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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

Note: This second set of responses to interagency comments responds to follow-up comments on 

only selected issues that we addressed in the first set of responses. These follow-up comments 

were received and discussed in conference calls during the week of February 2-6, 2015. Also, the 

last section addresses five new comments that were received on 2/10/2015.

1. Wildfire and wildland fire.

a. Initial Comment: 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.

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

emissions.”

b. New Comment: A reviewer provided the following edits in bold to this paragraph: 

“Wildfire emissions are a component of background PM2.5 and 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, behavior, and effects of catastrophic wildfires which may help 

manage the contribution of wildfires to background PM2.5 levels and periodic peak PM2.5 

events. 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 prescribed wildland fire use to reduce the impact of wildfire related 

emissions on PM2.5.

EPA Response: EPA has included the above edits.

New Comment: A reviewer also suggested including the following paragraph to the RACM 

section of the rule. 

“If wildfire impacts are significant, contributing to exceedances of the standard, states should 

consider Reasonably Achievable Control Measures (RACM) for this source. Fires play an 

important ecological role across the globe, benefiting those plant and animal species that depend 

upon natural fires for propagation, habitat restoration, and reproduction. Fires are one tool that 

can be used to reduce fuel load, unnatural understory, and tree density, helping to reduce the risk 

of catastrophic wildfires. Some wildfires and the use of prescribed fire can influence the 

occurrence of catastrophic wildfires which may reduce the probability of fire-induced smoke 

impacts and subsequent health effects. RACM for catastrophic wildfire may include addressing 

the wildland fuels through fuels management, including the use of prescribed fire and allowing 

some wildfire to occur naturally in systems that are ecologically fire dependent. Where 

appropriate, states, land managers, and landowners may consider developing plans to ensure that 

fuel accumulations are addressed and fuels management efforts, including prescribed fire, are not 

delayed. RACM for prescribed fires should also be considered. Information is available from 

the DOI and the USDA Forrest Service on smoke management programs and basic smoke 

management practices and may be considered when determining RACM for prescribed 

fires. RACM must be determined for each area on a case-by-case basis.”
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EPA Response: In a conference call on 2/5/2015, it was agreed that EPA would develop a 

modified version of this paragraph and would include a request for comment on these issues. Our 

suggested language to be inserted in the RACM section on page 128 is as follows: 

“It was noted in Section II of this preamble that national PM2.5 emissions from wildfire 

are substantial. In some areas, wildfire impacts can be significant and contribute to exceedances 

of the PM2.5 standard and adverse health effects. Fires also play an important ecological role 

across the globe, benefiting those plant and animal species that depend upon natural fires for 

propagation, habitat restoration, and reproduction. Fires are one tool that can be used to reduce 

fuel load, unnatural understory, and tree density, helping to reduce the risk of catastrophic 

wildfires. Some wildfires and the use of prescribed fire can influence the occurrence of 

catastrophic wildfires which may reduce the probability of fire-induced smoke impacts and 

subsequent health effects.

In light of these wide-ranging effects of fire and the uniqueness of this category of 

emissions, the EPA requests comment on the concept of RACM to reduce the impacts of 

emissions from catastrophic wildfire and prescribed fire. Wildland fuels can be reduced through 

fuels management, including the use of prescribed fire and allowing some wildfire to occur 

naturally in systems that are ecologically fire dependent. Where appropriate, states, land 

managers, and landowners may consider developing plans to ensure that fuel accumulations are 

addressed and fuels management efforts, including prescribed fire, are not delayed. RACM for 

managing emissions from prescribed fires should also be considered by air agencies. Information 

is available from the DOI and the USDA Forest Service on smoke management programs and 

basic smoke management practices. The EPA requests comments and ideas about the concept of 

RACM for wildfire and prescribed fire, and requests input on practical considerations associated 

with how such measures can be characterized in emissions inventories and attainment 

demonstrations, and made federally enforceable for adoption in a nonattainment area SIP.“

8. Economic feasibility determination.

Initial Comment: A reviewer has recommended that two additional factors - 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) - be added to the list of economic feasibility factors 

excerpted from page 142 of the preamble below: 

“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
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5. Company profits

6. Employment costs

7. Other costs (e.g., for RACM implemented by public sector entities).

The EPA seeks comment on the factors described above for states to consider when 

determining whether a control technology or measure is economically feasible.”

EPA Response: 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. 

New Comment: Commenters suggested adding a reference in the text to the relevant 

guidance mentioned above.

EPA Response: EPA has included a footnote citing the 1992 General Preamble 

appendices in the preamble. The footnote reads: 

“These long-standing factors were established in EPA guidance in 1992 and are 

applicable to implementation programs for all NAAQS pollutants. See the appendices to 

the General Preamble, 57 FR 18070 (April 28, 1992).”

9. Attainment demonstration.

A. Initial Comment: Reviewer recommends providing a discussion of 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: On a conference call on 2/2/2015, EPA agreed to add a discussion of the potential 

benefits and costs of the four options for unmonitored area analyses. Our suggested insert for 

page 182 is below:

“The four options presented above would lead to a range of potential analysis costs, 

control costs, and health benefits. Option 1 would be expected to be the least costly option, in 

term of both analysis costs for implementing air agencies, and in terms of potential control costs 

for the regulated community. Option 2 would be expected to be the most resource intensive 

option to implement, and if potential violations were identified in unmonitored areas, this option 

could also lead to additional costs for regulated entities to reduce emissions. However, any 

additional emission reductions (in comparison to option 1) that would result from 

implementation of this approach would lead to additional health benefits in the area. Option 3 is 
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similar to option 2, except that if a potential violation is indicated in an unmonitored area, there 

would not be a regulatory requirement for the air agency to identify enforceable controls to 

eliminate the potential violation. For example, the air agency could instead elect to site a new 

monitor to further characterize air quality in the area. The analysis costs associated with option 3 

would be the same as for option 2, but the potential for additional control costs and health 

benefits could vary widely, depending on the agency’s assessment and choice regarding further 

action. Option 4 most closely describes the current policy for the PM2.5 implementation 

program. Currently, EPA recommends that air agencies conduct an unmonitored area analysis, 

but there is no regulatory requirement for the air agency to either perform an unmonitored area 

analysis or to impose control requirements if the analysis indicates potential violations. Thus, 

under option 4, if an unmonitored area analysis is performed, the analysis costs associated with 

this option would be the same as for option 2. Similar to option 3, the potential for additional 

control costs and health benefits could vary widely, depending on the agency’s assessment. 

Under option 4, if it is determined by EPA and the air agency to be unnecessary to perform an 

unmonitored area analysis, there would be no additional analysis or control costs or health 

benefits beyond the monitor-only approach of option 1.”

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

a. Comment: 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: On 1/23/2015, we indicated we would 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. Our suggested revision to this section reads as follows:

“4. Geographic coverage of emission sources for RFP

EPA is proposing that the RFP demonstration to be included with a state’s PM2.5 

nonattainment area plan must include emissions only for sources located in the nonattainment 

area, and not from an area larger than the nonattainment area. This policy approach differs from 

the remanded 2007 PM2.5 implementation rule. This section describes the evolution of policy 

on a similar RFP issue in the ozone NAAQS implementation program, and it discusses the 

reasoning behind this revised approach for PM2.5.

In the preamble to the remanded 2007 PM2.5 Implementation Rule (which provided 

guidance for states on implementing the 1997 PM2.5 NAAQS), the EPA allowed states to 

incorporate reductions of NOx and SO2 emissions up to 200 km from outside the nonattainment 

area (and potentially for reductions of VOC or ammonia) into their RFP plan when certain 

conditions were met. This policy was included in the 2007 PM2.5 Implementation Rule in part to 

be consistent with a similar RFP policy for NOx and VOC that was included in the November 
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2005 Phase 2 ozone NAAQS implementation rule which provided guidance for states on 

implementing the 1997 ozone NAAQS.

1

Note that under the policy in the 2007 PM2.5 Implementation Rule, if a state intended to 

include emission reductions from outside the nonattainment area in the RFP plan, the state would 

need to take on the additional work associated with developing 1) an expanded baseline 

emissions inventory for the entire geographic area (i.e., the nonattainment area plus the 

additional area outside the nonattainment area) that characterizes emissions for all stationary, 

area, and mobile sources (rather than for just a select few stationary sources) in the overall area; 

and 2) a projected attainment year inventory for this expanded area outside the boundaries of the 

designated nonattainment area. By requiring inclusion of all types of sources in these “expanded 

area” emission inventories, the EPA intended for this approach to reflect the projected net 

emissions reductions in this area (the difference between the “expanded area” base year 

inventory and the projected attainment year inventory). However, it should be noted that for a 

state to develop these more extensive inventories, it would likely involve a substantial amount of 

additional time and resources. In addition, the state would need to provide information 

supporting their decision regarding how far outside the nonattainment area the RFP inventory 

should extend. While this “outside the nonattainment area” RFP approach was theoretically 

available to states in developing their PM2.5 attainment plans that were due in 2008, there were 

no states that elected to follow this approach. 

Both the 2005 Phase 2 ozone implementation rule and the 2007 PM2.5 implementation 

rule were challenged on several issues. With regard to the Phase 2 ozone implementation rule, 

the EPA granted a petition for reconsideration and ultimately issued a final notice of 

reconsideration in June 2007. In November 2008, the U.S. Court of Appeals for the D.C. Circuit 

heard oral argument concerning multiple petitions for judicial review of the Phase 2 ozone rule 

and the notice of reconsideration. One of the issues in this case involved whether compliance by 

electric generating units (EGUs) with a regional emissions trading program could be considered 

to meet the RACT requirement for those sources located in a nonattainment area. In its July 2009 

decision, the Court emphasized that: ‘‘the RACT requirement calls for reductions in emissions 

from sources in the area; reductions from sources outside the nonattainment area do not satisfy

the requirement . . . Accordingly, participation in the NOx SIP call would constitute RACT only 

if participation entailed at least RACT-level reductions in emissions from sources within the 

nonattainment area.’’ 

In light of this court decision, the EPA has determined that the best reading of the statute 

would be to interpret the term “sources in the area” in the same manner where it appears in 

different nonattainment provisions for ozone. The term appears in section 182 (requirements for 

ozone nonattainment areas) with regard to RFP as well as RACT. The NRDC decision found that 

section 182(b)(2) requires that a SIP must provide for implementation of RACT (under section 

172(c)) for emissions sources “in the area,” meaning in the nonattainment area. In a consistent 

manner, EPA believes that when section 182(b)(1)(A)-(B) defines baseline emissions for RFP as 

 

1 See Phase 2 Ozone Implementation rule, 70 FR 71612, November 29, 2005.
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“the total amount of actual VOC or NOx emissions from all anthropogenic sources in the area,” 

this also means sources “in the nonattainment area.”

With regard to the 2007 PM2.5 implementation rule, the EPA received a petition for 

reconsideration in June 2007 that raised objections on several issues. One such issue dealt with 

the EPA’s interpretation of the statutory RFP requirements to allow a state to take “credit” for 

emissions reductions from outside the nonattainment area when addressing RFP in its attainment 

plan.2 The EPA granted the petition for reconsideration on this issue in 2010, after the D.C. 

Circuit issued its decision on the Phase 2 Ozone Implementation Rule.3, 4

Specifically, the EPA believes that the D.C. Circuit’s interpretation of the phrase 

“sources in the area” applies to RACT and RFP requirements for both the ozone NAAQS and the 

PM2.5 NAAQS. In particular, for PM2.5, the statutory language at section 171(1) defines RFP in 

terms of “reductions in emissions” required in an attainment plan, which the EPA interprets as 

being directly linked to the baseline emissions inventory for sources located in a PM2.5

nonattainment area. The baseline emissions inventory is the foundation for the attainment plan. 

The emissions inventory requirement of section 172(c)(3) explicitly requires that the attainment 

plan inventory include all sources of the relevant pollutants “in such area,” which is a clear 

reference to the designated nonattainment area. Given that the baseline inventory must reflect the 

emissions “in such area,” and that this inventory provides the starting point for a state’s RFP 

analysis, in which the state must calculate generally linear progress in emissions reductions that 

will lead to attainment of the NAAQS in the area, the EPA believes it is appropriate that a state 

should focus on sources located within the nonattainment area when conducting its analysis to 

determine the annual emissions reductions necessary for demonstrating RFP.

EPA believes that the most appropriate approach with regard to the geographic area 

required to be covered for demonstrating RFP in a PM2.5 attainment plan also should be limited 

to the nonattainment area for two other reasons. First, EPA believes that it makes policy sense 

for the PM2.5 implementation rule approach to be consistent with the approach in the ozone 

implementation rule. In the past, a number of areas have been designated as nonattainment for 

both standards, and the nonattainment area boundaries often are the same. For such areas, a 

common policy approach for the geographic area covered by the RFP plan will be more efficient 

to implement and would be expected to be less burdensome for the air agency than if the 

geographic areas covered by RFP plans for the two pollutants differed. 

 

2This same petition raised concerns regarding the criteria used to determine the economic 

feasibility of controls being considered for RACT for the 1997 PM2.5 NAAQS. See “Petition for 

Reconsideration,” filed by Paul Cort, Earthjustice, on behalf of the American Lung Association, 

Medical Advocates for Healthy Air, Natural Resources Defense Council, and the Sierra Club 

(June 25, 2007). A copy of the petition is in the docket for this action.

3Letter dated May 13, 2010, from Gina McCarthy to David S. Baron and Paul Cort, Earthjustice. 

A copy of the letter is located in the docket for this action.

4

See NRDC v. EPA, 571 F.3d 1245 (D.C. Cir. 2009).
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Second, a policy allowing the geographic area of the RFP plan to be larger than the 

nonattainment area would conflict with a key provision of subpart 4 which requires annual 

incremental reductions in emissions from sources within the nonattainment area. Under subpart 

4, an area that fails to attain the standard by the Serious area attainment date is then subject to the 

provisions of section 189(d). Section 189(d) specifies that the state must submit a plan revision 

within 12 months which provides for “an annual reduction in PM–10 or PM–10 precursor 

emissions within the area of not less than 5 percent of the amount of such emissions as reported 

in the most recent inventory prepared for such area” (emphasis added). The EPA does not 

believe the rule should include an RFP policy approach which would not be consistent with 

section 189(d).

After reconsideration of the approach to RFP that was opposed in the petition for 

reconsideration of the 2007 PM2.5 Implementation Rule, and in light of the D.C. Circuit decision 

on the Ozone Phase 2 Implementation Rule, the EPA believes the best reading of the statute is 

that the CAA does not allow for a state to include emissions reductions from sources outside a 

nonattainment area when developing the plan to meet the CAA section 172(c)(2) RFP 

requirements for a PM2.5 nonattainment area. The EPA seeks comment on this proposed 

approach.”

14. Emission inventory.

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

emissions estimating methodologies (EEM) for animal production operations under the 

National Air Emissions Monitory Study (NAEMS) when they become available.

Response on 1/23/2015: 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 
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every source category in this rulemaking notice, nor would we do so for a single source 

category.

New Comment: During a 2/5/2015 conference call with interagency representatives, it was 

decided that a few sentences should be added about ammonia emissions to the emission 

inventory section in the preamble. 

Response: EPA has added additional text on ammonia emissions in the section below. The 

recommended underlined text would appear around page 108. The overall section is included 

for context. 

“5. Why is the EPA requiring certain pollutants be included in the inventories?

The EPA is proposing that states must submit emissions inventories that include all 

emissions of direct PM2.5 and all emissions of all PM2.5 precursors: SO2, NOx, VOC and 

ammonia. Furthermore, the inventory must differentiate between the condensable and filterable 

portions of direct PM2.5 emissions. Section II.B of this proposal describes the background needed 

to understand the importance of including these precursors in emissions inventories for 

attainment plan purposes for the PM2.5 NAAQS. Emissions information about PM2.5 and its 

precursors is a necessary precondition to meeting other core attainment plan requirements, such 

as effective evaluation of control measures and adequate demonstration of projected future 

attainment of the NAAQS through modeling. The EPA notes that with respect to requiring states 

to include emissions of direct PM2.5 and PM2.5 precursors in emissions inventories, the agency is 

following the requirements it has established for the PM2.5 NAAQS in the past. Section 172(c)(3) 

explicitly requires states to submit a “comprehensive, accurate, and current inventory of actual 

emissions of the relevant pollutants” and the EPA concludes that in order to meet these basic 

statutory requirements for the PM2.5 NAAQS, states must address PM2.5 and all PM2.5 precursors 

in their emissions inventories. The EPA requires air agencies to use the best available 

methodologies for estimating emissions of direct PM2.5 and its precursors. It should be noted that 

for ammonia, in particular, updated emission estimating methodologies for animal feeding 

operations are under development using data collected during 2007-2009 from representative 

operations pursuant to the National Air Emissions Monitoring Study. The EPA is hopeful that 

such updated methodologies will help reduce uncertainties in current ammonia inventories and 

will improve the quality of future emissions inventories needed for implementing the PM2.5 

NAAQS.”

16. Quantitative milestones.

a. Initial Comment: 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: 
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“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.5

New Comment: On a 2/2/2015 conference call, reviewers suggested including additional 

clarification on this issue. 

EPA Response: We have now changed the underlined sentence to read: 

“Thus, using the example described above, the annual reduction requirement for the area 

would be 5 tons/day from a base year emissions level of 100 tons/day. The required level 

after year 1 would be 95 tons/day, after year 2 the level would be 90 tons/day, and so on. If 

the air agency reached a level of 81 tons/day by the end of year 3, then by the end of year 4 it 

would only need to reduce emissions by 1 ton/day to yield an emissions level of 80 

tons/day.”

20. Major source thresholds for PM2.5 precursors.

c. Initial Comment: 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.

Initial 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 

 

5

69 FR 30006 (May 26, 2004).
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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.6 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. 

New Comment: Commenter recommends further clarification of these issues. 

Response: EPA has revised this section (around page 392 and 394) to read: 

“Moreover, the EPA believes that a reasonable argument can be made that whatever 

threshold is set for PM2.5 emissions, the same level would be too low to be regarded as 

“major” for each precursor when considering the effects that such precursor sources 

could have on ambient PM2.5 concentrations. The EPA previously analyzed the 

relationship between emissions of SO2 and NOx and the formation of secondary PM2.5 in 

the ambient air expressly for purposes of determining an appropriate ratio for allowing 

interprecursor offsets for PM2.5. Those studies resulted in the EPA providing in the 2008 

PM2.5 NSR Rule “preferred” ratios for both SO2 and NOx, 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.7In brief, the preferred ratios were 

as follows: for NOx-to-primary PM2.5: 200 to 1 (NOx tons to PM2.5 tons) for areas in the 

eastern U.S, and 100 to 1 for areas in the western U.S.; and for SO2-to-primary PM2.5: 40 

to 1 (SO2 tons for PM2.5 tons). In each case, the ratio illustrates that it requires 

considerably more precursor emissions than direct PM2.5 emissions to result in a 

particular ambient concentration of PM2.5. It should be noted that at that time the EPA did 

not consider using the preferred ratios for the purpose of adjusting the major source 

thresholds or significant emissions rates for SO2 and NOx when regulating as PM2.5

precursors.”

 

6 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.”

7 The technical assessment, with details on data and modeling inputs, was fully described in a 

technical memo titled “Details on Technical Assessment to Develop Interpollutant Trading 

Ratios for PM2.5 Offsets,” which was placed in the docket to the 2008 final rule. See also 73 FR 

28339.
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...

“The EPA does not believe that a sufficient technical basis exists at this time to enable 

the agency to propose specific higher major source thresholds for any of the four PM2.5

precursors presumptively regulated in PM2.5 nonattainment areas.”

23. EO 12866 and EO 13563.

d. Initial Comment: 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.

Comment: Reviewer requests adding a reference to the RIA to this section.

Response: We have now added a footnote to this section, which reads: 

“Note that a regulatory impact analysis evaluating the costs and benefits 

associated with attaining the 2012 PM2.5 NAAQS was released at the time the 

NAAQS review was finalized. See “Regulatory Impact Analysis for the Final 

Revisions to the National Ambient Air Quality Standards for Particulate Matter.” 

U.S. Environmental Protection Agency, Office of Air Quality and Planning 

Standards, Health and Environmental Impacts Division, February 28, 2013. EPA452/R-12-005.”

Additional Comments Received on 2/10/2015

1. Comment: Reviewer recommends providing additional information on whether food 

security, the availability of an abundant and affordable food supply, and ecosystem 

impacts, in addition to technical and economic feasibility and adverse environmental or 

energy effects, in determining the “reasonableness” of mitigation/control options, 

especially in relation to ammonia. This relates to page 54, and the use of term “additional 

reasonable measures” to identify additional measures that are not included in RACM and 
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EPA’s response to comments that PM10 and ozone programs do not have this term as 

those programs already include specific requirements.

Response: Our response to this suggestion from the reviewer (to add additional factors 

for states to consider in determining technological and economic feasibility of potential 

control measures) is similar to the response we have provided on pages 3-4 above 

regarding suggested changes to the factors for economic feasibility. The set of factors to 

be considered by states in determining “reasonable” control measures is described in 

depth in pages 120-150 in section 2. Identification and selection of RACM and RACT and 

additional reasonable measures. These factors are taken from long-standing guidance 

(the 1992 General Preamble) that is applicable to implementation of more than just the 

PM NAAQS. 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 may or may not be able to afford control technology used on similar sources. 

For example, it appears that an issue such as food security could be addressed under 

economic factors in existing guidance dealing with product supply and product prices. As 

indicated before, we think that changing within this preamble the longstanding guidance 

that has applied to all NAAQS risks introducing confusion to states in their attainment 

planning processes for this NAAQS and for other NAAQS as well, with little potential 

gain in return. 

2. Comment: Reviewer recommends providing additional clarification on why PM10 

requirements for control measures guidance documents do not apply to PM2.5, as PM2.5 

is a subset of PM10 (one of the bases for the regulating PM2.5 under Subpart 4). If the 

previous statement is correct, should the requirements for PM2.5 be the same as PM10?

Response: Section 190 was included in the 1990 Clean Air Act Amendments, and it 

directed EPA to issue guidance on RACM and BACM for three important source 

categories – urban fugitive dust, residential wood combustion, and prescribed burning –

which were identified at that time as key contributors to high concentrations of PM10 

(which at the time was the only PM-related NAAQS in effect). EPA issued guidance on 

those topics at that time and has fulfilled this statutory requirement. Moreover, much has 

been learned in the scientific and air quality management communities in the past twenty 

years to inform the actions of air agencies as they develop control strategies to attain 

PM2.5 standards. We do not believe the control measure requirements for PM2.5 should 

be the same as for PM10. PM2.5 is a much more complex pollutant than PM10, and 

many new and/or more cost-effective emission reduction technologies and management 

techniques exist today that did not exist in the 1990’s. The Act does not require EPA to 

update the 1990 guidance for either PM-10 or PM-2.5, and EPA does not plan to do so at 

this time. However we will assist states in the development of their RACM and BACM 

plans.

3. Comment: Reviewer recommends providing additional discussion on ammonia as the 

primary sources of ammonia are currently identified in the EPA’s National Emissions 

Inventory to be “livestock raising” (54%) and “fertilizer application” 
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(27%). Specifically, given that ammonia emissions from these sources are primarily 

driven by biological activity and meteorology, which have generally less opportunity for 

human control than chemical or mechanical processes, how is this relative lack of ability 

for human control into control technologies for these sources incorporated within 

mitigation and control options? Can these limitations be included in a state’s 

determination of “reasonableness” or “feasibility”?

4. Comment: Reviewer recommends providing additional clarification as ammonia is a 

reactive nitrogen species with multiple environmental pathways, how is the potential for 

other nitrogen-related environmental impacts from reactive nitrogen due to potential 

ammonia controls evaluated? Is this an aspect that can be considered in a 

“reasonableness” determination as related to adverse environmental impacts? How are

ammonia air emission impacts weighed in relation to potential water quality or other 

environmental impacts?

Response to Comments 3 and 4: We understand that there are specific issues that arise 

when considering potential emission reduction strategies for ammonia. However, it can 

be argued that specific issues arise when considering control measures for many other 

categories of emissions as well. The preamble sections on RACT/RACM and 

BACT/BACM both include an extensive discussion of the general framework for air 

agencies to follow in considering a range of factors in determining economic and 

technological feasibility of control measures, in order to make judgments about what 

measures could be “reasonable” for a particular nonattainment area. For example, on 

page 135 of the draft preamble, it states:

“Furthermore, the EPA believes that reducing air emissions may not justify adversely 

affecting other resources, for example, by increasing pollution in bodies of water, creating 

additional solid waste disposal problems or creating excessive energy demands. An otherwise 

available control technology may not be reasonable if these other environmental impacts are 

sufficiently adverse and cannot reasonably be mitigated. The EPA proposes that a state may 

consider a control measure for direct PM2.5 or a PM2.5 precursor not reasonable if, 

considering the availability of mitigating adverse impacts of that control on pollution of other 

media, the control would not, in the state's reasoned judgment, provide a net benefit to public 

health and the environment. It should be noted that, in many past situations, states and 

owners of existing sources have adopted control technologies for direct PM2.5 and/or PM2.5

precursors with known energy penalties and some adverse effects on other media, based on 

the reasoned judgment that installation of such technology would result in a net benefit to 

public health and the environment. States should consider this before determining that a 

control technology is not reasonable because it may have other, negative environmental 

impacts that are, on balance, marginal.” 

State implementation plans will address ammonia and other precursor issues on a case-bycase basis, as supported by the state’s reasoned judgment. As indicated in our initial set of 

responses, we think the existing guidance on economic and technological feasibility of 

control measures has proven sufficiently broad and has provided adequate flexibility to states 
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to be able to present reasoning to demonstrate why certain facilities are not able to afford 

control technology used on similar sources. We think that changing within this preamble the 

longstanding guidance that has applied to all NAAQS risks introducing confusion to states in 

their attainment planning processes for this NAAQS and for other NAAQS as well, with little 

potential gain in return. In addition, the EPA does not believe it would be effective to 

include a series of subsections in this guidance, each providing specific guidance and specific 

factors for developing control measures for just a single specific category of emissions. To 

structure the document this way would result in a much larger and even more complex 

rulemaking, and simply would not be feasible. For this reason, we do not recommend adding 

any additional text to the preamble in response to comments 3 and 4.

Precursor Policy Options

1. Comment: Reviewer recommends providing clarification relating to PM2.5 precursor 

demonstration. Specifically, when conducting a PM2.5 precursor demonstration, would a 

state only consider emissions of a precursor in a nonattainment area for this 

demonstration? In this instance, is it assumed that if emissions of a precursor in the 

nonattainment area are not significant, then the state would not need to consider 

emissions of the PM2.5 precursor outside the nonattainment area unless attainment could 

not be demonstrated otherwise?

Response: Yes, the precursor demonstration options would be based on the evaluation of 

precursor emissions only from the nonattainment area. And yes, if emissions of a 

precursor in the nonattainment area are determined to not contribute significantly to 

PM2.5 levels in the area that exceed the standard, then the state would not need to 

consider emissions of the PM2.5 precursor outside the nonattainment area unless 

attainment by the Moderate area attainment date could not be demonstrated otherwise. 

We feel the preamble in the precursor section clearly states that the proposed options for 

evaluating significance are to be based on emissions from within the nonattainment area; 

for this reason, we do not think changes to the preamble are needed on this issue.