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Environmental Protection Agency (EPA): Proposed Rule

Fine Particulate Matter (PM2.5) National Ambient Air Quality Standards (NAAQS):

State Implementation Plan (SIP) Requirements

RIN 2060-AQ48

General Comments

1. Wildfire and wildland fire.

a. Commenters recommend including additional context and background in the 

preamble and rule language about prescribed fire (planned ignitions) and wildfire 

(unplanned ignitions). Specifically, that not including prescribed fire and wildfire

may unintentionally set a precedence that limits the options for managing 

wildland fire, limits the role of wildland fire in restoring and maintaining resilient 

landscapes, preclude options for effective management of carbon, and 

inadvertently violate the direction set forth in Executive Order (EO) 13653.

Response: We understand the commenter’s interest in providing more context for 

fire related issues. The text below was adapted from language to be included in 

the final 2008 ozone SIP requirements rule, and we recommend adding it as a 

footnote on page 16, following table 1, which describes national emissions by 

sector.

“It should be noted that the “miscellaneous” sector has the highest level of estimated 

PM2.5 emissions primarily due to emissions from wildfire. Wildfire emissions can 

significantly contribute to periodic high PM2.5 levels. Besides their effect on air 

quality, wildfires pose a direct threat to public safety – a threat that can be mitigated 

through management of wildland vegetation. Attempts to suppress wildfires have 

resulted in unintended consequences, including increased risks to both humans and 

ecosystems. The use of wildland prescribed fire can influence the occurrence of 

catastrophic wildfires which may help manage the contribution of wildfires to PM2.5

concentrations. Additionally prescribed fires can have benefits to those plant and 

animal species that depend upon natural fires for propagation, habitat restoration, and 

reproduction, as well as myriad ecosystem functions (e.g., carbon sequestration). The 

EPA understands the importance of prescribed fire which mimics a natural process 

necessary to manage and maintain fire-adapted ecosystems and climate change 

adaptation, while reducing risk of uncontrolled emissions from catastrophic wildfires, 

and is committed to working with federal land managers, tribes, and states to 

effectively manage wildland fire use to reduce the impact of wildfire related 

emissions.”

2. Precursor policy options.

a. Commenter recommends considering hybrid approaches to addressing regulation 

of PM2.5 precursors in attainment plans and nonattainment new source review 

(NNSR). Specifically, one hybrid approach could have Option 2A as a screening 
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mechanism for whether a particular PM2.5 precursor is important or a significant 

contributor to nonattainment in the area, and if so, Option 3 could then be utilized 

to demonstrate that control measures for all types of sources of a particular 

precursor are not needed for expeditious attainment of that area.

Response: The precursor policy options in the proposed rule start from EPA’s 

interpretation of the statute that all precursors are to be addressed in attainment 

planning and NNSR unless the state provides an adequate demonstration showing 

that a particular precursor is not significant. Note that the three draft options are 

presented broadly in order to elicit a wide range of comments that can be 

considered for developing the final rule. 

The suggested hybrid option proposes a combination of options 2A and 3. Option 

2A would allow the state to provide a technical demonstration showing that all 

emissions (i.e., from area, mobile, and stationary sources in the area) of a 

particular precursor collectively do not provide a significant contribution to PM2.5

levels that exceed the standard in the area. Option 3 states that an attainment

planning (i.e., RACM and RACT) analysis demonstrating that control measures 

for all types of sources of a particular precursor are not needed for expeditious 

attainment also would be deemed to meet the section 189(e) technical 

demonstration requirement, meaning that the state would not need to regulate 

emissions of the particular precursor from major stationary sources under the 

NNSR permitting program or impose other control requirements for major 

stationary sources. Note that under option 2A, if an adequate demonstration is 

made, then the state would not need to evaluate control measures for attainment 

planning purposes or for NNSR for that particular precursor. Thus, Option 2A 

would achieve a similar result to what the commenter seems to be advocating for 

by suggesting a hybrid of Options 2A and 3. For this reason, we do not see the 

need to present a specific option 2A-option 3 hybrid, but we have modified the 

last paragraph of the precursor policy section on page 80 to acknowledge the 

possibility of considering a hybrid approach: 

“The EPA also seeks comment on whether only one of these approaches should 

be included in the final rule, or whether it would be appropriate to include 

multiple approaches (e.g., both Options 1 and 2) or a hybrid of two approaches by 

which a state could demonstrate that a particular precursor would not need to be 

addressed in the attainment plan or permitting program for a specific area.”

3. De minimis determination.

a. Reviewer recommends providing an alternative for “safe harbor” type provisions 

for de minimis determinations. The alternative would state that if the contribution 

is below a certain percentage (e.g., 3 percent) it would be considered de minimis

and an amount greater than that percentage would require additional justification 

to determine that the contribution is de minimis.
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Response: The concept of de minimis is already presented in the proposal in two 

ways: with regard to emissions of a particular precursor, and with regard to 

emissions from a particular source category; and with each proposed approach, 

there is a “no threshold” option and an option in which de minimis could be 

considered to be up to 3% of the relevant standard. 

On page 131, EPA requests comment on several questions, which indicate the 

complexity of this issue:

“The EPA is requesting comment on the appropriateness of including de minimis

threshold options for exempting certain source categories from consideration for 

reasonable control measure determinations, and seeks input on the following 

questions: If a de minimis threshold is included, what is the appropriate definition 

for source categories? What are the appropriate thresholds for impacts on ambient 

PM2.5 concentrations that would adequately reflect presumptive de minimis

concentrations from a given source category comparable to those recommended 

for purpose of the PM10 NAAQS? Should the de minimis source category 

thresholds be a percentage of the relevant NAAQS (i.e., similar to what was 

recommended for PM10 but set at a level that is more appropriate for the level and 

form of the relevant NAAQS)? The EPA requests that commenters submit any 

relevant data or analyses to support their comments with respect to these issues.

Furthermore, the EPA notes that even in the event the agency finalizes this 

rulemaking with a de minimis source category policy of any kind, states are 

obligated under the CAA to demonstrate how their PM2.5 nonattainment area will 

attain the standard as expeditiously as practicable. Accordingly, a state could not 

elect to treat source categories as de minimis if doing so would prevent the state 

from being able to demonstrate attainment for the area by the statutory attainment 

date.”

The presentation of these two approaches to de minimis determinations, and two 

options per approach, already introduces a fair degree of complexity to this concept. 

The policy space that is “defined” by the options is broad enough to include 

consideration of other options suggested by commenters. We believe the addition of a 

third option to each of the two approaches to de minimis in the proposal will add too 

much complexity, and for this reason we decline to change the proposal as suggested 

by the reviewer.

4. Base year.

a. Reviewer recommends considering additional years as the base year for 

attainment plans and determinations; including providing additional discussion as 

to why the Air Emissions Reporting Rule (AERR) should not be used as a base 

year.

b. Response: As described on page 100, there is great flexibility in the inventory 

year. The inventory year must be one of the 3 years used for designations or 
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another technically appropriate year. The specific circumstances for which 

another year could be appropriate are provided. Since the AERR is collected on a 

triennial schedule, an AERR year would always be available as an option under 

this approach, provided that an AERR year is appropriate considering other 

factors, such as meteorology, that should be considered for selecting a year in the 

event an attainment demonstration is needed. For these reasons, we do not believe 

additional changes are needed to this section.

5. North American Industry Classification System (NAICS).

a. Reviewer recommends providing additional discussion on the differences in 2, 4, 

and 6 digit codes and why 4 digit codes are the most appropriate.

Response: We added the discussion below to page 129. It was taken from the 

Census Bureau webpage at: 

http://www.census.gov/eos/www/naics/faqs/faqs.html#q5

“NAICS is a 2- through 6-digit hierarchical classification system, offering five 

levels of detail. Each digit in the code is part of a series of progressively narrower 

categories, and the more digits in the code signify greater classification detail. The 

first two digits designate the economic sector, the third digit designates the 

subsector, the fourth digit designates the industry group, the fifth digit designates 

the NAICS industry, and the sixth digit designates the national industry. The 5-

digit NAICS code is the level at which there is comparability in code and

definitions for most of the NAICS sectors across the three countries participating 

in NAICS (the United States, Canada, and Mexico). The 6-digit level allows for 

the United States, Canada, and Mexico each to have country-specific detail. A 

complete and valid NAICS code contains six digits.”

We also revised the following sentence later on the same page: 

“For this reason, the EPA proposes and seeks comment on a requirement that a 

state would need to define any source category for which a NAICS code exists at 

the four-digit industry group level. The EPA believes that relying on the four-digit 

industry group level to define “source category” for this purpose would provide 

an appropriate degree of distinction between industrial processes while not 

making the source category definition overly broad. The EPA also seeks comment 

on two other alternative approaches for defining source category for this purpose,

at the six-digit level, and the two-digit level.”

6. Use of previous reasonably available control measures (RACM) and reasonably 

available control technology (RACT).

a. Reviewer recommends evaluating a “recent threshold” (e.g., within 3 years of 

when this RACM/RACT is performed) that would allow either no updates or a 

less extensive update to RACM and RACT.
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Response: We do not believe the statute authorizes EPA to establish a presumption that 

any RACM/RACT determination made in the past 3 years automatically is adequate for 

this new SIP. The state would still need to present its case that additional control is not 

technologically and/or economically feasible and that the recent determination represents 

RACM/RACT for the new SIP, and we would expect that in many cases, a determination 

made in the past 3 years would be adequate. To address this comment, we recommend 

adding the underlined text to page 133:

“The EPA recognizes that for some sources located in a Moderate PM2.5 nonattainment 

area, a state may have previously conducted RACM and RACT analyses to address 

emissions for other statutory purposes. Some of the RACM and RACT determinations 

could be relatively recent, while other determinations may be 15 years old or older. The 

EPA proposes that a state may not simply rely on a previous RACM or RACT 

determination for a particular source or source category when developing the attainment 

plan for a PM2.5 NAAQS, but rather that the state must consider all existing and potential 

new measures together as part of a comprehensive RACM and RACT analysis. In this 

way, the state’s new RACM and RACT analysis will represent the most thorough, up-todate review of control measures for its PM2.5 nonattainment area. For example, the state 

would still need to provide a RACT analysis for a source that has installed new emission 

controls recently (e.g. within the last three years), but the state’s determination may 

consider that recent installation when determing whether additional control is 

economically and technologically feasible.”

7. Technical feasibility determination. (140)

a. Commenter recommends clarifying that for agricultural sources that mitigation 

measures that may be technically feasible for one agricultural source may not be 

technically feasible for a similar type of agricultural operation.

Response: We believe that the existing text provides sufficient flexibility to allow 

a state to present information describing why one emission reduction approach 

would be technically feasible at one specific source while it would not be 

technically feasible at another source. We decline to add specific language 

regarding agricultural operations because this rule is intended to provide broad 

guidance that applies to a wide range of states and source types, providing as 

much flexibility as possible under the statute for air agencies to determine an 

appropriate control strategy for their PM2.5 nonattainment areas but without 

providing specific guidance for each potential type of source category that could 

be addressed in a SIP. For this reason, we have not included source-category 

specific statements in the preamble, and believe we should maintain this 

approach.

8. Economic feasibility determination.

a. Reviewer recommends clarifying whether sources with similar technological 

characteristics owned by different sized entities are considered “similar sources” 

with respect to economic feasibility or would a state be allowed to justify 
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rejection based on the size of entities applying such technology. EPA states that a 

state may not reject technologically feasible measures as economically infeasible 

if similar sources have implemented the technology, absent adequate justification. 

Therefore, while a state may consider engineering criteria to evaluate 

technological feasibility, small entities could be required to install economically 

infeasible technologies solely because a similar source owned by a larger facility 

has install the technology.

Response: States have flexibility to determine appropriate RACM, including 

RACT, based on a full evaluation of the “feasibility” aspect of “reasonably 

available.” Proven technologies or measures may not be economically feasible or 

cost effective in every potential application. The preamble specifically allows a 

state the discretion to decline to require the control if it is able to provide an 

adequate justification for the differing treatment. In addition, we have added the 

underlined text to the sentence on page 141 to help clarify what is meant by the 

term “similar source”:

“Furthermore, the EPA proposes that a state may not reject a technologically 

feasible control measure or technology as being economically infeasible if such a 

measure or technology has been implemented at other similar sources (i.e., at 

sources that would be included in the same source category in the emission 

inventory data collection process), unless the state provides an adequate

justification that clearly explains the specific circumstances of the source or 

sources in the nonattainment area that make such a measure or technology 

economically infeasible in that particular area.”

We also note that later in this section (page 142), there is language enabling a 

state to provide information to demonstrate why an entity should not be 

considered to be able to afford a particular control measure used on similar 

sources. The language reads as follows:

“In addition, if a state contends that a source-specific control-level should not be 

established because the source(s) cannot afford the control measure or technology 

that is demonstrated to be economically feasible for other sources in its source 

category, the EPA proposes that the state must support the claim with information 

regarding the impact of imposing the identified control measure or technology on 

the following financial indicators, to the extent applicable:

1. Fixed and variable production costs ($/unit)

2. Product supply and demand elasticity

3. Product prices (cost absorption vs. cost pass-through)

4. Expected costs incurred by competitors

5. Company profits

6. Employment costs

7. Other costs (e.g., for RACM implemented by public sector entities).
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The EPA seeks comment on the factors described above for states to 

consider when determining whether a control technology or measure is 

economically feasible.”

A reviewer has recommended that two additional factors be added to this list: 8. 

Impact on jobs and 9. Cumulative impacts to the source not considered above 

(e.g., delays in maintenance or other potential safety-related actions).

This list of factors is taken from long-standing guidance (the 1992 General 

Preamble) that is applicable to implementation of more than just the PM NAAQS. 

A reviewer has recommended that two additional factors be added to this list: 8. 

Impact on jobs and 9. Cumulative impacts to the source not considered above 

(e.g., delays in maintenance or other potential safety-related actions). We think 

the guidance has proven sufficiently broad and has provided adequate flexibility 

to states to be able to present reasoning to demonstrate why certain facilities are 

not able to afford control technology used on similar sources. Changing the 

longstanding guidance risks introducing confusion to states in their attainment 

planning process with little potential gain in return. 

b. Reviewer recommends evaluating whether “safe harbor” type provisions for 

economic feasibility with respect to cost effectiveness are appropriate.

Response: The proposed rule intentionally does not include a safe harbor 

provision or bright line with respect to what cost effectiveness level would be 

considered appropriate or inappropriate under all circumstances. The reason for 

this is that every nonattainment area is different, and some areas have more 

serious air quality problems than others. In order to attain the standard and protect 

public health sufficiently in these areas, control measures may need to be adopted 

in the state that have higher per ton levels than control measures needed to attain 

for areas with less serious air quality problems. 

9. Attainment demonstration. (173)

a. Reviewer recommends providing benefits and costs of each of the proposed 

alternatives for the attainment demonstration. For example, discuss the relative 

level of risk of just using FRM and/or FEM monitoring data.

Response: (We assume this comment addresses the options for addressing 

unmonitored areas in the attainment demonstration.) The occurrence of potential high 

PM2.5 concentrations in unmonitored areas is by definition unknown and cannot be 

evaluated without completing a case-by-case analysis for each nonattainment area. It 

is therefore not possible at this time to calculate the benefits and costs of each of the 

proposed attainment demonstration alternatives. 

That said, we can make some qualitative observations. For example: Option 1, which 

requires attainment to be shown only at monitoring locations, would be expected to 
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be the least costly option to implement. Option 2, which would require the state to 

conduct an unmonitored area analysis as part of all attainment demonstrations and 

require the state to eliminate potential violations in unmonitored areas through 

enforceable emissions reductions in the SIP, could potentially lead to additional 

control costs. However, any additional control costs would be accompanied by 

concurrent additional health benefits. The magnitude of these potential costs and 

benefits would vary on a case-by-case basis.

Since we are unable to estimate the potential costs and benefits of the various options 

in a meaningful way, we do not believe additional preamble language would help 

provide useful information to the reader to help decide between the options. We 

therefore are not making any changes to the preamble language.

10. Credits for outside of nonattainment area for reasonable further progress (RFP).

a. Reviewer recommends providing additional discussion why EPA thought it was 

appropriate to allow up to 200 kilometers (km) away from the nonattainment area 

for RFP in the 2007 PM2.5 Implementation Rule and does not believe that it is still 

appropriate.

Response: We plan to add clarifying text to page 199 to explain the issue more 

clearly and fully, and to make it consistent with EPA’s approach to RFP and 

treatment of sources outside the nonattainment area in the upcoming final 2008 

ozone SIP requirements rule.

b. (196) Reviewer recommends considering credits outside of the nonattainment 

area for RFP because the EPA is requiring the use of outside the nonattainment 

area actions as “additional reasonable measures” to have a nonattainment area 

achieve attainment as expeditiously as possible and is allowing the use of outside 

the nonattainment area actions (but still within the state) as contingency measures 

within the SIP. For example, if the nonattainment area needs to decrease 

emissions by 6 percent over a 6 year period, for a linear a RFP, the nonattainment 

area would need to decrease by 1 percent a year. However, if because of the 

“additional reasonable measures,” the nonattainment area can demonstrate 

attainment within 4 years, the nonattainment area would need to decrease 

emissions by 1.5 percent a year. But because a state cannot credit outside the 

nonattainment area for RFP, the state may not be able to meet their RFP 

requirements. 

Response: If a state implements additional reasonable measures, and those 

measures include emission reduction strategies on sources located outside the 

nonattainment area, and these would advance the attainment date from 6 years to 

4 years, then the reduction obligation for the first four years for the sources within 

the nonattainment area (i.e., the reductions that are the basis for establishing 

RFP) would likely be the same or reduced, as compared to a scenario where the 

attainment strategy relied strictly on reductions from sources within the 
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nonattainment area. The most important issue in this hypothetical scenario is that 

the additional reasonable measures would lead to attainment a full two years 

sooner. By attaining the standard in the area that much sooner, significant health 

benefits would be realized in the nonattainment area. With air quality improving 

due to the additional reasonable measures, as well as from reductions from 

sources within the nonattainment area, it is possible that sources in the 

nonattainment area would not need to reduce emissions to the same degree. In any 

case, however, it would seem likely that EPA would have the flexibility under the 

implementation rule for PM2.5 (in contrast to the ozone implementation program, 

which has certain statutory percent reduction requirements for emissions within 

the nonattainment area) to find that the reductions that are anticipated from 

sources in the nonattainment area would be considered to provide for “generally 

linear progress” toward attainment. 

c. (145) Reviewer recommends providing additional basis and clarification for the 

term “additional reasonable measures,” including whether this term has been 

defined or used in other criteria pollutants of the Clean Air Act. If the term has 

not been previously used, the reviewer recommends explaining why PM2.5 is 

different than the other criteria pollutants that this requirement should be added. 

Response: Subpart 4 requires attainment for Moderate areas by the end of the 6th

year after designation, yet requires RACM to be submitted by the end of the 4th

year. (If designations take effect early in the calendar year, as is the case for the 

recent designations under the 2012 standard, then the time period from the 

effective date of designation to the attainment date could be close to seven years.) 

The term “additional reasonable measures” has not been defined previously for 

PM10 or for ozone, but the term is being introduced in the draft PM2.5 

implementation rule to make it clear that if there are other potential control 

measures other than RACM/RACT that are feasible and cost-effective, could be 

implemented between the end of the 4th year and the attainment date, and are 

needed for the area to attain by the attainment date, then the state is required to 

adopt them. One reason that the ozone and PM10 programs have not included the 

“additional reasonable measures” term in past implementation guidance may be 

because both programs have had specific requirements for EPA development of 

control measures guidance documents for specific key source categories. For 

ozone, there are more than 30 control techniques guidance (CTG) and alternative 

control technology (ACT) documents that have been developed for reducing VOC 

emissions. For PM10, section 190 of the CAA included requirements for EPA to 

develop guidance by 1992 on controlling key PM10 sources of concern (that were 

prevalent in certain areas in the late 1980’s) such as wood smoke, fugitive dust, 

and prescribed fire. There is no additional obligation for EPA to develop control 

measure guidance for specific PM2.5 source categories. However, the ”additional 

reasonable measures” provision will require states to adopt and implement control 

measures that cannot come on-line until years 5 or 6 after designation if such 

emission reductions are needed to attain the standard expeditiously. 
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11. Electronic submissions for RFP.

a. Reviewer recommends strengthening the language in the use of electronic 

communication and an electronic reporting system.

Response: We have modified the text on page 209 to address this comment:

“The EPA stated in the Addendum that the milestone report must be submitted from the 

Governor or Governor’s designee to the Regional Administrator of the respective EPA 

Regional Office serving the submitting state, and that the EPA will notify the state of its 

determination (regarding whether or not the state’s report is adequate) by sending a letter 

to the appropriate Governor or Governor’s designee. The EPA believes that given the 

improvements in electronic communication in the intervening years since the Addendum 

was issued, it would be appropriate to provide an electronic reporting capability or 

system for such milestone reports that simplifies the process and reduces resource burden 

on all sides. The EPA is investigating how to institute such a system, seeks comment on 

how electronic reporting could facilitate a state’s submittal of the required milestone 

report, how it could accommodate the various narrative and data-dependent components 

that the EPA is proposing be part of such a submittal, and what system features would be 

recommended by commenters.”

12. Extensions for attainment.

a. (221, 235) Reviewer recommends providing additional explanation of the 

difference between the attainment determinations in the previous PM2.5

Implementation Rule and this proposed rule and examples of specific cases where 

an extension would be needed and granted.

Response: We assume this comment refers to section J, attainment date 

extensions. We believe the preamble provides sufficient clarity on attainment date 

extensions for Moderate and Serious areas, so we do not recommend making any 

changes to the document. However, below we provide additional explanation to 

address the reviewer’s concerns: 

This section of the preamble describes the situation for an area that has reached its 

attainment date, and the area’s 3-year design value is above the level of the 

standard, but the value for the third year is below the level of the standard. Under 

these circumstances, a Moderate area would be eligible to receive a one-year 

attainment date extension. If the air quality concentration during the next year 

after receiving the extension is also below the level of the standard, the area can 

receive a second one-year extension. Note that these one-year extensions are only 

provided for Moderate areas, and the statute requires an evaluation of current air 

quality before an extension may be granted. 
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After an area is reclassified as Serious, it must then provide a new attainment 

demonstration showing that it will attain the standard within ten years of initial 

designation. If it identifies available control measures and conducts an 

assessment to determine whether it can attain by the end of year 10, and it 

determines that it cannot attain by the end of year 10, then the plan must also 

include an analysis to show by what year it can attain. Under these circumstances, 

the CAA allows the state to submit a request for a Serious area attainment date 

extension of up to an additional five years. Note that in contrast to the Moderate

area one-year extension provision (which requires an evaluation of current air 

quality data), the Serious area attainment date extension is requested in advance

based on the state’s attainment demonstration analysis of what would be its most 

expeditious future attainment date. The statute does not have a one-year 

attainment date extension provision for Serious areas. 

b. Reviewer recommends providing additional clarification on the difference in plan 

submittals between a Moderate nonattainment area plan and Serious 

nonattainment area plan for granting an extension.

Response: Please see response above.

13. Attainment date for Serious nonattainment areas.

a. Reviewer recommends clarifying that “10 years after designation” is as of 

“nonattainment” and should not be considered as of designation as of Serious 

nonattainment.

Response: We provide here a clarification between the term “designation” and 

“classification.” The proposal has used the term “designation” or “initial 

designation” to mean the process that occurs within 2-3 years after the NAAQS is 

revised to designate areas as attainment or nonattainment. The statute requires all 

areas that have been initially designated as nonattainment for PM2.5 to be 

“classified” as Moderate. When a Moderate area fails to attain the standard by the 

end of the 6th year after it was initially designated as nonattainment, the area is 

then “reclassified” as Serious. (It is not “designated” as Serious.) 

To address this comment, we have slightly modified the relevant sentence on page 

304:

“For example, for a Serious nonattainment area, a future case scenario for the year 

2025 (10 years after the initial nonattainment designation) is needed to examine 

whether the measures identified by the state would result in attainment.”

14. Emission inventory.

a. Commenter recommends developing a mechanism to allow for the use of 

emissions estimating methodologies (EEM) for animal production operations 
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under the National Air Emissions Monitory Study (NAEMS) when they become 

available.

Response: The current draft proposed rule already promotes the use of the best 

available data, which would include EEMs based on the NAEMS data if and 

when such methodologies become available for estimating emissions from animal 

production operations. As described on page 98, CAA section 172(c)(3) requires 

a “comprehensive, accurate, and current inventory of actual emissions,” and the 

preamble further stresses that the “specific attainment plan requirements for the 

PM2.5 NAAQS set forth in section 189(a) and associated modeling requirements 

make an accurate and up-to-date emissions inventory a critical element of any 

viable attainment plan.” The current draft also continues on page 98 to say that 

“States should use the best available, current emissions inventory information for 

attainment plan development, because high quality emissions inventory data are 

essential for the development of an effective control strategy.” Thus, it should be 

evident (without explicitly providing the suggested details in this rule) that new 

approaches such as the future EEMs using NAEMS data would be an option when 

such methodologies become available.

Furthermore, there are countless other emissions categories and countless 

associated emissions estimating approaches that could be used for estimating the 

emissions from these sources. To ensure that the approaches remain flexible and 

up-to-date, the emissions inventory guidance has traditionally been the place to 

address such specific recommendation methodologies, and this is the approach 

that we recommend in this case as well. It is unnecessary and infeasible to address 

all of the current and possible future approaches for every source category in this 

rulemaking notice, nor would we do so for a single source category.

15. Emission inventory decrease for Serious nonattainment areas that have failed to 

achieve attainment.

a. Reviewer recommends providing clarification on EPA’s determination process for 

determining if a Serious nonattainment area that fails to attain has decreased 

emissions by 5 percent each year.

Response: We have added the following paragraph on page 349 to clarify that 

quantitative milestone reporting would be used to track compliance with the 5% 

annual emission reduction requirement. We acknowledge that annual tracking of 

emissions is highly resource-intensive and therefore difficult for states. 

“The section 189(d) requirement to reduce emissions by 5% per year is in effect a 

fixed level of reasonable further progress to be achieved annually. Accordingly, just 

as quantitative milestones are used to track progress with RFP requirements, it is 

proposed that the state would be required to submit quantitative milestone reports to 

describe the area’s progress in meeting the 5% annual emission reduction requirement 

under section 189(d). See section VII.G for more details.”
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b. Reviewer recommends providing additional clarification of the “most recent 

inventory” in relation to Clean Air Act (CAA) section 189(d). If a state is 

required to calculate the inventory for the nonattainment area each year to 

determine if the nonattainment area has decreased emissions by 5 percent, does 

the 5 percent change to that year’s inventory or is it 5 percent of the initial 

inventory calculated?

Response: To provide additional clarification, we have revised the text on page 344 

as follows:

‘The statute requires that the requisite minimum 5 percent emissions reductions must 

be calculated from the total emissions for each precursor and for direct PM2.5

contained in the most recent inventory for the area, as described earlier in this section. 

In addition, the EPA proposes that these required reductions must then be achieved 

every year between the section 189(d) plan submission date and the new projected 

attainment date for the area. For example, assume it is 2025, and a Serious area has 

failed to attain the standard within 10 years of designation. Assume also that the most 

recent inventory available for an area subject to section 189(d) is for the year 2023. 

The 2023 inventory would serve as the base inventory for determining the emission 

reduction requirement under section 189(d). If the 2023 inventory indicates that 

emissions of direct PM2.5 from all sources in the area are 100 tons/day, then the area 

would need to reduce emissions of direct PM2.5 by 5% of the base inventory (in this 

example, 5% of the 2023 base inventory, or 5 tons/day) each year until the area 

attains the NAAQS. Thus, in the first year following submission of the section 189(d) 

plan for the area, emissions of direct PM2.5 could not exceed 95 tons/day; in the 

second year, emissions could not exceed 90 tons/day, and so forth.’

c. (351) Reviewer recommends clarifying that contingency measures that include 

outside the nonattainment area measures can be included for reaching the 5 

percent required level as long as those measures are quantifiable, enforceable, 

replicable, and accountable.

Response: The section 189(d) requirement to reduce emissions by 5% per year 

expressly applies to sources “in the area” (i.e. sources in the nonattainment area 

inventory). For this reason, emission reductions occurring outside the 

nonattainment area cannot be “credited” toward meeting the 5% per year emission 

reduction obligation. In addition, the 5% annual reductions after failure to attain 

are separate from any contingency measures that may have existed for failure to 

attain or meet reasonable progress requirements for earlier years.

16. Quantitative milestones.
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a. Reviewer recommends allowing a nonattainment area that has decreased 

emissions by greater than 15 percent within a 3 year period to carryover that 

additional decreased emission to the next quantitative milestone. 

Response: To address this comment, we have added the sentence below to the 

paragraph on page 345: 

“Although section 189(d) requires that a state develop measures that will obtain 

annual emissions reductions of “not less than 5 percent” from the most recent 

inventory, the EPA interprets this language to authorize states to elect to front-load 

emissions reductions in earlier years and still meet the 5 percent per year requirement. 

The EPA believes that interpreting the statute in this way will encourage states to 

implement measures earlier, where possible, rather than delay implementation of 

measures merely to assure that the 5 percent requirement can be met in later years. 

Early reductions of this kind would also be accounted for in state submittals to show 

they are meeting quantitative milestones every three years. Consistent with its past 

action to approve a Serious area nonattainment plan for the San Joaquin Valley (CA) 

PM10 nonattainment area under section 189(d), the EPA therefore proposes and seeks 

comment on an approach to allow states to carry forward any emissions reductions 

beyond the required minimum 5 percent in a given year to the next year as a means to 

encourage states to achieve emissions reductions as quickly as possible.1

17. Contingency measures for Serious nonattainment areas that have failed to attain.

a. Reviewer recommends clarifying why contingency measures should be required 

when those contingency measures would have already been instituted for failure 

to meet the RFP for the Serious nonattainment area.

Response: Section 172(c)(9) of the CAA requires contingency measures to be 

implemented if an area fails to meet RFP or fails to attain the standard: 

“(9) Contingency measures. Such plan shall provide for the implementation of 

specific measures to be undertaken if the area fails to make reasonable further 

progress, or to attain the national primary ambient air quality standard by the 

attainment date applicable under this part. Such measures shall be included in the 

plan revision as contingency measures to take effect in any such case without 

further action by the State or the Administrator.”

If the state is required to implement contingency measures for failure to meet 

RFP, it must establish new contingency measure in case it later fails to attain the 

standard or demonstrate RFP. The state should be able to institute new 

contingency measures before the next event that may trigger a requirement to 

implement such measures.

 

1

69 FR 30006 (May 26, 2004).
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18. Time-frame for attainment for Serious nonattainment areas that have failed to 

demonstrate attainment.

a. Reviewer recommends providing additional clarification why 5 years (consistent 

with CAA section 172(a)(2)) should be followed for demonstrating attainment 

and why EPA is not considering 6 or 10 years for demonstrating attainment 

(consistent with CAA section 188(c)(1) and (2) that are specifically related to 

PM).

Response: Changes have been added to this paragraph on page 357 to address 

this comment: 

“As previously discussed, section 189(d) requires a minimum 5 percent 

annual reduction in emissions of direct PM2.5 and PM2.5 precursors until the area 

attains the relevant NAAQS. However, neither section 189(d) nor other sections 

in subpart 4 explicitly establish or provide the authority to establish a new 

attainment date for the area; and other Subpart 4 attainment date provisions for 

Moderate or Serious areas are not applicable to areas in this situation. Therefore, 

once an area is beyond the attainment dates that Congress specified in subpart 4 

for the PM10 NAAQS, the EPA must look to the existing provisions of the CAA 

to provide authority for a new attainment date. Sections 179(d)(3) and 172(a)(2) 

provide generally applicable attainment dates that fill the gap in the statute left for 

areas subject to the requirements of section 189(d). Thus, for a PM2.5

nonattainment area subject to section 189(d), the EPA must establish a new 

attainment date, and must do so according to the provisions of section 179(d)(3) 

and 172(a)(2). EPA has followed this same approach in the past for PM10

nonattainment areas governed by subpart 4 nonattainment requirements.”

Footnote added here: For example, see the Federal Register notice from June 6, 

2007 (72 FR 31183) in which EPA finds that the Phoenix PM10 Serious 

nonattainment area failed to attain the standard by the 2006 attainment date. The 

notice states that the new attainment date is established under section 179(d)(3).

19. Definition of stationary source.

a. Commenter recommends providing additional explanation and guidance of how 

stationary sources relate to agricultural production operations.

Response: We do not believe that it would be appropriate to revise the draft preamble to 

provide “explanation and guidance of how stationary sources relate to agricultural 

production operation” in light of ongoing commitments and agreements EPA already has 

in this area. As you know, we currently have an Air Quality Memorandum of 

Understanding with the USDA in which EPA will work in cooperation with the USDA in 

developing relevant national policy and guidance documents regarding agricultural 

production operations. In addition, EPA has a consent agreement with animal feeding 

operations (AFOs) to conduct a nationwide study to establish a better understanding of 
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the AFO air emissions so that the EPA could publish emission-estimating methods for 

AFOs. 

20. Major source thresholds for PM2.5 precursors. (380)

a. Reviewer recommends modifying EPA’s policy on preferred ratios for major 

source threshold determinations for PM2.5 precursors related to sulfur dioxide 

(SO2) and nitrogen oxides (NOX). Specifically, the EPA believes that the 

preferred ratios in the 2008 PM2.5 NSR Rule were not conservative enough (page 

374). However, not considering the relative effect of PM2.5 precursors to direct 

PM2.5 puts an undue burden on potential sources of PM2.5 precursors and sets a de 

facto more protective air quality standard than for direct PM2.5 sources.

Response: It is not clear what is meant by “modifying EPA’s policy on preferred 

ratios for major source threshold determinations....” As explained in the draft 

preamble, the policy on preferred ratios that the EPA set forth in the 2008 PM2.5 

NSR Implementation Rule was developed “for purposes of interpollutant offset 

trading, whereby a source could obtain reductions of a PM2.5 precursor to offset 

an increase of direct PM2.5 emissions or another PM2.5 precursor based on the 

“preferred” offset ratios.” Arguably, such ratios, if approvable, could potentially 

also have been applied to the setting of major source thresholds for the individual 

PM2.5 precursors. However, we indicated in a subsequent 2011 memo that we 

could no longer support the preferred offset ratios as being presumptively 

approvable in state implementation plans.2 Similarly, while we generally agree 

with the comment that precursor thresholds should reflect the relative effect of the 

individual precursor on ambient PM2.5 levels, we do not currently have a

sufficient technical basis to prescribe specific higher thresholds by rule. We 

believe that the preamble adequately explains the technical and legal impediments 

and requests public comments as to how to best address this issue. 

b. (376) Reviewer recommends adding a discussion of whether volatile organic 

compounds (VOC) and ammonia (NH3) emissions (the other PM2.5 precursors not

mentioned above) should be considered at higher levels than direct PM2.5 for 

major source thresholds.

Response: The preamble discussion is written so that it pertains to all PM2.5 

precursors. NOx and SO2 are specifically mentioned in one segment of the discussion 

 

2 See memorandum from Gina McCarthy, EPA Assistant Administrator for Air and 

Radiation, to Regional Office Air Division Directors, “Revised Policy to Address 

Reconsideration of Interpollutant Trading Provisions for Fine Particles (PM2.5), issued on July 

21, 2011. The memo indicated that, “First, upon re-examination of the original data, we believe 

that the original preferred ratios are not sufficiently representative of conditions in all areas of 

the country..... Second, we have determined that the ratios defined in the 2008 preamble are 

generally not suitable for application to offsets that address violations of the 24-hour primary 

PM2.5 NAAQS.”
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because the preferred ratios set forth in the 2008 PM2.5 rule addressed those two 

precursors. The overall discussion and request for comments pertain to any PM2.5 

precursor, which would also include VOC and ammonia.

21. Planning requirements not suspended with a Clean Data Determination (CDD)

a. Reviewer recommends providing additional clarification why certain planning 

requirements are not suspended with a CDD.

Response: We have added the underlined text below to page 413 to clarify why 

certain requirements are not suspended with a CDD. We have also added a 

footnote referencing the PM2.5 clean data policy issued in 2004.

“1. What is a clean data determination?

The EPA’s interpretation of the CAA applies when the agency, after 

notice and comment rulemaking, issues a “clean data determination” (CDD), in 

which it determines that a specific nonattainment area has attained the relevant 

standard. For such areas, the EPA interprets the CAA as suspending the state 

requirements to submit to the EPA the planning elements of an attainment plan 

related to attaining the NAAQS for as long as the area continues to attain the 

standard.3 These planning elements generally include reasonable further progress 

(RFP) requirements, attainment demonstrations, RACM/RACT, nonattainment 

area contingency measures, and other state planning requirements related to the 

attainment of the NAAQS. (Add footnote here: See December 14, 2004 

memorandum from Steven D. Page, Director, EPA Office of Air Quality Planning 

and Standards, entitled “Clean Data Policy for the Fine Particle National Ambient 

Air Quality Standards.” Available at: 

http://www.epa.gov/airquality/urbanair/sipstatus/docs/pm25_clean_data_policy_1

4dec2004.pdf) The suspension of the obligation to submit applies regardless of 

when the plan submissions are due. The CDD does not suspend CAA EPA 

planning requirements that are independent of helping the area achieve 

attainment, such as the requirements to submit an emissions inventory and 

nonattainment new source review requirements. The emissions inventory is a 

basic compilation of information used to characterize the sources of emissions of 

the nonattainment area. Section 172(c)(3), the statutory provision requiring 

submission of an emissions inventory, is not tied to attainment of the NAAQS, 

unlike the attainment planning provisions which are suspended by a CDD. A base 

year inventory continues to be relevant to a nonattainment area that is attaining 

 

3

In the context of CDDs, the EPA distinguishes between attainment planning 

requirements of the CAA, which relate to the attainment demonstration for an area and related 

control measures for bringing an area into attainment for a given NAAQS as expeditiously as 

practicable, and other types of requirements, such as permitting requirements under the NNSR 

program, and any specific control requirements independent of those strictly needed to ensure 

timely attainment of a given NAAQS.
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the NAAQS and has obtained a CDD because, for example, the inventory is a 

necessary component to an approvable redesignation request. In addition, in the 

event the air quality in the area exceeds the standard in a subsequent year, the 

state would be obligated to submit an attainment demonstration and other 

planning elements for the area, and a base year inventory would need to be 

available immediately in order for the state to submit an approvable attainment 

plan expeditiously. Similarly, the new source review requirement is not suspended 

because section 172(c)(5) is not tied to attainment of the NAAQS, andan area 

with a CDD is still designated nonattainment. NNSR permitting is required in 

each nonattainment area until the area is redesignated to attainment.”

22. Guidance for stationary source monitoring. (458)

a. Reviewer recommends modifying this section as it does not appear to be related 

to the rest of the rulemaking. This appears to be an information collection request 

that is related to a future potential guidance update that is not tied to this specific 

rulemaking effort.

Response: While we agree that the discussion is not directly associated with any 

particular requirement or information collection mandate of this rule, the EPA 

prefers to leave the discussion in to further its implementation efforts in 

partnership with states. Just as a woodsmoke reduction plan (mentioned in the 

preceding section K) can provide enforceable measures that reduce PM2.5 

emissions, so can improved stationary source emissions monitoring. Moreover, to 

the extent that we receive the requested data, our sharing of current, state-of-theart best practices to reduce PM2.5 emissions through improved emissions 

monitoring will help enable state agencies to develop source- or area-specific, 

cost-effective strategies for their SIPs.

23. EO 12866 and EO 13563. (486)

a. Reviewer recommends clarifying the statement that EPA submitted the action to 

the Office of Management and Budget (OMB) for review in 2011.

Response: We have revised the text here to be consistent with the latest action 

development process (ADP) templates, and eliminated the parenthetical “(76 FR 

3821, January 21, 2011).” 

Under Executive Order 12866 (58 FR 51735, October 4, 1993), this action 

is a "significant regulatory action” because it raises novel policy issues. 

Accordingly, the EPA submitted this action to OMB for review under Executive 

Orders 12866 and 13563 (76 FR 3821, January 21, 2011) and any changes made 

in response to OMB recommendations have been documented in the docket for 

this action.

This action is a significant regulatory action that was submitted to the Office of 

Management and Budget (OMB) for review because it raises novel policy issues. 
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Any changes made in response to OMB recommendations have been documented 

in the docket.

b. Reviewer recommends providing benefits and costs for this proposed rule within 

a regulatory impact analysis even if those benefits and costs are at the state level.

Response: A Regulatory Impact Assessment (RIA) was developed for the 2012 

PM2.5 NAAQS. As has traditionally been done for NAAQS rulemakings, the 

EPA conducted this RIA to provide the public with illustrative estimates of the 

potential costs and health and welfare benefits of attaining the revised annual 

standard. This document is available on the PM2.5 NAAQS website at: 

http://www.epa.gov/ttn/ecas/regdata/RIAs/finalria.pdf. 

EPA commonly provides a regulatory impact analysis for NAAQS revisions, but 

not for implementation rules.

24. Paperwork Reduction Act.

a. (486) Reviewer recommends clarifying why states without any nonattainment 

area would not be required to submit any information to the EPA for this rule.

Response: To address this comment, we have added a sentence indicating that 

only states with nonattainment areas would be required to submit SIPs under this 

rule. We have also revised the text to be consistent with the latest PRA template, 

and made a few clarifying edits.

“The information collection activities in this proposed rule have been 

submitted for approval to the Office of Management and Budget (OMB) under the 

PRA. The Information Collection Request (ICR) document prepared by the EPA 

has been assigned the EPA ICR number 2258.03, OMB Control No. 2060-0611.

You can find a copy of the ICR in the docket for this rule, and it is briefly 

summarized here.

The EPA is proposing this PM2.5 NAAQS SIP Requirements Rule to 

describe the CAA requirements that must be met by states with nonattainment 

areas required to develop SIPs for attaining and maintaining the NAAQS. The 

intended effect of the SIP Requirements Rule is to provide certainty to states 

regarding their planning obligations such that states may begin SIP development. 

Only states with nonattainment areas are required to submit SIPs under this rule.”

b. (487) Reviewer recommends providing additional basis for the estimated labor 

hours required and the estimated labor costs.

Response: Additional information about the estimated labor hours and estimated labor costs can 

be found in the supporting statement of the Information Collection Request (ICR) document 
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prepared by the EPA for this rulemaking. The ICR has been assigned the EPA ICR number

2258.03, OMB Control No. 2060-0611, and it will be available in the docket for this 

rulemaking.”

Specific Comments

1. Page 22.

a. Commenter recommends revising the statement “For example, PM2.5

concentrations are highest in the West and Southeast.” However, Table 2 shows 

that concentrations are highest in the West and Central.

Response: See response for item 2 below.

2. Page 23.

a. Commenter recommends deleting Table 2 as the regional information comes from 

1 to 34 stations within a region and may lead to conclusions that are incorrect. 

Because of so few stations the regional values are not statistically reliable and 

may not be representative of the region.

Response: We think that there is still benefit in including information in the 

preamble about PM2.5 composition for different regions of the country. For this 

reason, instead of deleting table 2, we have instead modified it to include

significantly more data, and better representation of the range of values in each 

region. With this additional data, we believe there will be less chance for the 

reader to draw incorrect conclusions. The table now contains data from all of the 

PM2.5 speciation sites in the Chemical Speciation Network. In addition, the 

information has been expanded to include the minimum and maximum 

concentrations for sites within in each region (in addition to the mean 

concentration for all sites in each region). This additional information provides a 

more complete assessment of the full range of observed PM2.5 and species 

concentrations within the monitoring network.

Table 2 and the introductory text now appear on page 23-25 as follows: 

“4. Fine Particulate Composition By Location

Table 2 shows regional 3-year mean concentrations (2009-2011) of PM2.5 and its main 

components at sites in the Chemical Speciation Network (CSN).

4

In addition to the mean values 

for all sites in each region, the table includes the minimum and maximum observed PM2.5 and 

species concentrations for sites within each region. These data illustrate broad observed spatial 

 

4 The organic matter (OM) values in Table 2 were calculated by multiplying the measured 

organic carbon (OC) concentrations by 1.6 (Turpin and Lim (2001), Aerosol Science and 

Technology, 35, 602-610). PM2.5 concentrations come from measurements of the Federal 

Reference/Equivalance Methods (FRM/FEM) rather than from the CSN PM2.5 measurement.
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patterns across the U.S. in PM2.5 concentrations and its composition. For example, PM2.5

concentrations are highest on average in the Central and West regions. Sulfate mass comprises a 

larger fraction of PM2.5 than nitrate mass in the northeastern U.S., whereas nitrate has a greater 

contribution than that of sulfate in the West. OM is the dominant component in all regions except 

the central U.S., with the highest concentrations of OM on average found in the West, Northwest 

and Southeast. On a percentage basis, the concentrations of EC and crustal material are relatively 

low throughout all regions of the U.S. compared to the other major PM components. 

The composition of PM2.5 also varies between urban and rural areas. This is reflective of 

the distribution of urban and regional emission sources, atmospheric reactions and transport of 

fine particles. More details about the spatial distribution and origins of PM2.5 components can be 

found in the docket for this proposal.

5

Table 2. PM2.5 Chemical Composition Data at 2009-2011 Nonattainment Sites

Source: EPA Speciation Trends Network

Region Statistic Concentration (μg/m3)

SO2

−4 NO−3 OM EC CrM PM2.5

Central Min (μg/m3) 1.46 0.3 2.73 0.31 0.01 8.92

Mean (μg/m3) 2.69 1.49 3.57 0.68 0.26 11.63

Max (μg/m3) 4.19 3.34 4.81 1.1 1.0 13.51

N 61 61 50 50 61 42

East North Central Min (μg/m3) 0.83 0.38 1.97 0.19 0.01 6.03

Mean (μg/m3) 1.68 1.8 2.84 0.48 0.19 9.86

Max (μg/m3) 2.51 3.57 3.69 0.79 0.61 11.87

N 29 28 20 20 28 23

North East Min (μg/m3) 0.58 0.12 1.74 0.14 0 4.42

Mean (μg/m3) 2.06 0.97 3.14 0.69 0.17 9.33

Max (μg/m3) 5.12 2.26 5.05 1.69 0.52 15.05

N 59 59 39 39 59 46

North West Min (μg/m3) 0.24 0.05 2.91 0.42 0.01 6.06

Mean (μg/m3) 0.54 0.4 5.02 0.81 0.15 8.33

Max (μg/m3) 1.09 1.79 8.44 1.25 0.53 10.96

N 33 33 13 13 33 14

South Min (μg/m3) 0.88 0.18 1.36 0.12 0.02 5.22

Mean (μg/m3) 2.06 0.8 3.32 0.57 0.5 10.05

Max (μg/m3) 3.08 1.67 5.1 1.48 2.38 14.27

N 36 27 23 23 36 23

South East Min (μg/m3) 1.6 0.2 1.75 0.37 0.01 6.76

Mean (μg/m3) 2.39 0.53 4.12 0.63 0.26 10.77

Max (μg/m3) 4.33 1.51 5.71 1.2 0.85 13.38

N 44 43 30 30 43 29

South West Min (μg/m3) 0.34 0.07 2.34 0.46 0.02 5.3

 

5 Reff and Rao, Memo to the docket, 2013.
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Mean (μg/m3) 0.63 0.49 3.01 0.7 0.5 7.93

Max (μg/m3) 1.13 2.65 4.39 1.04 1.96 9.73

N 46 46 11 11 46 12

West Min (μg/m3) 0.33 0.08 1.79 0.52 0.01 6.84

Mean (μg/m3) 0.9 1.4 5.22 0.85 0.32 11.49

Max (μg/m3) 2.08 5.14 10.27 1.56 1.05 16.57

N 44 44 20 20 44 21

West North Central Min (μg/m3) 0.29 0.06 1.22 0.09 0 3.23

Mean (μg/m3) 0.67 0.48 3.16 0.44 0.22 7.25

Max (μg/m3) 1.79 2.02 8.28 1.21 0.53 13.72

N 30 30 7 7 30 10

3. Page 39.

a. Commenter recommends providing additional information for determining that 

reducing regional SO2 and local sources of carbon in the East and local sources of 

nitrate and carbon in the West will be most effective in reducing PM2.5

concentrations. The additional information could be used by states to alleviate 

burden in relation to precursor demonstrations and attainment planning.

Response: The general statements in the draft preamble noted above were based on a 

basic evaluation of PM2.5 composition data from different regions of the country. 

These data are already publicly available. However, because the general observations 

in the text may be misinterpreted, we recommend that we delete the following 

sentences from page 41-42:

“For instance, in the East, regional pollution contributes to more than half of 

total PM2.5 concentrations. Rural background PM2.5 concentrations are high in the 

East and are somewhat uniform over large geographic areas. These regional 

concentrations come from emission sources such as power plants, natural sources and 

urban pollution and can be transported hundreds of miles. They also reflect to some 

extent the denser clustering of urban areas in the East as compared to the West.

In the West, much of the measured PM2.5 concentrations tend to be locally derived. These 

concentrations come from emission sources such as wood combustion and mobile sources. In 

general, these data indicate that reducing regional SO2 and local sources of carbon in the East, 

and local sources of nitrate and carbon in the West will be most effective in reducing PM2.5

concentrations.

This proposal takes into account the variability in the nature and sources of PM2.5 in 

different nonattainment areas and the need that states have to be able to develop control 

strategies for direct PM2.5 and PM2.5 precursors that reflect the variable nature of their sources.”

4. Page 107.

a. Commenter recommends clarifying how attainment demonstration modeling 

emissions inventories may not be consistent with the emissions inventories 
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developed for the nonattainment area and how the nonattainment area emissions 

inventories are used for the attainment demonstration modeling.

Response: We have revised the text in this section to address this comment. The following text 

will replace the relevant preamble section around page 109:

“7. How do emission inventories support modeling for attainment demonstrations?

This section attempts to clarify the difference between the inventories required to be a 

part of a state’s Moderate area attainment plan submission (as described earlier) and other 

modeling inventories that are also relevant for attainment planning. While the EPA is not 

proposing additional modeling inventory requirements in this rule (i.e., for which a state must 

submit an emissions inventory to the EPA), to meet the attainment demonstration requirements 

of CAA sections 189(a)(1) and 189(b)(1), states will need to submit an attainment demonstration 

(which includes air quality modeling) to show how the area will either attain the NAAQS by the 

applicable attainment date or that the area cannot attain by the attainment date. The modeled 

attainment demonstration requirements for Moderate areas are described fully in Section IV.E of 

this preamble.

As part of this demonstration, the EPA presumes that states will need to prepare 

attainment demonstration modeling inventories for both a modeled base year and projected 

attainment year. Respectively, these are called the base year (baseline) inventory for modeling

and the attainment projected inventory for modeling. These inventories contain emissions for all 

regions (i.e., not just the nonattainment area) within the modeling domain being used for the 

attainment plan modeling demonstration, which typically includes counties and states outside of 

the nonattainment area. They include detailed spatial and temporal elements needed to support 

air quality modeling. States should follow the requirements laid out in Section IV.E of this 

preamble and the procedures described in the SIP Emissions Inventory Guidance and the Air 

Quality Modeling Guidance to meet the minimum requirements for documentation and 

emissions summaries supporting modeling demonstrations.

The base year inventory and projected attainment year inventory include emissions from 

only within the nonattainment area. The EPA expects that modeling inventories will be 

consistent with those nonattainment area inventories; however, some exceptions may exist. 

Where possible, the nonattainment area base year and projected attainment year inventories can 

be a sum (for annual data) or average (for PM2.5 season-day data) of day-specific or hourspecific data used for modeling. In some cases, however, this approach may not be sufficient for 

modeling purposes. For example, greater spatial and temporal detail are needed for on-road 

mobile modeling inventories as compared to the base year inventory for the nonattainment area. 

For the nonattainment area base year inventory, one goal is to allow for the repeatability of the 

approach in order to create average, seasonal, or annual inventories for use in rule requirements, 

such as reasonable further progress or conformity demonstrations. That goal is not necessarily 

compatible with the modeling need for greater spatial and temporal detail. In cases where some 

differences are unavoidable, air agencies should attempt to promote consistency where feasible.

b. Commenter recommends providing additional information on how emissions of 

PM2.5 and PM2.5 precursors outside of the nonattainment area may be affected 

(i.e., regulated or controlled) as a result of the modeling demonstrations.
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Response: The modeling demonstration typically will employ a modeling 

domain that extends beyond the boundaries of the nonattainment area, and the 

state commonly will conduct modeling runs to assess the effectiveness of certain 

emission reduction measures on sources throughout the entire modeling domain. 

The state has jurisdiction over emissions sources throughout the entire state, and it 

has the ability to adopt regulations that apply to sources across the whole state in 

order to help address multiple air quality related issues at the same time. For 

example, some states have adopted statewide regulations to reduce SO2, NOx, 

direct PM2.5, and mercury from power plants to efficiently address multiple air 

pollution problems (i.e. PM2.5, ozone, mercury deposition) and to provide a level 

regulatory “playing field” for a particular industry or sector. This implementation 

rule provides flexibility to the state to determine the most appropriate mix of 

control measures needed to bring an area into attainment with the NAAQS “as 

expeditiously as practicable.” That said, if potential control measures are available 

in the state on sources located either within or outside the nonattainment area, and 

this collection of control measures would enable the area to attain the standard at 

least one year sooner, then the state would be obligated to adopt provisions to 

require such emission reductions. 

5. Page 111.

a. Reviewer recommends modifying “States can alternatively develop superior statespecific nonroad emissions estimates . . . .” to state “States can alternatively 

develop technologically equivalent or superior state-specific nonroad emissions 

estimates . . . .”

Response: We have added the recommended text to the sentence noted above on

page 114.

6. Page 134.

a. Reviewer recommends removing brackets from “in the area” quotation with 

respect to the “nonattainment area” and providing a footnote of the court decision 

and how it applies.

Response: To address this comment, we have revised the sentence on page 138 as 

follows:

“In that proposal, the EPA explained that given the explicit wording of section 

172(c)(1) that sources “in the [nonattainment] area” (i.e., in the nonattainment 

area) must at a minimum adopt RACT controls for that area, the agency believes 

that it is no longer appropriate to presume that this requirement is satisfied merely 

based upon the participation of a source in a regional cap-and-trade program.

Footnote 95 provides a reference to the court decision and how it applies.
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7. Page 137.

a. Reviewer recommends providing additional discussion on the economic 

feasibility determination recommended in the 2007 PM2.5 rule.

Response: See response to comment 8a under “General Comments.”

8. Page 139.

a. Reviewer recommends adding to the list: 8. Impact on jobs and 9. Cumulative 

impacts to the source not considered above (e.g., delays in maintenance or other 

potential safety-related actions).

Response: See response to comment 8a above.

9. Page 327.

a. Reviewer recommends clarifying that “in writing” includes electronic submittals 

within Step 5.

Response: We have deleted the two references in this document to submitting 

information to EPA “in writing” (both of which appear in this section on 

submitting Serious area attainment date extension requests on page 332) because 

states already commonly send different types of submittals to EPA via electronic 

means. We have removed the phrase “in writing” to avoid any confusion.

10. Rule Language

a. (507) §51.100 – reasonable further progress is defined as “annual incremental 

reductions in emissions . . . .” Reviewer recommends clarifying whether periodic 

step-down functions are included within RFP.

Response: This type of clarification does not need to be included in rule 

language on RFP, as the “step-wise function” and the “generally linear reduction” 

approaches are both already discussed in the preamble around page 190.

b. §51.1006(a) – reviewer recommends removing or revising the second sentence 

starting with “The technical analysis could include . . . .” as this language is more 

appropriate for guidance documents or discussion within the preamble.

Response: We have removed the sentence in question on page 528.

c. (520) §51.1007(d) – reviewer recommends removing or revising this subpart as 

this language is more appropriate for guidance documents or discussion within the 

preamble.

Response: We have removed the sentence in question on page 529.
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d. §51.1008 – reviewer recommends clarifying why there are timing requirements 

within §51.1008(b)(3) for Serious nonattainment areas and not for Moderate 

nonattainment areas within §51.1008(a).

Response: We have removed the timing requirements under paragraph 

51.1008(a) and revised the proposed regulations at 51.1003 to clarify the timing 

requirements for different emissions inventory submissions for different types of 

PM2.5 nonattainment areas.

Typographical Comments

1. Page 40.

a. Commenter recommends ensuring that: 

i. Tier 2 Light-Duty vehicle standards be cited instead of Tier 3

ii. Green House Gas standards for Light-Duty and Heavy-Duty vehicles do 

not need to be cited.

Response: We have revised the list on page 43 of national regulations and 

standards that will help PM2.5 nonattainment areas in reaching attainment. The 

Tier 3 vehicle and fuel standards were finalized in 2014 and emission reductions 

should begin in 2017, thus we feel it is appropriate to include this rule on the list. 

The “Green House Gas Standards” referred to by the reviewer are not referenced. 

The revised text reads as follows:

“The national rules that will help states meet their attainment dates include, but 

are not limited to: the Tier 2 Light-Duty Vehicle Rule; the Tier 3 Tailpipe and 

Evaporative Emission and Vehicle Fuel Standards; the Heavy-Duty Engine and 

Vehicle Standards and Highway Diesel Fuel Sulfur Control Requirements; the 

Clean Air Nonroad Diesel Rule; the Regional Haze Regulations and Guidelines 

for Best Available Retrofit Technology Determinations; the NOx Emission 

Standard for New Commercial ....”

b. Commenter recommends clarifying if the Heavy Duty rule is the Tier 2 Heavy 

Duty Diesel rules.

Response: We have referred to these rules as “the Heavy-Duty Engine and 

Vehicle Standards and Highway Diesel Fuel Sulfur Control Requirements,” as 

they are referred to in our fact sheets. 

c. Commenter recommends updating footnote 47.
EPA Response to Summary of Interagency Working Comments on Draft 

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Response: The purpose of the reference to the 1991 NAPAP report in footnote 

47 is to show that evidence of long-range transport of particulate matter has been 

documented and well-understood for many years. For this reason, we are keeping 

footnote 47 as is.

2. Page 242.

a. Add additional “)” after “section 172(c)(6)”.

Response: This change has been made.

3. Page 518.

a. Recommend revising §51.1005(c) as there appears to be words missing.

Response: We have revised this paragraph on page 527 to provide more clarity.

“(c) Serious nonattainment areas subject to CAA section 189(d) for failing to 

attain by the applicable Serious area attainment date. If A state with a Serious area 

that failsed to attain a particular PM2.5 NAAQS by the applicable Serious area 

attainment date, the area is and is therefore then subject to the requirements of 

section 189(d) of the Act, and, for this reason, the state is prohibited from 

requesting an extension of the applicable Serious area attainment date for such 

area.”

4. Page 536.

a. Part of the first sentence for §51.1011(a) and (b) is underlined and should be 

removed.

Response: Change has been made.

5. Reviewer recommends defining the following terms and ensuring that all acronyms used 

within the preamble are also provided within the preamble glossary of terms and 

acronyms:

a. FRM 

b. FEM

c. NESHAPs

Response: We have revised the glossary to address these terms.

6. Reviewer recommends revising all cases where the term “whether or not” is used to state 

“whether”. For example, on page 398, the sentence, “The requirements differ depending 

on whether or not the nonattainment area is considered a metropolitan area.” (emphasis 

added). Should be revised to state, “The requirements differ depending on whether the 

nonattainment area is considered a metropolitan area.”
EPA Response to Summary of Interagency Working Comments on Draft 

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Policy Review. Final: 1/23/2015

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Response: This change has been made on page 405; and it was only case of 

“whether or not” that appeared in the document.