment areas.

In June 2007, Earthjustice filed a petition that raised objections to this guidance and asserted that under the CAA, compliance with a regional tradingprogram, such as the CAIR, should not be presumed to satisfy RACMIRACTrequirementsfor individual EGU sources located in nonattainment areas. On a related issue regarding whether compliance with the NO, SIP Call constituted RACT for sources in nonattainment areas, in 2009 the United States Court ofAppeals for the District of Columbia Circuit held that allowing use of the NO, SIP call to constituteRACT without any locally applicable analysis regarding the equivalence ofNO, SIP Call and RACT reductions: "is inconsistentwith the Clean Air Act



### . . .in allowingparticipation in a regional cap-and-trade program to satisfy an area-specific statutory mandate."15 

### In light of this decision, on April 25,2011, the EPA granted the Earthjustice petition for reconsideration ofthe PM2.5presumptionthat CAIR satisfied RACMIRACT requirements for individual EGU sources located in nonattainment areas. For purposes of establishingRACT for EGU sources for the 2006 24-hour PM2.5NAAQS, states wishing to rely on regional trading programs should demonstrate that any such program produces RACT-level reductions within the nonattainment area.

As mentioned earlier, it is likely that SIPSfor the 2006 24-hour PM2.5 NAAQS may need to include a greater emphasis on reducing emissions from local sources as compared to plans to attain the 1997PM2.5 NAAQS. The EPA recommends that states consider studies in the published literature, which have indicated that emissionreductions of direct PM2.5produce higher estimated healthbenefits per ton than reductions of other pollutants, such as SO2or

## NO,.^^ In addition, there are studies available that provide methods for maximizing health benefits and minimizing risk inequalityin designinglocal scale air quality plans.l7

l3 See the EPA Office of Air Quality Planning and Standards, April 2007. Guidance on the Use ofModels and Other Analyses for Demonstrating Attainment of Air Quality Goals for Ozone, PM2,5, and Regional Haze. (EPA-454lB-07-002). See also "Update to the 24 Hour PM2,NAAQS Modeled Attainment Test" available at http:l/www.~a.aov/tbv'scraml~idance/~ide~~date to the 24-hour PM2.5 -Modeled AttainmentTest.udf.

l4 See Implementation Rule, 72 FR 20623-5.

l5 SeeNRDC v. EPA, 571 F.3d 1245 (D.C. Cir. 2009).

l6 Fann, N., Fulcher, C., and B. Hubbell, 2009. The Influence of location, source, and emission type in estimates of the human health benefits of reducing a ton of air pollution. Air Quality, Atmosphere & Health. Volume 2, Number 3, 169-176, June 2009.

l7 Fann et. al., 2011.Maximizing health benefits and minimizing inequality: incorporating local-scale data in the design and evaluation of air quality policies. Society for Risk Analysis, vol. 3 1,no. 6, p. 908-922, June 201 1.After conducting a RACMIRACT analysis, the state needs to include a plan showing that the area will make ongoing RFP toward attainment as required by section 172(c)(2),which is commonly expressed in
terms ofincremental emission reductions and air quality improvementby certain interim milestone years.l8 (RFP issues are discussed in greater detail later in this guidance).

All SIPSalso should include contingency measures that would take effect without hrther actionby the
state or the EPA in the event that the area fails to meet an RFP milestone or to attain by its attainment date. See CAA section 172(c)(9).Contingency measures should provide for emission reductions that would result in a level of air quality improvement comparable to one year of improvement to be achievedby the submitted SIP. (Contingency measures are discussedin greater detail later in this guidance).

Other programs required under the CAA to be implemented in any nonattainment area include new source review, transportation conformity, and general conformity. These programs are not discussed in detail in this memorandum. Each program is governedby a series of separate regulations and guidance documents. Information on new source review can be found at: http://www.epa.gov/nsr. In addition, information on transportation conformity, including the links to the current regulations and relevant guidance documents, can be found at: 

### http://www.epa.~ov/otaq/stateresources/transconf/index.htm. For information on general conformity, please visit: 

### htt~://www.e~a.~ov/air/~enconform/back~ound.html.

Emission Inventory Components for 

### SIP Development

Emission inventory data serve as the foundation for various types of analyses that enable states to estimate the degree to which different source sectors contribute to the nonattainment problem, as well as to estimate the air quality improvement that can be achieved through different control measures. The EPA recommends that states use the best available, current emissions inventory information for SIP development. High quality emission inventory data are essential for the development of an effective attainment demonstration. Emission inventories shouldbe consistent with the nature of the air quality problem and the types of emission reduction strategies that will be implemented and relied upon as part of the plan.

Emission inventory data element requirements are codified in 40 CFR Part 5 1, Subpart A. Under this regulation, states are required to provide annual statewide inventory data for selected categories, regardless of an area's attainment status. Through 40 CFR Part 5 1, Subpart A, states are required to report primary (i.e., "direct") PM2,5, which is defined as the sum of filterable PM2.~ and condensable PM.'~ This regulation also requires reporting of SO2,NO,, volatile organic compounds (VOCs), and ammonia-potential precursors to PM2.5. States submit these emissions data to EPA electronically, and the EPA merges these data with emissions data from other sourcesto form the national emissions inventory (NEI) every three years.

l8The 2007 PM2,5 Implementation Rule states that an approvable implementation plan (submitted three years after designation) which shows the area will attain within five years after designation will be deemed to meet the RFP requirement. The EPA believes a similar interpretationwould be appropriate for the 2006 24-hourPM2.5NAAQS.

l9under 40 CFR Part 5 1, SubpartA, filterable PM2,5 is defined as particles that are directly emitted by a source as a solid or liquid at stack or release conditions and captured onthe filter of a stack test train. Filterable PM23 is particulate matter with an aerodynamic diameter equal to or less than 2.5 micrometers. CondensablePM is defined as material that is vapor phase at stack conditions, but which condenses and/or reacts upon cooling and dilution in the ambient air to form solid or liquid PM immediately after discharge from the stack. Note that all condensable PM, if measureable and present from a source, is typically in the PM2,5 size fraction, and therefore all of it is a component ofboth primary PM2.5 and primary PMlo.CAA section 172(c)(3)includes the emissions inventoryrequirements for nonattainment areas. Under this section of the CAA, inventories for the nonattainment area must include a comprehensive, accurate,
current accounting of actual emissions from all sources in the nonattainment area. The EPA believes that by requiring an accounting of actual emissions from all sources,the language in section 172(c)(3)is intended to include all emissions that contributeto the formation of a particularNAAQS pollutant. Therefore, for the 2006 24-hour PM2.5NAAQS, this would include direct PM2.5 (both filterable PM2.5 and condensablePM), as well as potential precursors (SO2,NO,, VOCs, and ammonia).

We expect that for many nonattainment areas, the annual statewide inventories that are developed under 40 CFR Part 5 1, SubpartA will serve as an appropriate starting point for the emissions inventories used for SIP development.For example, a state may choose to refine the annual statewide inventory to focus

on particular sources within a nonattainment area. Although annual statewideinventories are required under 40 CFR Part 51, SubpartA, we believe that it may be appropriate in certain circumstances for
states to use seasonal inventories for SIP development. More information regarding the use of seasonal inventories is included in the section "The Use of Seasonal Versus Annual Inventories."

There are several different types of inventories that are developed for SIP planning. Statesusually submit these inventories to the EPA in conjunctionwith the SIP revision they support, such as an attainment demonstration, an RFP plan, or a maintenanceplan. If deemed appropriate, the EPA approves the inventory into the state's SIP. In light of this formal approvalprocess, the EPA requires these inventories to contain thorough documentationofhow the emission estimates were prepared.

A brief description ofthe different types of emissioninventories used for SIP development is provided below. These inventories are not developed at the same time, but rather, are developed over a number of years as SIP revisionsbecome due.


# + Base YearInventory for theNonattainment Area. This inventory is commonly used as a starting point for both the attainment demonstration and the RFP plan for an area. As required under section l72(c)(3), this inventory should include a comprehensive, accurate, current accounting of actual emissions from all sources in the nonattainment area (i.e.,point, nonpoint area, on-road, and nonroad sources). The base year inventory should represent emissions for one of the three years on which the area was designated nonattainment.We recommend that to meet the statutory requirements of section 172(c)(3),the base year inventory for the nonattainment area includes emissions of direct PM2.5 (both filterablePM2.5 and condensable PM), as well as potential precursors (SO2,NO,, VOCs, and ammonia).



### + ProjectedAttainment Year Inventory for the Nonattainment Area. Theprojected attainment year inventory includes estimated emissions for all types of emission sources located in the nonattainment

area for the year in which the area is expected to attain the NAAQS, consistentwith the attainment demonstration due three years after nonattainment designation. This inventory includesprojected emissions for the attainment year, taking into consideration assumptions about emission changes expected since the base year, as well as any expected emission reductions from existing control
measures, and any new measures that may be adopted as part ofthe local area attainment plan. The projected attainmentyear inventory for the nonattainment area can be used to calculate emissions milestones for RFP plans and motor vehicle emissions budgets, as needed for a particular area. As such, we recommend that the projected attainmentinventory for the nonattainment area includes direct PM2.5, SO2, presumptively NO,, as well as other precursors that have been determined to be significant through the area's SIP developmentprocess.

### + RFP Inventories. Per section 172(c)(2),states must include a plan showing that the area will make ongoing RFP toward attainment, which is commonly expressed in terms of incremental emission reductions and air quality improvementby certain interim milestone years. The EPA recommends that the RFP inventories include direct PM2.5,SO2, and presumptivelyNO,, as well as other precursors that have been determinedto be significant through the area's SIP developmentprocess.20 The 2007 PM2.5 Implementation Rule provides guidance on determining target emission reduction levels to be achieved by interim milestone years for those pollutants included in the attainment demonstration. It also discusses an alternative approach inwhich a different mix of pollutant changes would be acceptable if it is expected to provide an approximately equivalent level of air quality improvement.



### + Motor Vehicle Emissions Budgets. Motor vehicle emissions budgets ("budgets") are used for transportation conformity determinations and typically reflect emissions from on-road mobile sources included inthe attainmentyear and any RFP inventories for the nonattainment area. They are used in analyses to determine whether a transportation plan or transportation improvement program is consistent with the SIP and therefore would not cause or contribute to a violation of the NAAQS, delay timely attainment, or interfere with any interim milestones. The EPA recommends that motor vehicle emissions budgets include direct PM2.5 and presumptivelyNOx,as well other precursors that have been determined to be significant through the area's SIP developmentprocess.21 For a further discussion on motor vehicle emissions budgets for PM2.5precursors see 70 FR 24283-5 and 

### 24287.



### 3 Attainment Demonstration Modeling Inventories. These inventories include detailed spatial and temporal elements needed to support air quality modeling, and in some cases, use methods that estimate emissions on a daily or hourly basis. There are two types of attainment demonstration modeling inventories:

1) 

### Base 

### Year [Baseline)AttainmentDemonstration Inventory

### for Modeling. The base year inventory for attainment demonstration modeling commonly represents emissions from an area (sometimes a multi-state area) that may contribute to fine particle concentrations in the nonattainment area. The base year inventory should represent the best available inventory information, but the statehas flexibility in determining the specific year to use.22 The availability of good quality meteorological information and complete air quality data for the

samebase year is also an important consideration in selecting a base year to use. For purposes ofphotochemical modeling, we recommend that states include direct PM2.5(both

20 The pollutant coverage of RFP assessments is determined on an area-specific basis according to each area's attainment demonstration.In addition, for demonstrating RFP, states may choose to applyvarious control levels to various pollutants, so long as overall emission reductions are adequate. See 72 FR 20638-20639 ofthe 2007 PM2.5Implementation Rule for more information. 21~he EPA does not expect that stateswill establish motor vehicle emissionsbudgets for SO2 because on-road emissions of SO2are at de minimis levels.

22 In some cases, the base year (baseline) attainment demonstration inventory selected for use in the attainment demonstration may be a different year from the base year inventory for the nonattainment area mentioned above. This could happen if, for example, meteorological conditionswere abnormal during the selectedbase year inventory for the nonattainment area. Attainment demonstration modeling seeks to use meteorological years or episodes that are generally conduciveto PM2,5 formation. See the EPA's PM2,5 modeling guidance for more information.

### filterablePM2.5 and condensable PM), as well as potential precursors (SO2,NO,, VOCs, and ammonia) in order to ensure that PM2.5 concentrations are accuratelymodeled.23

2) 

### ModeIed 

### (Proiected')

### Attainment 

### Year Inventory

### for demon st rat in^ Attainment. This inventoryrepresents projected future year emissions for the overall modeling domain (sometimes a multi-state area), taking into consideration assumptions about emission changes expected since the base year, as well as any expected emission reductions from existing control measures, and any new measures that may be adopted as part ofthe local area attainmentplan. Air quality modeling analyses evaluate the projected change in future year air quality concentrations in nonattainment areas relativeto air quality concentrations observedin the base year. For purposes ofphotochemical modeling, we recommend that
states include direct PM2.5 (both filterablePM2.5 and condensable PM), as well as potential precursors (SO2,NO,, VOCs, and ammonia) in order to ensure that PM2.5 concentrations are accuratelymodeled.24



### 3 Maintenance Plan ~nventories.~~ 

### When an area has attained the standard, the state may submit a request to redesignate that area from nonattainmentto attainment. The requirementsfor a request for redesignation are outlined in section 107(d)(3)(E)of the CAA.

These requirements include:

- 

### The EPA determines that the area has attained the NAAQS (i.e., the most recent three years of complete quality assured data in AIRS-AQS show attainment);

- 

### The EPA has fully approved the area's applicable implementation plan under section 11 0(k) of the CAA;

- 

### The EPA determinesthe improvementin the area's air qualityis due to enforceable reductions in emissionsresulting from implementation of the applicableimplementation plan, applicable Federal air pollution controlregulations, and other permanent enforceable reductions;

- 

### The area has a fully approved maintenanceplan meeting section 175Aof the CAA; and

- 

### The state has met all ofthe requirements applicable (forpurposes ofredesignation) to the

areaunder section 11 0 (the applicable infrastructureSIP requirements) and Part 

### D (the applicablenonattainment area SIP elements).

The maintenanceplan provides for the maintenance ofthe NAAQS in the area for at least 10 years after the redesignation (i.e., for at least 10years from the EPAYs final rule approving the redesignation). Three sets of emissions inventories are used for a maintenance plan to demonstrate maintenance under section 175A:attainment year, interim year, and final year inventories. The first represents 

### an actual attainment year inventory, while the second and third are projections of future emissions.

-

23 In some cases, where local primary PM2.5emissions are the dominant source of PM23 exceedances,it may be appropriate for an attainment demonstration to rely solely on dispersionmodels or rollback techniques. In these cases, modeling of precursors may not be necessary as long as attainmentofthe NAAQS can be adequately demonstrated.

24 Ibid.

25 This guidance document does not, and is not intended to, provide specific details regarding redesignationrequests and maintenance plans. However, we believe it is helpfulto include information here regarding maintenance plan inventories.1) Maintenance Plan Attainment Year Inventory. As part ofthe maintenance plan, the state submits an attainment year inventory characterizing emissionsin the maintenance area. This inventory is from one of the years in three-year period in which the area monitored attainment.

2) Maintenance Plan Interim Year Inventory. At least one interim year inventory is used to demonstrate that emissionsin the area are not expected to exceed the attainment year inventory in the interim between the base year and the last year of the maintenance plan. The demonstration, by means of an interim year inventory, that the area will maintain the standard throughout the maintenance period is derived from CAA section 175A,which states that maintenance in the area is to be provided "for at least ten years after the redesignation," and not just inthe final year. Thus, a maintenance plan includes at least one interim year inventory to establish that, during the period that maintenance is projected, emissions will remain at or below the level of the attainment year inventory.

3) Maintenance Plan Projected Final Year Inventory. This inventory includes projected emissions for the maintenance area for a period ending 10years after EPA's final approval of the redesignation and maintenance plan. As stated above, section 175A requires a demonstration that the area will continue to attain the standard throughout the 10-year maintenance period. The maintenance plan final year inventory reflects assumptions about expected emissions changes in the maintenance area over the 10-year period due to ongoing and new national, state, and local requirements as well as other future

## condition^.^^ In identifying an appropriate projection year, the state should factor in the time necessary for the EPA to review and take action on the redesignation request and maintenance plan, considering that CAA section 107(d)(3)(D)provides the EPA with up to 18months after a complete redesignation request is submitted. The EPA recommendsto states that the maintenance plan demonstrate maintenance for 12years from the time of formal submittalto allow for completion of the redesignation rulemaking process. The EPA also recommends that when the state is in the initial stages of developing the maintenance plan, the state should consult with its EPA Regional Office on an appropriate year for the final year inventory.

The Use of Seasonal Versus Annual Inventories

As mentioned earlier in this memorandum, statewide annual emission inventories are required under 40 CFR Part 51, SubpartA. We expect that for many nonattainment areas, these annual inventories will

serve as an appropriate starting point for the emissions inventories used for SIP development. In contrast with the 1997 annual PM2.5NAAQS, where states rely only on annual inventories in the implementation process, the 2006 24-hour PM2.5NAAQS is designed to protect against peak exposures. Thus, for the 2006 24-hour PM2.5NAAQS, there are some circumstances in which the EPA believes that seasonal inventoriesmaybe useful for SIP planning purposes. For example, we have observed that in some nonattainment areas, all ofthe highest fine particle concentrations over the course of a year occur in one

season. 27

26 The maintenance plan would also establish motor vehicle emissions budgets for the last year of the maintenance period, and could include budgets for an interim year(s) if the area chooses to do so. Any budgets would address direct P&, NOx, and any other precursors that the maintenance plan identifies as being significant in order for the area to maintain the NAAQS.

27 For more information, see:If exceedances occur during only one season for each of the years on which the nonattainment designationisbased, and this is the case for all subsequentyears, we recommend that states develop a seasonal inventory and that they use this inventory for SIP planning purposes. We believe that, for some areas, a seasonal approach will enable statesto expend fewer resources to determinewhich controls may be most effective for reducing concentrations of concern.For example, emission reduction strategies would not need to be evaluated for all seasons. In addition, fewer modeling runs may be needed to establish mobile source emission inventories (see the next section regarding the use of the Motor Vehicle Emission Simulator (MOVES)model). The determination regardingwhether or not to use a seasonal inventory will be area-specific, however. The EPA recommends that each stateworks in consultation with it EPA Regional Officeto characterize an area and to assess whether seasonal inventories are needed for sources that cause violations in a particular season.

To consider whether a seasonal inventorywould be appropriate for an area, the EPA recommends that states first assess the nature of the fine particle problem in that area, focusing on the seasonalityof the problem. This assessment should include consideration of information about the months during which the area experiences its ex~eedances;~~ the meteorology on the days with exceedances; and insights from fine particle "speciation" (chemical composition) data about key local and regional sources contributing
to the area's exceedances.For example, we have observedthat a number of nonattainment areas have elevated levels of organiccarbon on high fine particle days only in the winter.29 Common sources contributing to high organic carbon concentrationsin this season include the combustion of wood and other types ofbiomass in stoves and the use ofhydronic heaters for residential and institutionalheating. Often these high PM2.5 levels occur during multi-day episodes characterizedby cool temperatures, low wind speeds, and inversion conditions in which cool air traps pollutants close to the ground and limits mixing in the atmosphere. The EPA has developed the "Strategies for Reducing Residential Wood Smoke" resource guide to provide states, local, and tribal governments with information on education and outreach tools, as well as regulatory approaches (e.g., example ordinances) and incentive-based programs to reduce wood smoke. The resource guide also provides information on calculating emission reductions from wood stove and fireplace changeoutlretrofitprograms and wood smoke curtailment programs. For more information, visit: 

### http://www.epa.~ov/~caaalltlImemoranda~strate~es-doc-8-11- 09.pdf.

We have also observed that some areas in the northern states have elevated ammonium nitrate levels in the winter, as nitrate remains in particle form and does not volatilize at lower temperatures.High ammonium nitrate levels are caused by the reaction ofNO, and ammonia gas in the atmosphere.NO, emissions result from many sources that burn fossil hels, such as cars, diesel trucks, non-road engines, and various industrial sources.

To further assess the nature of the fine particle problem in an area, we recommend that statesinvestigate the sourcemix for the season in question versus a longer-time averagingperiod (e.g., an annual average). "Sourcemix" refers to the contribution of sources in question to the total PM2.5 mass for the

28 The word "season" is not intendedto imply specific months out of the year. For example, in some areas, the winter season may span from October through March, where in other areas, it could span from December through February.Note also that if an area experiences a high PM2,3 event that occurs outside of the seasonbeing considered for a seasonal inventory, a seasonal inventory may still be appropriateif the event meets the definitionof an exceptional event under 40 CFR 50.1 and is determined to be an exceptionalevent in accordance with 40 CFR 50.14.

29 rank, N. The Chemical Compositionof PM2.3 to SupportPM2.3 Implementation. hrtp:IJwww.e~a.gov/~n~~~/wmlpre~enrs/~~mnt am monitoring. data for s~ecistion-neil fr-ank.ppt, Presented at "ThePM2,,Implementation Program and the Area Designation Process for the 2006 PM2,5 StandardsTraining Workshop Presentations," Chicago IL, June 20-21,2007.time period in question. The source mix canbe assessed using information such as inventory data and

source attributiodsource tagging studies, in which ambient PM2.5 data or model output is apportionedto various source category types.
When development of a seasonal inventory would be appropriate, the EPA recommends that states give additional attention to refining emissions estimates for key source categories which operate predominantly during the relevant season (e.g., woodstove emissions in winter).30 When following a seasonal approach, the EPA believes that the control strategy evaluation (based on seasonal emission reduction measures) and the assessment of htureyear air quality concentrations (through air quality modeling or other analyses) shouldbe conducted for that season.31 

### In addition,if a seasonal inventory approachis used, then the transportation conformity budget should pertain to the relevant season. States should work with their EPA Regional Offices to develop their seasonal inventories. This collaboration, for example,may help states determine the appropriate temporal resolution that will correlate well with the types of days that exceedances are recorded in the area.

Developing On-Road Mobile Source Emission Inventories

The EPA recommends that when developing their SIPs for the 2006 24-hour PM2.5NAAQS in areas outside of California, states use ofthe most recent version ofthe MOVES model to estimate on-road emissions of direct PM2.5,NOxand other precursors deemed significantby the state for ~1~s.~~ MOVES is a state-of-the-art upgrade to the EPA's modeling tools for estimating emissions from highway vehicles, based on analysis ofmillions of emission test results and considerable advances in the Agency's understanding of vehicle emissions. The MOVES model provides updated vehicle emission factors, with particular improvements in the characterization of vehicle emissions under varying temperature and vehicle speed and power conditions over its predecessor MOBILE. For example, MOVES provides much better estimates of direct PM2.5 emissions from both diesel and gasoline vehicles and accounts for how emissions vary with temperature throughout the year. The contribution of on-road motor vehicles to a nonattainment area's PM2.5 problem depends on numerous factors, including local diesel truck traffic, fleet mix, and vehicle-miles-traveled (VMT) growth.

On-road inventories and motor vehicle emissions budgets for transportation conformity purposes would include direct PM2.5,NOx,and any other precursor emissions deemed significantby the state for their 

## SIP.^^ For each relevant year, areas should choose MOVES inputs for the season ofthe year when

30 If more information is desired onhow various emission sectors are temporally allocated, please see htt~://www.e~a.~ov/ttn~chie~emch/index.html#related. If additional information is required, please contact Tesh Rao at rao.venkatesh@,epa.gov.

31 Modeling should be limited to a single season only in cases where exceedances in other seasons have not occurred in the past and are not expected to occur in the future (based on ambient data and analysis of emissions). See the modeling guidance for more information. 32~he EPA has indicated that it expected all SIPs for areas outside of California for the 2006 24-hour PM,,, NAAQS to include estimates of on-road emissions based on results from the MOVES model. (See question 6 ofthe guidance document titled, "Policy Guidance on the Use of MOVES2010 for State Implementation Plan Development, Transportation Conformity, and Other Purposes." MOVES2010a is the current version of MOVES available for use in SIP preparation outside of California. However, state and local agencies should refer to the MOVES webpage to determine the version of MOVES to be used when they begin work on their SIP for this NAAQS. Thls web page also contains links to guidance documents on the use of MOVES. The MOVES web page is available at: http://www.epa.gov/otaq/models/moves/index.htm. State and local agencies in California would use the most recent version of EMFAC in the preparation of SIPs for this NAAQS

. 33 A small number of areas may determine that either re-entrained road dust or dust from the construction of transportation projects are significant contributors to their PMz,5 problems and include those emissionsin the area's motor vehicle emissions budgets. [40 CFR 93.102(b)(3) and 93 CFR 122(f)(2)].Re-entrained road dust emissions would be calculated using the latestexceedances have occurred.If exceedances occurred in only one season for multiple years, then emissions should be estimated using MOVES inputs and other data that are relevant for that season. The resulting on-road inventories and motor vehicle emissionsbudgets would be for a 24-hourperiod (calculated in MOVES using the hourly time aggregation optionwith averagehourly meteorology and activity) as representative days." For example, if the SIP demonstrates that exceedances occurred only during the winter, the inventory and motor vehicle emissions budgets should be developed for only that

season using MOVES inputs for parameters such as temperature, humidity and fuel properties that are consistent with winter time conditions. 

### In this example, the SIP'Sinventory and motor vehicle emissions budgets would also be based on the best available information concerningwinter time VMT, speeds, and other relevant data.

If exceedances occur in more than one season,then on-road inventories should be calculated for the 111 year using appropriateMOVES inputs and other data to accurately estimate on-road emissions.

Based on the informationprovided above, we thereforerecommend that motor vehicle emissions budgets are established in one oftwo ways:

1. The SIP could establish motor vehicle emissionsbudgets for direct PM2.5,NOx and any other relevant precursors for such areas on an annual basis consistent with the calculation of annual on-road inventories; or

2. The SIP could establish motor vehicle emissionsbudgets for direct PM2.5,NOxand any other relevant precursors for the one season of the year when on-road motor vehicles make the
most significantcontribution to an area's PM2.5 exceedances.

For example, an area may choose to take the second approach in its SIP because it can show that motor vehicles make the most significant contributionto exceedances in the winter. This may be the case if direct PM2.5 emissions fiom gasoline powered vehicles are higher during that time of year and NOx emissions from on-road vehicles contributeto nitrate concentrationsthat are higher in the winter than in the summer. Alternately, if an area had exceedances during the summer, the SIP may show that the exceedances in the summer are predominantly due to SO2emissions fiom large point sources, such as EGUs and other sources of direct PM2.5in the area, and that emissions from on-road motor vehicles are less important to the area's PM2.5problem during the summer. If an area chooses to establishmotor vehicle emissionsbudgets for one season of the year, it should use MOVES inputs and other data that

are relevant for the chosen season. In such a case, the resultingbudgets would be for a 24-hour period calculated in MOVES on an hourly basis.

Regardless of which approach is used, we recommend that the state base the motor vehicle emissions budgets on air quality data, including available speciation data from the years on which the SIP is based and any available modeling demonstration. Decisions on which approach to take should be made after consultation occursbetween states and local air and transportationagencies (including the metropolitan planning organization), the Federal Highway and Transit Administration local offices, and the EPA Regional Office.

approved version of AP-42 or other local method that has been approved by EPA. Emissions of dust from constructionof transportation projects would be calculated using AP-42 or other local method.

34 For additional guidance on creating daily emissions inventories, refer to EPA's guidance documents located at: http://www.e~a.gov/otaq/stateresources/index.htm.It is important to note that the regional emissions analyses for subsequent transportation conformity determinations would estimate emissions using inputs consistent with the inputs used to estimate the motor vehicle emissions budgets. For example, emissions for a regional emissions analysis would be calculated using winter MOVES inputs if the budgets for the area were established for the winter season.

Developing Non-Road Emission Inventories

Areas are required to provide estimates of emissions from non-road vehicles and equipment. The EPA recommends the use of the most recent version of the EPA's NONROAD model to estimate non-road emissionsin areas outside of ~alifornia.~~ It should be noted that some categories ofnon-road sources will have higher emissions during one season as opposed to the others. For example,in northern states, emissions from construction equipment are likely to be higher in the summer as compared to the winter. This seasonal variation should be accounted for in modeling inventories and in any other seasonal inventories that are prepared.



### Recommendations for 

### the 2006 24-hour 

### PMP Implementation Rule

Attainment Dates: Section 51.1004

Under section 172(a)(2)(A)ofthe CAA, an area's attainment date "shall be the dateby which attainment

canbe achieved as expeditiously as practicable, but no later than 5 years from the date such area was designated nonattainment 

## * * *

,except that the Administrator may extend the attainment date to the extent the Administrator determines appropriate, for a period no greater than 10 years from the date of designation as nonattainment considering the severity ofnonattainment and the availability and feasibility of pollution control measures." For PM2.5, a state's attainment demonstration should provide a thorough analysis of available control measures and provide a proposed attainment date supportedby the analysis. Under the 2007 PM2.5 Implementation Rule, analytical and regulatory requirements are more stringent for areas that are unable to demonstrate attainment within the first five years. The EPA believes that these same approaches are reasonable interpretations of the statute for the 2006 24-hour PM2.3NAAQS as well.

Because the designation ofnonattainment areas for the 2006 24-hour PM2.5 NAAQS became effective

on December 14,2009,the presumptive five-year attainment date for many areas would be no later than December 14,201 4, just two weeks short of the end of the calendar year. The form ofthe 24-hour PM2.5 NAAQS relies on evaluating three full calendar years of air quality data to calculate the design value for the area. To determine attainment, the EPA commonly uses the three most recent calendar years of complete air quality data that are available. Because calendar year 2014 would not be complete on December 14,2014,this could be read to suggest that control measures taking effect at the beginning of 2014, and the resulting air quality improvements, could not be considered in the attainment determination. However, we note that states can take 2014 into account in their attainment demonstrations,and the EPA will consider the approvability of attainment demonstration SIPSon a case-by-case basis. For example, an attainment demonstration that is intended to show attainment within

35 More information and guidance onNONROAD is available at: http://www.epa.~ov/otaq/nonrdmdl.htm. Information on emissionsfrom marine sources and locomotives are available at http://www.epa.gov/otaq/marine.htm and http://www.epa.gov/otaq/locomotives.htm,respectively. Areas in California should consult with EPA Region 9 to determine the appropriate model for estimating non-road emissions.five years of designation maybe approvable if control measures to reach attainment are scheduled to be operational at the beginning of 2014.~~ Under this example, this approach would provide states with the opportunity to use air quality data from 2012 through 2014 to assess attainment for the 2006 24-hour PM2.5 NAAQS.

One-YearExtension ofthe Attainment Date: Section 51.1005

Section 5 1.1005of the 2007 PM2.5 Implementation Rule describes the criteria governingwhen an area may apply for a one-year extension of the attainment date pursuant to section 172(a)(2)(C)(ii)ofthe CAA. The EPA believes that an appropriate interpretationofthis provision with respect to the 2006 24- hour PM2,5 NAAQS would be that if an area has a design value which exceeds the standard based on three consecutiveyears of air quality data, but the third year's data indicate improved air quality such that the PM2.5 concentration for that one year is below the level of the standard (e.g., the 98th percentile 24-hour concentration for that one year is equal to or less than 35 ug/m3),then the area has improving air quality and may apply to the EPA for a one-year extension of the attainment date.

The regulatory text ofthe 2007 PM2.5 Implementation Rule (seeparagraphs 51.1005(a)(2)and (b)(2)) provides that a state "may apply" for a one-year attainment date extension if the 98th percentile concentration for the previous year was equal to or less than the 1997 24-hour PM2.5 NAAQS of 65 ug/m3.With respect to implementing the 2006 24-hour PM2.5NAAQS, if states chooseto apply for a one-year extension, we recommend that they show that the area's 98th percentile concentration for the previous year is less than the 2006 24-hour PM2.5NAAQS, i.e., 35 ug/m3.

Emission Inventory Requirements: Section 51.1008

The regulatory text of section 51.1008(b)of the 2007 PM2,5 ImplementationRule states that "[Flor inventories required for submission under paragraph (a) of this section, a baseline emission inventory is required for the attainment demonstrationrequired under section 51.1007 and for meeting RFP requirements under section 5 1.1009.As determined on the date of designation, the base year for this inventory shall be the most recent calendar year for which a complete inventory was required to be submitted to the EPA pursuant to subpart A of this part. The baseline emission inventory for calendar year 2002 or other suitable year shall be used for attainmentplanning and 

### RFP plans for areas initially designated nonattainment for the PM2.5NAAQS in 2004-2005."

The overall intent of this provision is for states to use the best available informationin their analyses. States should use the most recently updated information when developing their emission inventories for the nonattainment area for use in their attainmentplans (and for RFP plans for any area that needs to submit one). For purposes of developingplans to attain the 2006 24-hour PM2.5NAAQS, the EPA believes that the statuteprovides adequate flexibilityto states to use the most recent "suitable year" for their analyses.

As mentioned earlier, if a seasonal inventory approach is followed, the EPA recommends that states give additional attention to refining emissions estimates for key source categories which operate predominantly during the relevant season (e.g., woodstoves in winter) in order to identify which

See EDF v. EPA, 369 F.3d 193 (D.C. Circuit 2004); Sierra Club v. EPA, 356 F3d (D.C. Circuit 2004) amended 2004 WL 877850 (D.C. Circuit 2004).emissions sources are contributing to the season-specific nonattainment. The emission inventory used for SIP purposes would pertain to the particular season in which exceedances occur for multiple years. If exceedances occur in more than one season, then we recommend that statesuse an annual inventory.

Reasonable Further Progress: Section 51.1009

This section addresses two issues related to RFP: the specific years for emission reduction milestones to be included in an RFP plan for the 2006 24-hour PM2.5 NAAQS; and the geographic region to be represented in the plan.

Milestone Years. Section 51.1009 of the 2007 PM2.5 Implementation Rule requires any area that submits

an approvable demonstration for an attainment date of more than five years from the effective date of designation to also submit an RFP plan. The 2007 PM2,5 Implementation Rule includes two approaches for demonstrating compliance with interim RFP milestones: eitherby showing that emission reductions provide for "generally linear progress," or alternativelyby showing that air quality improvement provides for "generally linear progress." The EPA believes this interpretation of the statute would also be appropriate for the 2006 24-hour PM2.5NAAQS. We recommend that the state develop an RFP plan that uses emission inventory information and related data consistent with what is used for the attainment demonstration.We further recommend that the plan includes emission reduction milestones showing that in each applicable milestone year, emissions will be at a level consistent with "generally linear progress" in reducing emissions between the base year and the attainment year.

Section 51.1 OO9(c)(l) of the 2007 PM2.5Implementation Rule requires that an area with an attainment date ofmore than 5 years and less than 9 years includes 2009 emission milestones for direct PM2.5 and PM2.5 attainment plan precursors. Section 5 1.1009(~)(2) states that an area with an attainment date of 9

or 10years from designation must include 2009 and 2012 emission milestones for direct PM2.5 and PM2.5 attainment plan precursors.

In other words, for the 1997PM2.5 NAAQS, the 2007 PM2.5Implementation Rule requires an area with

an attainment date of 6-8 years from the date of designation (i.e., 201 1 to 2013) to include an emission milestone in 2009. The 2007 PM2.5 Implementation Rule requires an area with an attainment date of 9 or 10years from the date of designation (i.e., 2014 to 2015) to include emission milestones in 2009 and in 2012. The EPA recommends that the framework ofthe 2007 PM2,5Implementation Rule and the associated plan submission timelines be similarly applied and interpreted in relative terms for purposes of developingRFP plans for the 2006 24-hour PM2.5 NAAQS.

Therefore, for purposes ofimplementation ofthe 2006 24-hour PM2.5NAAQS, EPA believes that it would be appropriate to apply an analogous framework. For an area with an attainment date of 6-8 years from the date of designation (i.e., 2015 to 2017 if the area was designated in 2009), under this interpretation the RFP plan would need a milestone for one interim year, in this case, 2014. For an area with an attainment date of 9 or 10 years from the date of designation (i.e., 2018 to 2019 if the area was designated in 2009), the RFP plan would need milestones for two interim years, 2014 and 2017. Thus, in reviewing implementation plans, submitted by areas that were designated nonattainment in 2009 for the 2006 24-hour PM2.5NAAQS, EPA intends to considerthe appropriate interim milestone years to be 2014 and (ifnecessary) 2017.

We recognize that each nonattainment area has its own unique characteristics (e.g., physical features, source population, seasonal nature of exceedances, types of emission reduction programs adopted)which will affecthow the area can demonstrate reasonable further progress toward attainment. Therefore, each RFP plan will be evaluated on a case-by-case basis.

GeographicRegion. Reasonable further progress is defined under CAA section 171 (1) to mean "such annual incremental reductions in emissions of the relevant air pollutant as are required by this part or may reasonablybe required by the Administrator for the purpose of ensuring attainment ofthe applicable national ambient air quality standard by the applicabledate." RFP for PM2.5is required under section 172. Section l72(c)(3) states that nonattainment area plans must include a comprehensive inventory of emissions from "all sources

. . 

### .in [thenonattainment] area." The 2007 PM2,5 Implementation Rule includesprovisions for calculating emissionreduction milestones using the base year and projected attainment year emission inventories for the relevant "geographic area" represented in the RFP plan. From the discussion of the geographic area in the preamble, one can infer that the default geographic area would be the nonattainment area. However, the preamble also includes discussion of a policy that allowed states to take credit for reductions ofNO, and SO2emissions up to 200 kilometers (krn) from outside the nonattainment area (and potentiallyfor reductions of VOC or ammonia as well) only when certain conditions are met, includingthat when taking RFP credit for emissionsreductions achieved outside of a nonattainment area, the baseline emissions inventoryfor the nonattainment area contain all, rather than a select few, sources in the outside area.

In 2007, the EPA received a petition for reconsideration of this policy for the 1997PM2.5NAAQS. In addition, in 2006, the EPA received a petition for reconsiderationof a similarpolicy in the implementation rule for the 1997 8-hour ozoneNAAQs." The petitions for both PM2.5 and ozone challengedthe allowance of emissionsreductions from outside of the nonattainment area for meeting RFP requirements.

Additionally, in 2009, the United States Court ofAppeals for the District of Columbia Circuit (the Court) examined the phrase "in the area" included in separate provisionsrelating to reductions from the application of RACT. In the Phase 2 Ozone Implementation Rule, EPA had explained that because an interstate emissions trading program would achievebeyond RACT-level NOxreductions regionally,

areas did not have to meet the RACT-level reductions required under CAA section 182(b)(2)solely from within the nonattainment area. The Court, however, concluded that the phrase "in the area" means that reductions must occur from sources within the area and "reductions from outside the nonattainment

area do not satisfy the requirement."38On December 22,201 0, (75 FR 80420),the EPA proposed a rule to reflect its reconsideration ofthe RFP policy for ozone. 

### In light of the Court decision emphasizing that "in the area" means in the nonattainment area and due to the proposed action for ozone, the EPA granted the petition for reconsideration ofthe RFP policy for PM2.5 on May 13,2010.

The EPA acknowledges that attainmentplans for some areas may include a certain level of emission reductions (and air quality improvement) from sources within the nonattainment area, and also a certain level of emission reductions (and air quality improvement) attributed to sources outside the nonattainrnent area. The EPA will be addressing this issue in responseto the petition for reconsideration pertaining to the 2007 PM2.5Implementation Rule. Therefore, for purposes ofmeeting the RFP

37 In the preamble to the Phase 2 Ozone Implementation Rule, EPA stated that credit could be taken for VOC and NO, emission reductions within 100km and 200 km, respectively, from outside the nonattainment area under certain circumstances.

38 SeeNRDC v. EPA, 571 F.3d 1245 at 1256 (D.C. Cir. 2009).requirement for the 2006 24-hour PM2.5NAAQS, states should rely only on emission reductions achieved from sources within the nonattainment area.

Contingency Measures: Section 51.1012

Contingency measures, required pursuant to section 172(c)(9) of the CAA, are emission reduction

measures that are to be undertaken by a state if the area fails to attain the NAAQS by its attainment date

or fails to make RFP toward attainment. These contingency measures must take effect without further actionby the state.

The preamble ofthe 2007 PM2,5 Implementation Rule (see 79 

### FR 20642-20645) notes that contingency

measures "should provide for emission reductions equivalent to about one year of reductions needed for reasonable further progress (RFP)." The term "one year of reductions needed for RFP" requires clarification. This phrase maybe confusing because all areas technically are not required to develop a separate RFP plan under the 2007 PM2.5 Implementation Rule. Thebasic concept is that an area's set of contingency measures should provide for an amount of emission reductions that would achieve "one year's worth" of air quality improvement proportional to the overall amount of air quality improvement
to be achieved by the area's attainment plan; or alternatively, an amount of emission reductions (for all pollutants subjectto control measures in the attainment plan) that would achieve one year's worth of emission reductions proportional to the overall amount of emission reductions needed to show attainment. Contingency measures can include measures that achieve emission reductions from outside the nonattainment area as well as from within the nonattainment area, provided that the measures produce the appropriate air quality impact within the nonattainment area.

The EPA believes a similar interpretation ofthe contingency measures requirements under section 172(c)(9)would be appropriate for the 2006 24-hour PM2.5 NAAQS. Included below is an example to illustrate this concept.

Assume that the area in question was designated nonattainment in December 2009 with a 2006- 2008 design value of 41 ug/m3. 

### 3 The SIP would be due in December 2012 and attainment would generally need to occur within five years, based on air quality data through December 2014.

Assume that the state analysis uses a 2008 base year emissions inventory and a future year projection inventory for 201 4. 

# + To demonstrate attainment, the area needs to reduce its air quality concentration from 41 ug/m3in 2008 to 35 ug/m3in 2014, equal to a rate of change of 1ug/m3 per year. The attainment plan demonstrates that this level of air quality improvement would be achievedby reducing emissions between 2008 and 2014 by the following amounts: 1,200 tons of PM2,5; 6,000 tons ofNOx;and 6,000 tons of SO2. 

### 3 Thus, the target level for contingency measures for the area could be identified in two ways: 1) The area would need to provide an air quality improvement of 1 ug/m3in the area, based

on an adequate technical demonstration provided in the state plan. The emission reductions to be achievedby the contingency measures can be from any one or a combination of all pollutants addressed in the attainment plan, provided that the state plan shows that the cumulative effect ofthe adopted contingency measures would result in a 1 ug/m3 improvement in the fine particle concentrationin the nonattainment area; and 2) The contingency measures for the area would be one-sixth (or approximately 17percent) of the

### overall emission reductionsneeded between 2008 and 2014 to show attainment.In this example, these amounts would be the following:200 tons ofPM2.5;1,000 tons ofNOx;and 1,000 tons of S02.

Questions Regarding This Guidance



### In general, questions may be directed to Rich Damberg at (919) 541-5592or damberg.rich@,e~a.nov; and Kristin Riha at (9 19) 541-2031 or riha.kristin(i3epa.m~. Specificquestions on transportation conformity shouldbe directedto Meg Patulski at (734) 214-4842 or patulski.men@,e~a.~ov. Any questions on the use of the MOVES model should be sent to: mobile@,epa.nov.

cc: Anna Wood, OAQPS Lydia Wegman, OAQPS Richard Wayland, OAQPS Greg Green, OAQPS Peter Tsirigotis, OAQPS Margo Oge, OTAQ Karl Simon, OTAQ Sarah Dunham, OAP