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 Environmental Protection Agency 40 CFR Part 52
[EPA-R08-OAR-2006-0952; FRL-9200-9]
 AGENCY: Environmental Protection Agency (EPA).
 ACTION: Proposed rule.
 SUMMARY: EPA is proposing to approve the State Implementation Plan (SIP) revision submitted by the State of Montana on March 26, 2008. Montana submitted this SIP revision to meet Clean Air Act requirements for attaining the 15.0 micrograms per cubic meter (μg/m3) annual fine Particulate Matter (PM2.5) national ambient air quality standard (NAAQS) for the Libby nonattainment area. The plan, herein called an “attainment plan,” includes an attainment demonstration, an analysis of Reasonably Available Control Technology and Reasonably Available Control Measures (RACT/RACM), base-year and projection year emission inventories, and contingency measures. The requirement for a Reasonable Further Progress (RFP) plan is satisfied because Montana projects that attainment with the 1997 PM2.5
                         NAAQS will occur in the Libby nonattainment area by April 2010. In addition, we are proposing to approve the PM10
                         SIP revisions to the Lincoln County Air Pollution Control Program submitted by Montana on June 26, 2006 for inclusion into Libby's attainment plan. This submittal contains provisions, including contingency measures, for controlling both PM10
                         and PM2.5
                         emissions from woodstoves, road dust, and outdoor burning. Finally, EPA is proposing to find on-road directly emitted PM2.5
                         and oxides of nitrogen (NOX) in the Libby, Montana nonattainment area insignificant for regional transportation conformity purposes. If this insignificance finding is finalized as proposed, the Libby, Montana nonattainment area will not have to perform a regional emissions analysis for either direct PM2.5
                         or NOX
                         as part of future conformity determinations for the annual 1997 PM2.5
                         NAAQS.
 DATES: Written comments must be received on or before October 14, 2010.
 ADDRESSES: Submit your comments, identified by Docket ID No. EPA-R08-OAR-2006-0952, by one of the following methods: http://*www.regulations.gov.*
                         Follow the on-line instructions for submitting comments.
                    *E-mail: freeman.crystal@epa.gov.*
                    *Fax:*
                         (303) 312-6064 (please alert the individual listed in 
                        **FOR FURTHER INFORMATION CONTACT**
                         if you are faxing comments).
                    *Mail:*
                         Callie Videtich, Director, Air Program, Environmental Protection Agency (EPA), Region 8, Mailcode 8P-AR, 1595 Wynkoop St., Denver, Colorado 80202-1129.
                    *Hand Delivery:*
                         Callie Videtich, Director, Air Program, Environmental Protection Agency (EPA), Region 8, Mail Code 8P-AR, 1595 Wynkoop St., Denver, Colorado 80202-1129. Such deliveries are only accepted Monday through Friday, 8 a.m. to 4:30 p.m., excluding Federal holidays. Special arrangements should be made for deliveries of boxed information. *Instructions:*
                         Direct your comments to Docket ID No. EPA-R08-OAR-2006-0952. EPA's policy is that all comments received will be included in the public docket without change and may be made available online at 
                        *http://www.regulations.gov,*
                         including any personal information provided, unless the comment includes information claimed to be Confidential Business Information (CBI) or other information whose disclosure is restricted by statute. Do not submit information that you consider to be CBI or otherwise protected through 
                        *http://www.regulations.gov*
                         or e-mail. The 
                        *http://www.regulations.gov*
                         Web site is an anonymous access system, which means EPA will not know your identity or contact information unless you provide it in the body of your comment. If you send an e-mail comment directly to EPA, without going through 
                        *http://www.regulations.gov,*
                         your e-mail address will be automatically captured and included as part of the comment that is placed in the public docket and made available on the Internet. If you submit an electronic comment, EPA recommends that you include your name and other contact information in the body of your comment and with any disk or CD-ROM you submit. If EPA cannot read your comment due to technical difficulties and cannot contact you for clarification, EPA may not be able to consider your comment. Electronic files should avoid the use of special characters, any form of encryption, and be free of any defects or viruses. For additional information about EPA's public docket, visit the EPA Docket Center homepage at 
                        *http://www.epa.gov/​epahome/​dockets.htm.*
                         For additional instructions on submitting comments, go to Section I, “General Information,” of the 
                        **SUPPLEMENTARY INFORMATION**
                         section of this document. *Docket:*
                         All documents in the docket are listed in the 
                        *http://www.regulations.gov*
                         index. Although listed in the index, some information is not publicly available, 
                        *e.g.,*
                         CBI or other information whose disclosure is restricted by statute. Certain other material, such as copyrighted material, will be publicly available only in hard copy. Publicly available docket materials are available either electronically in 
                        *http://www.regulations.gov*
                         or in hard copy at the Air Program, Environmental Protection Agency (EPA), Region 8, 1595 Wynkoop St., Denver, Colorado 80202-1129. EPA requests that, if at all possible, you contact the individual listed in 
                        **FOR FURTHER INFORMATION CONTACT**
                         to view the hard copy of the docket. You may view the hard copy of the docket Monday through Friday, 8 a.m. to 4 p.m., excluding Federal holidays.
 FOR FURTHER INFORMATION CONTACT: Crystal Freeman, Air Program, Environmental Protection Agency (EPA), Region 8, Mailcode 8P-AR, 1595 Wynkoop Street, Denver, Colorado 80202-1129, 
                        *Phone:*
                         (303) 312-6602, 
                        *Fax:*
                         (303) 312-6064, 
                        *freeman.crystal@epa.gov.*


SUPPLEMENTARY INFORMATION:  Definitions For the purpose of this document, we are giving meaning to certain words or initials as follows: (i) The words or initials 
                    *Act*
                     or 
                    *CAA*
                     mean or refer to the Clean Air Act, unless the context indicates otherwise. (ii) The words 
                    *EPA, we, us*
                     or 
                    *our*
                     mean or refer to the United States Environmental Protection Agency. (iii) The initials 
                    *SIP*
                     mean or refer to State Implementation Plan. (iv) The initials 
                    *PM*2.5
                     mean or refer to particulate matter with an aerodynamic diameter of less than 2.5 micrometers. (v) The initials 
                    *PM*10
                     mean or refer to particulate matter with an aerodynamic diameter of less than 10 micrometers. (vi) The word 
                    *State*
                     or 
                    *Montana*
                     refers to the State of Montana unless the context indicates otherwise. (vii) The initials 
                    *NAAQS*
                     mean or refer to National Ambient Air Quality Standards. 
                    ( print page 55714) Table of Contents I. General Information II. What Action Is EPA Proposing? III. What Is the Background for EPA's Proposed Action? A. Designation History B. Clean Air Fine Particle Implementation Rule IV. What Is Included in Montana's Submittal? A. Background B. PM10
                         SIP Revisions to the Lincoln County Air Pollution Control Program C. Libby and Vicinity PM2.5
                         Control Plan V. EPA's Analysis of Montana's Submittal A. PM10
                         SIP Revisions to Lincoln County Air Pollution Control Program B. Attainment Demonstration C. Analysis of Montana's Submittal 1. Pollutants Addressed and Attainment Date 2. Monitoring Data 3. Emission Inventory 4. Modeling 5. RACT/RACM 6. Contingency Measures 7. Transportation Conformity Requirements VI. Proposed Action VII. Statutory and Executive Order Reviews I. General Information A. What should I consider as I prepare my comments for EPA? 1. Submitting CBI. Do not submit this information to EPA through 
                    *http://www.regulations.gov*
                     or e-mail. Clearly mark the part or all of the information that you claim to be CBI. For CBI information in a disk or CD ROM that you mail to EPA, mark the outside of the disk or CD ROM as CBI and then identify electronically within the disk or CD ROM the specific information that is claimed as CBI. In addition to one complete version of the comment that includes information claimed as CBI, a copy of the comment that does not contain the information claimed as CBI must be submitted for inclusion in the public docket. Information so marked will not be disclosed except in accordance with procedures set forth in 40 CFR part 2. 2. 
                    *Tips for Preparing Your Comments.*
                     When submitting comments, remember to: a. Identify the rulemaking by docket number and other identifying information (subject heading, 
                    **Federal Register**
                     date and page number). b. Follow directions—The agency may ask you to respond to specific questions or organize comments by referencing a Code of Federal Regulations (CFR) part or section number. c. Explain why you agree or disagree; suggest alternatives and substitute language for your requested changes. d. Describe any assumptions and provide any technical information and/or data that you used. e. If you estimate potential costs or burdens, explain how you arrived at your estimate in sufficient detail to allow for it to be reproduced. f. Provide specific examples to illustrate your concerns, and suggest alternatives. g. Explain your views as clearly as possible, avoiding the use of profanity or personal threats. h. Make sure to submit your comments by the comment period deadline identified. II. What action is EPA proposing? EPA is proposing to approve two Montana SIP submittals for the Libby nonattainment area: (1) PM10
                     SIP revisions to the Lincoln County Air Pollution Control Program submitted by Montana on June 26, 2006; and (2) the Libby PM2.5
                     attainment plan submitted by Montana on March 26, 2008. EPA has determined that the PM10
                     SIP revisions and the PM2.5
                     attainment plan meet applicable requirements of the Clean Air Act, including the Clean Air Fine Particle Implementation Rule (herein referred to as the implementation rule) issued by EPA on April 25, 2007 (72 FR 20586). Furthermore, EPA has determined that Montana's PM2.5
                     SIP submittal for the Libby area includes an attainment demonstration, an analysis of RACT/RACM, base-year and projection-year emission inventories and contingency measures. The attainment plan supports a determination that the Libby PM2.5
                     nonattainment area will attain the 1997 PM2.5
                     NAAQS by the April 2010 deadline for attainment. Finally, EPA is proposing to find on-road directly emitted PM2.5
                     and NOX
                     in the Libby, Montana nonattainment area insignificant for regional transportation conformity purposes. EPA's analysis and findings are discussed in this proposed rulemaking. Additional technical support documents are available at 
                    *http://www.regulations.gov,*
                     Docket No. EPA-R08-OAR-2006-0952. III. What is the background for EPA's proposed action? A. Designation History On July 18, 1997 (62 FR 38652), EPA established PM2.5
                     NAAQS, including an annual standard of 15.0 μg/m3
                     based on a 3-year average of annual mean PM2.5
                     concentrations, and a 24-hour (or daily) standard of 65 μg/m3
                     based on a 3-year average of the 98th percentile of 24-hour concentrations. EPA established the standards based on significant evidence and numerous health studies demonstrating that serious health effects are associated with exposures to PM2.5. Following promulgation of a new or revised NAAQS, EPA is required by the CAA to designate areas throughout the United States as attaining or not attaining the NAAQS; this designation process is described in section 107(d)(1) of the CAA. In 1999, EPA and state air quality agencies initiated the monitoring process for the 1997 PM2.5
                     NAAQS, and, by January 2001, established a complete set of air quality monitors. On January 5, 2005, EPA published initial air quality designations for the 1997 PM2.5
                     NAAQS (70 FR 944), based on air quality monitoring data for calendar years 2001-2003. On April 14, 2005, EPA published a final supplemental rule amending the agency's initial designations (70 FR 19844). EPA did not consider modifications made in this rule to be “re-designations” because the changes were made before April 5, 2005, the effective date of the initial designations. As a result of the final supplemental rule, PM2.5
                     nonattainment designations are in effect for 39 areas, comprising 208 counties within 20 states (and the District of Columbia) nationwide, with a combined population of about 88 million people. The Libby nonattainment area which is the subject of this rulemaking is included in the list of areas not attaining the 1997 PM2.5
                     NAAQS. On October 17, 2006, EPA strengthened the 24-hour PM2.5
                     NAAQS to 35 μg/m3
                     and retained the level of the annual PM2.5
                     standard at 15.0 μg/m3
                     (71 FR 61144). On November 13, 2009 EPA designated areas as either attainment/unclassified or nonattainment with respect to the revised 24-hour NAAQS (74 FR 58688). In the November 2009 designation action, EPA established a deadline of December 14, 2012 for states to submit attainment plans for areas designated as nonattainment for the revised 24-hour PM2.5
                     NAAQS. Of relevance to the proposed rulemaking herein, the notice for the November 2009 action clarified designations for the 1997 PM2.5
                     NAAQS by relabeling the existing designation tables to identify designations for the annual NAAQS, and by providing a separate table identifying designations for the 1997 24-hour NAAQS (i.e., 65 μlg/m3). In that table, the Libby nonattainment area is designated as attaining the 1997 24-hour PM2.5
                     NAAQS. 
                    ( print page 55715) B. Clean Air Fine Particle Implementation Rule On April 25, 2007, EPA issued the Clean Air Fine Particle Implementation Rule for the 1997 PM2.5
                     NAAQS (72 FR 20586). The implementation rule describes the CAA framework and requirements for developing state PM2.5
                     attainment plans. An attainment plan must include a demonstration that a nonattainment area will meet applicable NAAQS within the timeframe provided in the statute. This demonstration must include modeling (40 CFR 51.1007) that is performed in accordance with EPA modeling guidance (EPA-454/B-07-002, April 2007). It must also include supporting technical analyses and descriptions of all relevant adopted federal, state, and local regulations and control measures that have been implemented by the proposed attainment date. For the 1997 PM2.5
                     NAAQS, an attainment plan must show that a nonattainment area will attain the standard by 2010. Alternatively, if the area is not expected to meet the NAAQS by 2010, a state may propose an attainment-date extension for up to five years based on the severity of the nonattainment problem and on the availability and feasibility of pollution control measures (CAA section 172(a)(2)). For each nonattainment area, the state must demonstrate that it has adopted all RACT/RACM needed to show that the area will attain the PM2.5
                     standards “as expeditiously as practicable.” The implementation rule provided guidance for making these RACM and RACT determinations (72 FR 20616-21). Any measures that are necessary to meet these requirements which are not already either federally promulgated or part of the state's SIP must be submitted in enforceable form as part of a state's attainment plan. The implementation rule also included policies on pollutants that comprise total PM2.5.
                     Five main types of pollutants contribute to fine particle concentrations: direct PM2.5, sulfur dioxide (SO2), nitrogen oxides (NOX), ammonia, and volatile organic compounds (VOCs). All but direct PM2.5
                     is considered to be “precursors” to PM2.5
                     formation. The effect of reducing emissions of each of these five types of pollutants varies by area, depending on PM2.5
                     composition, emission levels, and other area-specific factors. For this reason, the implementation rule established policies regarding what states should include in their PM2.5
                     attainment plans for evaluating these pollutants. Under these policies, sources of direct PM2.5
                     emissions (including organic particles, elemental carbon and inorganic particles) and SO2
                     must be evaluated for emission reduction measures in all PM2.5
                     nonattainment areas. Sources of NOX
                     must be evaluated for emission reduction measures in each area unless the state and EPA demonstrate that NOX
                     is not a significant contributor to PM2.5
                     concentrations in a specific area. Neither VOC nor ammonia sources are required to be evaluated for emission reduction measures in an area unless the state or EPA demonstrates that either of these pollutant types significantly contributes to PM2.5
                     concentrations. To reverse any of the presumptive precursor policies, the implementation rule provided guidance on the types of analyses that may be included in a technical demonstration. The implementation rule also provided guidance on other elements of a state's attainment plan, including but not limited to, consideration of emission inventories, contingency measures, and motor vehicle emissions budgets used for transportation conformity purposes. IV. What is included in Montana's submittal? A. Background Libby, Montana, a small rural community, is located in Lincoln County in the northwestern part of the State. Libby sits in the narrow, triangular Kootenai valley at an elevation of 2,100 feet. The nonattainment area is dominated by three major mountain ranges that limit the air-shed: (1) The Rocky Mountain and Flathead Ranges on the eastern boundary; (2) the Purcell Range, which roughly bisects the area from north to south; and (3) the Selkirk and Cabinet Ranges on the western boundary. The vast majority of the area surrounding Libby is National Forest managed by the U.S. Forest Service. Based on the 2000 census and a growth rate through 2005 of 3.71%, Libby's population is estimated at 2,674. The highest PM2.5
                     concentrations in Libby generally occur during the winter months of November through February. The winter concentrations are related to stagnant weather conditions dominated by light winds and strong temperature inversions. These meteorological conditions can trap emissions within the valley for many days or weeks. Air quality data recorded during 2001-2003 at the PM2.5
                     monitor at the Libby Courthouse Annex showed violations of the annual PM2.5
                     standard. Libby was designated nonattainment for PM2.5
                     under section 107(d)(3) of the CAA, on April 5, 2005 (40 CFR part 81). The air quality planning requirements for PM2.5
                     nonattainment areas are set out in Title I subpart 1 of the Act.[1] Historically, Libby was designated nonattainment for PM10
                     by operation of law on November 15, 1990 (56 FR 56694, 56794, November 6, 1991), under CAA section 107(d)(4)(B) and was classified as “Moderate.” The PM10
                     attainment plan was approved by EPA on August 30, 1994 (59 FR 44627). Montana has submitted revisions to the Lincoln County Air Pollution Control Program (herein referred to as the Program) and the Libby and Vicinity PM2.5
                     Control Plan (herein referred to as the Libby attainment plan) for the purpose of demonstrating attainment of the annual PM2.5
                     NAAQS. After public notice, public hearings regarding these two submittals were held on February 27, 2006 for the Lincoln County Air Pollution Control Program and on March 25, 2008 for the Libby and Vicinity PM2.5
                     Control Plan. The Montana Board of Environmental Review approved the revised Lincoln County Air Pollution Control Program on March 23, 2006 and the Libby attainment plan on March 25, 2008. Montana has met the requirements of Section 110(a)(2) for reasonable notice and public hearings. B. PM*10*
                     SIP Revisions to the Lincoln County Air Pollution Control Program Montana submitted revisions to the PM10
                     SIP for the Lincoln County Air Pollution Control Program for the Libby nonattainment area to improve and strengthen the PM10
                     attainment plan. The revisions include several provisions to regulate solid fuel burning devices and require owners and operators to obtain operating permits. Operating permits may only be issued for EPA-certified woodstoves or for pellet stoves. Furthermore, only specified materials can be burned in these devices, and visible emissions of greater than 20% opacity from them are prohibited. Additionally, these provisions allow for air pollution alerts if PM10
                     or PM2.5
                     concentrations averaged over a 4-hour period exceed a level 20 percent below any federal or state particulate matter standard. Provisions are also included for penalties for non-compliance and contingency measures. Additionally, revisions were made for open and outdoor burning regarding prohibited materials, major open burning and management burning, minor open burning or residential open 
                    ( print page 55716)
                    burning, and special burning. These revisions generally included significant limits on the time periods for open burning activities as compared to the existing PM10
                     SIP. Further restrictions also include prohibitions on burning from November 1 to March 31, which is the winter-time period when exceedances of PM2.5
                     typically occur. Lincoln County's Program prohibits burning the same materials as the State but is more restrictive because the burning of trade waste, Christmas tree waste, leaves, grass clippings and stumps is prohibited within the Air Pollution Control District [2]
                    
                     (herein referred to as the District). The June 26, 2006 submittal also included a stringency analysis for the Program showing that the revisions are more stringent than comparable State law. C. Libby and Vicinity PM*2.5*
                     Control Plan The Libby attainment plan provides a demonstration that the annual PM2.5
                     NAAQS will be met by April 2010 through the implementation of the Lincoln County Program described in section B above. The Libby attainment plan includes an emissions inventory (EI), a woodstove air pollution control calculation, and a technical analysis showing that the emissions of PM2.5
                     will be reduced sufficiently to meet the NAAQS. The key components of the Libby attainment plan are described as follows: 1. Ambient air quality monitoring in the Libby area began in 1999 and is conducted using Federal Reference Method (FRM) PM2.5
                     samplers at the Courthouse Annex site in downtown Libby. Based on monitoring data from the years 2001 to 2003, the 3-year annual design value was 15.9 μg/m3
                    , which is a violation of the annual PM2.5
                     NAAQS. In February 2002, speciation monitoring was conducted to determine possible PM2.5
                     emission sources. The results identified organic carbon as the main component of wintertime PM2.5
                     emissions. Further ambient monitoring was conducted from November 2003 to February 2004 to determine the geographic distribution of PM2.5
                     concentrations. After additional monitoring from various locations beyond Libby city limits and meteorological data from Libby Courthouse Annex site, it was determined that the Libby Courthouse Annex site represented the worst-case ambient PM2.5
                     levels in the area. 2. A chemical mass balance study (CMB) was conducted during the winter of 2003-2004 by the University of Montana, Center for Environmental Health Sciences (UM-CEHS). The goal of the CMB study was to identify those emission sources in the Libby area that contributed to elevated PM2.5
                     concentrations. The CMB model runs indicated that emissions from residential wood combustion were the major source of the fine particles on the PM2.5
                     filters, averaging 82% during the CMB study period (i.e., winter months). Other contributing PM2.5
                     sources identified by the CMB model were automobile exhaust (7%), ammonium nitrate (5%), diesel exhaust (4%), and sulfate (2%).[3] 3. Carbon 14 ([14]
                    C) analysis, as a part of the CMB study completed by UM-CEHS, was conducted by the University of Arizona's Accelerator Mass Spectrometry Laboratory Facility to provide further evidence that wood combustion was the major source of PM2.5
                     emissions in Libby.[4] 4. The Libby base year PM2.5
                     EI included a quantification of actual PM2.5
                     emissions and apportioned the emissions on a seasonal and annual basis for point and area sources. The State used calendar year 2005 as the base year for the development of an EI for the Libby area. The EI was used to support a proportional rollback model for the emission control plan. The State developed information for 2005 that allowed for the calculation of residential wood combustion and commercial fuel use. 5. The Libby PM10
                     SIP as revised also serves as the control plan for emissions of PM2.5. Controls exist for reducing emissions from re-entrained road dust through aggressive street sweeping and flushing, and traction sand durability requirements. Emissions of organic carbon are controlled through residential woodstove regulations and outdoor burning restrictions. 6. A significant part of the PM2.5
                     control strategies has been the completion of a woodstove changeout program. Approximately 1,130 uncertified woodstoves were replaced with EPA-certified woodstoves or pellet fuel burning devices. After the changeout, PM2.5
                     emissions have been reduced from approximately 138.78 tons/year to 57.21 tons/year, a decrease of 59%. PM2.5
                     control strategies are primarily focused on residential wood combustion. The control strategies also include: air pollution alerts may be declared during the winter months; solid fuel burning devices must have an operating permit; only EPA-certified woodstoves and pellet fuel burning devices can obtain permits; and only permitted pellet fuel devices can operate during air pollution alerts. Other control strategies for PM2.5
                     have included an expanded area for the prescribed burning control program and the continuing federal tailpipe standards. 7. Analysis for RACT/RACM was conducted for the Libby area. EPA's RACT/RACM guidance covers three general source categories: stationary, mobile and area (79 FR 20586). The Libby PM2.5
                     CMB study did not identify any emissions from local stationary sources, only a minor amount from mobile sources, and a significant amount from an area source category—residential wood combustion. EPA's area source RACM guidance covers four source categories: (1) Reduced solvent usage or solvent substitution; (2) controls on charbroiling or other commercial cooking operations; (3) controls on woodstoves and fireplaces; and (4) new or improved regulations on open burning (79 FR 20586 and 20621). The Libby attainment plan concluded that wood combustion control strategies and more stringent rules on open burning constituted RACM for area sources. The analysis further noted that the other two categories of area sources, commercial users of solvent and commercial cooking, were infrequent in the Libby area. The analysis also considered mobile sources, but determined that in light of their small contribution to PM2.5
                     nonattainment, existing federal tailpipe standards and natural turnover rates of the local vehicle fleet made additional measures for mobile sources unnecessary. 8. The Lincoln County Air Pollution Control Program is legally enforceable by Lincoln County, and by the State should Lincoln County fail to administer the program. The Libby attainment plan also provides for contingency measures if the NAAQS are exceeded after implementation. There is one contingency measure for wood burning for space heating purposes if it is determined that wood burning emissions contribute to an exceedance of the PM2.5
                     NAAQS, then only biomass pellet fuel burners may operate within the District. Other contingency measures are included for re-entrained dust and industrial facilities. There is also a review process to consider permanent adoption of a contingency measure. 
                    ( print page 55717) V. EPA's Analysis of Montana's Submittal A. PM*10*
                     SIP Revisions to Lincoln County Air Pollution Control Program EPA's summary of the PM10
                     SIP revisions is addressed in detail under section IV.B. These revisions were made for two purposes: (1) To address PM2.5
                     attainment plan requirements; and (2) to improve and strengthen requirements for continued attainment of PM10
                    . The revisions are a significant improvement to a plan that was approved by EPA 16 years ago. The Libby area has not had an exceedance of the PM10
                     NAAQS since 1993. Furthermore, clarifications were made to the language to better explain to the public the requirements of the air quality program. The revisions removed exemptions and replaced them with requirements for obtaining permits for wood burning appliances. These revisions also added enforcement provisions where previously none had existed. Section 110(l) of the Clean Air Act states that a SIP revision cannot be approved if the revision would interfere with any applicable requirement concerning attainment and reasonable further progress toward attainment of the NAAQS or any other applicable requirement of the Act. The Libby area is currently meeting the NAAQS for all criteria pollutants and has not had any violations of the PM10
                     standard for over a decade. Furthermore, the revisions do not relax the stringency of any SIP provision; in fact, the revisions generally strengthen the SIP. As a result, the PM10
                     SIP revisions do not interfere with attainment of the NAAQS or any other applicable requirement of the Act. Therefore, section 110(l) requirements are satisfied. B. Attainment Demonstration In accordance with section 172(c) of the CAA and the implementation rule, the attainment plan submitted by Montana for the Libby area included: (1) Emission inventories for the plan's base year (2005) and projection year (2009); and (2) an attainment demonstration consisting of: (a) Technical analyses that locate, identify, and quantify sources of emissions contributing to violations of the annual PM2.5
                     NAAQS; (b) analyses of future-year emission reductions and air quality improvements expected to result from national and local programs, and from new measures to meet RACT/RACM requirements; (c) adopted emission reduction measures; and (d) contingency measures. C. Analysis of Montana's Submittals 1. Pollutants Addressed and Attainment Date In accordance with policies described in the implementation rule, Montana's PM2.5
                     attainment plan evaluates emissions of direct PM2.5, SO2
                     and NOX
                     in the Libby area. Montana provided documentation of expeditious attainment of the annual PM2.5
                     NAAQS in the Libby area by April 2010. Areas that demonstrate attainment by 2010 are considered to have satisfied the requirement to show reasonable further progress toward attainment and need not submit a separate RFP plan. For similar reasons such areas are also not subject to a requirement for a mid-course review. Montana's evaluation of emissions is based on the work conducted by UM-CEHS for the CMB model runs indicating that emissions from residential wood combustion were the major source (82%) of the fine particles on the PM2.5
                     filters. Other PM2.5
                     sources identified by the CMB model were automobile exhaust (7%), ammonium nitrate (5%), diesel exhaust (4%), and sulfate (2%). In addition, a Carbon 14 analysis confirmed that wood combustion is the major source of PM2.5
                     emissions in the Libby area and that emissions of both SO2
                     and NOX
                     are very minor compared to PM2.5
                     emissions from residential wood combustion. As described in the emissions inventory, the sources of SO2
                     are from home heating oil and sources of NOX
                     are from on-road and off-road mobile sources (see further discussion in section V.C.7. on NOX
                     emissions from mobile sources). 2. Monitoring Data As shown in the table below, the annual weighted average for 2009 shows that the Libby area has met the April 2010 deadline for the 1997 PM2.5
                     NAAQS. The trend in annual average concentrations is downward and coincides with the implementation of the woodstove changeout program. This is based on quality-controlled and quality-assured monitoring data from 2005-2009 that is available in the EPA Air Quality System (AQS). Table V.2-1
Year
Annual weighted average 
                             
                                (μg/m3
                                )2005
15.82006
15.22007
13.02008
12.92009
10.7
 3. Emission Inventory CAA section 172(c)(3) states that for nonattainment areas, the State shall prepare a statewide emission inventory no later than three years after designation. The baseline emission inventory for calendar year 2005 or another suitable year shall be used for attainment planning (40 CFR 51.1008(b)). EPA promulgated the Air Emissions Reporting Rule (AERR) (40 CFR part 51, subpart A) in order to consolidate the various reporting requirements that already exist, including those requirements outlined in the PM2.5
                     implementation rule. The AERR requires states to report state-wide emissions every three years. Montana prepared a statewide emission inventory for 2005. This inventory included annual totals of emissions of criteria pollutants and their precursors. The State used data from this statewide inventory to create an emission inventory specific to the Libby area. Monitoring data for 2005 showed an exceedance of the PM2.5
                     annual standard. The year 2005 is a suitable year for attainment planning because an emission inventory for this year is representative of ambient emission levels that led to the exceedance of the annual standard. The 2005 emission inventory showed that residential wood burning comprised 82% of the direct PM2.5
                     emissions during the winter. The next largest direct source, road dust, was 11%, followed by locomotive emissions at 3.4%. The remaining criteria pollutant emissions were very minor, including the precursors of PM2.5
                     (i.e., NOX
                     and SO2). Background values of PM2.5
                     were accounted for by the State using monitored data collected at remote stations far away from emissions sources in the Libby area. EPA notes that the State used a conservative emission inventory approach for projecting future growth for the 2010 attainment year which involved increasing the vehicle emissions by 2.1% (the population growth rate) from the 2005 base year inventory, and not taking any credit for potential emission reductions that may have been available from fleet turnover and the Federal tailpipe standards for vehicles. Condensable particulate matter was not considered in the emission inventory because of a lack of sources in the Libby area. 4. Modeling CAA Section 172(c) requires states with nonattainment areas to submit an attainment demonstration. A PM2.5
                     attainment demonstration consists of (1) analyses which estimate whether 
                    ( print page 55718)
                    selected emissions reductions will result in ambient concentrations that meet the NAAQS and (2) a set of control measures which will result in the required emissions reductions. Montana's analysis of future-year emissions reductions and air quality improvements was based on a proportional rollback model for showing attainment of the standard and a roll forward model demonstrating attainment in the future. The proportional models were applied in conjunction with the findings from chemical mass balance and Carbon 14 studies conducted by the University of Montana. In the particular case of Libby, a proportional model is more appropriate than dispersion models. The great majority of periods with elevated PM2.5
                     concentrations in Libby occur during wintertime stagnation conditions. Furthermore, dispersion in Libby is constrained by steep terrain. The most suitable approach for stagnation conditions should be determined on a case-by-case basis, (see sections 7.2.8 and 8.3.4.2(b) of the Guideline on Air Quality Models, 40 CFR part 51, appendix W), and an alternative model should be selected by the EPA Regional Office when a preferred model is less appropriate (see section 3.2.2 of the Guideline). The proportional model used the emission inventory for 2005 when there was an exceedance of the standard. The decrease in PM2.5
                     emissions for the Libby area resulting from the woodstove changeout program was calculated based on the amount of wood burned by the EPA-certified woodstoves and then compared to the amount of emissions resulting from burning the same amount of wood from the uncertified woodstoves that were still in use. The decrease in emissions would be an indication of the effectiveness of the control strategy. Montana estimated that PM2.5
                     emissions would be reduced by 81.57 tons as a result of the new EPA-certified woodstoves installed in Libby households. The State projected future annual average PM2.5
                     concentrations for Libby at 9.5 μg/m3
                    . This projection was based on the installation of the new stoves and a 100 percent compliance with the wood burning restrictions for Libby. EPA's guidance is based on emission sources complying with state and local restrictions on emission sources (Emissions Inventory Guidance for Implementation of Ozone and Particulate Matter National Ambient Air Quality Standards (NAAQS) and Regional Haze Regulations, appendix B, EPA-454/R-05-001, August 2005.) The guidance defines rule effectiveness (RE) as a method to account for the reality that not all emission sources are in compliance 100% of the time. The guidance provides a listing of the factors that are most likely to affect RE. EPA used a conservative 70% RE instead of a 100 percent compliance to determine if Libby would still reach attainment of the PM2.5
                     standard. EPA estimated that using the more conservative compliance percentage for wood burning restrictions, the future value for Libby would still be below the PM2.5
                     standard of 15 μg/m3
                    . As stated above in Table V.2.-1 the Libby area 2009 annual average is currently 10.7 μg/m3
                    . 5. RACT/RACM Determination of RACT/RACM is a three-step process: (1) Identifying potential measures that are reasonable; (2) modeling to identify the attainment date that is as expeditious as practicable; and (3) selecting RACT/RACM. Identification of potential measures should ordinarily be supported by an inventory of emissions of directly emitted PM2.5
                     and of precursors from the relevant sources and source categories; the technologically feasible control measures for each source or source category; and, for each measure, the control efficiency, possible emission reductions by pollutant, estimated cost per ton, and the date by which the measure was or could be implemented; and other relevant information. For the first step, identification of potential measures that are reasonable, Montana supported its RACT/RACM analysis with the emissions inventory and the CMB study. The RACT/RACM analysis first noted that there are no major stationary sources of PM2.5
                     in the Libby area. It also noted that minor stationary sources are currently regulated under Montana's minor source program, which requires permits and a Best Available Control Technology (BACT) review. As discussed in the implementation rule, if state or federal rules already regulate a given sector, it is reasonable for a state to look to unregulated sectors for RACT/RACM measures. Furthermore, the implementation rule permits the state to use reason in the extent of its effort to identify potential control measures. For example, the rigor of the analysis may depend on the relative contribution of a particular pollutant to the PM2.5
                     nonattainment problem (72 FR 20613). As shown by the CMB study, stationary sources are a very minor contributor to PM2.5
                     nonattainment in Libby. Similarly, the RACT/RACM analysis reasoned that mobile sources are currently regulated, make only a minor contribution to the nonattainment problem, and the overall emissions will continue to be reduced through fleet turnover. Thus, the first step focused on measures for area sources. The analysis further noted that two types of area sources (commercial users of solvents and commercial charbroilers or other commercial cooking operations) were infrequent in the Libby area. The analysis also discussed re-entrained road dust, which the CMB study did not identify as a contributor to PM2.5
                     nonattainment, and noted that there were existing SIP provisions to control road dust. As to home heating oil, a source of SO2, the CMB study found only a 2% contribution to PM2.5
                     nonattainment for all sulfates combined. Thus, the RACM analyses focused on the remaining area sources of wood burning devices and open burning and identified several control measures to be included in the attainment plan. For the second step, as discussed in more detail in section V.C.4, Montana modeled attainment by 2010 based on adoption of these reasonable control measures. Finally, for the third step, based on the analysis, Montana selected and adopted RACM for wood burning devices and open burning. For wood burning devices, the State developed and implemented a woodstove changeout control strategy. The woodstove changeout permanently removed 1,130 old, uncertified woodstoves and replaced them with EPA-certified woodstoves or pellet stoves. Additionally, the State adopted measures that require permits for solid fuel burning devices (including woodstoves) and restrict installation and operation of these devices to three categories: pellet stoves, devices with a catalytic emissions control system, and devices with a non-catalytic emissions control system. For the latter two, emission limits are imposed. RACM measures were also included for major open burning, management burning, residential burning, and special burning. The PM2.5
                     attainment plan includes BACT and permits for an expanded area, which is the entire Air Pollution Control District, for all of these different types of burning activities. Additionally, these burning activities were restricted to shorter time periods. In summary, the State evaluated, by source category, sources of direct PM2.5, SO2
                     and NOX
                     for RACT/RACM control measures. The State's evaluation of sources of SO2
                     and NOX
                     resulted in their decision that no additional controls are necessary to attain the 
                    ( print page 55719)
                    NAAQS based on the absence of major sources or area sources that can be cost effectively or reasonably controlled. The State therefore adopted RACM for direct PM2.5. In accordance with Section 172(c) of the CAA, Montana has adopted all RACT/RACM needed to attain the standards as expeditiously as practicable. EPA has reviewed Montana's RACT/RACM analysis and has determined that the state reasonably identified potential control measures, modeled the attainment date that is as expeditious as practicable and reasonably selected RACT/RACM for the Libby area. 6. Contingency Measures In conformance with Section 172(c)(9) of the CAA, the implementation rule requires that PM2.5
                     attainment area plans include contingency measures. These measures must be fully adopted or otherwise ready for quick implementation, should contain trigger mechanisms and an implementation schedule, should be measures not included in the SIP control strategy, and should provide the equivalent of one year of RFP. Once triggered, a contingency measure should take effect without further action by the State or EPA. The Libby SIP contains contingency measures for residential wood burning, re-entrained dust, and industrial facilities. If it is determined that residential wood burning contributes to an exceedance of the PM2.5
                     NAAQS, then only biomass pellet fuel burners may operate within the District. If re-entrained dust contributes to noncompliance, then the existing regulations (which currently only apply in a limited area) are made applicable to the entire Air Pollution Control District. Finally, if an industrial facility contributes to noncompliance, the Montana Department of Environmental Quality (MTDEQ) will initiate contingency measures to reduce emissions. Once a contingency measure is initiated, it must remain active until the Libby SIP demonstration is revised and resubmitted to EPA for approval. The contingency measures for residential wood burning and re-entrained dust meet the requirements of the implementation rule. The contingency measure for major point sources would require further action by MTDEQ to determine whether additional controls are necessary. However, the contingency measures for residential wood burning and re-entrained dust are sufficient to meet the requirements of the CAA, including equivalence to one year of RFP. 7. Transportation Conformity Requirements Transportation conformity is required under CAA section 176(c) (42 U.S.C. 7506(c)) to ensure that transportation plans, transportation improvement programs (TIPs) and federally supported highway and transit projects are consistent with (“conform to”) the state air quality implementation plan. Transportation conformity applies to areas that are designated nonattainment, and to those areas redesignated to attainment after 1990 with a CAA section 175A maintenance plan (“maintenance areas”), for transportation-related criteria pollutants: carbon monoxide (CO), NOX
                     and particulate matter (PM2.5
                     and PM10). EPA's transportation conformity rule (40 CFR parts 51 and 93) establishes the criteria and procedures for determining whether transportation activities conform to the SIP. One requirement of the rule is that transportation plans, TIPs, and projects must satisfy a regional emissions analysis for the relevant pollutants and precursors (40 CFR 93.118, 119). However, section 93.109(m) of this rule states that an area is not required to satisfy a regional emissions analysis for a pollutant or precursor if the SIP demonstrates that motor vehicle emissions of that pollutant or precursor are an insignificant contributor to the area's air quality problem. In today's notice, EPA is proposing to find that motor vehicle emissions of PM2.5
                     and NOX
                     are insignificant contributors to Libby's PM2.5
                     nonattainment problem. If this proposal is finalized, PM2.5
                     and NOX
                     motor vehicle emissions budgets (MVEB) would not be established and a regional emissions analysis would not be required for either PM2.5
                     or NOX
                     in any future conformity determination in Libby. Please note, however, that this proposed action would not apply to PM2.5
                     hot-spot analyses for individual projects, if such an analysis is required in the future for transportation conformity purposes. There are specific transportation conformity provisions that EPA proposes to determine as applicable to the Libby PM2.5
                     nonattainment area. As provided in more detail in 40 CFR 93.109(m), these specific conformity provisions are addressed when EPA finds that emissions from motor vehicles in the Libby PM2.5
                     nonattainment area are an insignificant contributor to the areas' nonattainment problem for a relevant NAAQS and/or precursor. To consider making such an insignificant finding, EPA evaluated the provisions of 40 CFR 93.109(m) against the relevant information contained in the SIP attainment plan, the SIP revision's associated technical support document (TSD), and additional information as developed by EPA. We evaluated the following factors in determining whether on-road direct PM2.5
                     and NOX
                     emissions are insignificant contributors to the area's PM2.5
                     air quality problem; (1) the percentage of motor vehicle emissions in the context of the total SIP inventory; (2) the current state of air quality as determined by monitoring data for that NAAQS; (3) the absence of SIP motor vehicle control measures; and (4) historical trends and future projections of the growth of motor vehicle emissions. Our evaluation and conclusions are as follows: a. The Percentage of PM2.5
                     Motor Vehicle Emissions in the Context of the Total SIP Inventory This factor, with regard to PM2.5
                     emissions, is addressed in two areas of the SIP revision documentation. Table 27.12.11.4B (“PM2.5
                     Annual Demonstration of Compliance”) of the Libby attainment plan provides relevant information with regard to 2003-2004 CMB percentages by source category, percent reduction in emissions due to control strategies, estimated growth in emissions over the 2005 to 2010 time period, and 2010 compliance year contributions. The dominant CMB source was residential woodstoves at 82% with motor vehicle tailpipe emissions at 7% of total PM2.5
                     mass and diesel exhaust at 4% of the total PM2.5
                     mass. The contribution of motor vehicle PM2.5
                     emissions is also documented in Table 5.1A (“Seasonal PM 2.5 Emissions in Libby by Source Category”) of the SIP's TSD. Table 5.1A presents estimated emissions based on metric tons and percentage of the inventory for 2005, by season; we have provided these motor vehicle tailpipe PM2.5
                     emissions, as percent of total PM2.5
                     emissions, in Table V.7-1 below. We note that in Table 5.1A of the SIP's TSD, the inventory is dominated by woodstove emissions in all four seasons. 
                    ( print page 55720) Table V.7—1 Motor Vehicle PM2.5
                         Emissions Percentage of Total Inventory for 2005
(All figures are in metric tons)
Season
Motor vehicle PM2.5
                             emissions
Total inventory PM2.5
                             emissions
Motor vehicle emissions % of totalWinter
0.48
80.63
0.59Spring
0.55
46.43
1.18Summer
0.66
13.66
4.83Fall
0.51
97.67
0.52Total Year
2.2
238.38
0.92
 As shown in Table V.7.-1 above, motor vehicle tailpipe PM2.5
                     emissions represent an annual average of only 0.92% of the total PM2.5
                     inventory. That is, motor vehicle emissions are less than one percent of the inventory over the course of a year. During the summer, motor vehicle emissions make up close to five percent of the inventory, but motor vehicle emissions are only slightly higher during the summer than during other seasons. The motor vehicle emissions percentage is much greater during the summer compared with other seasons primarily because total PM2.5
                     emissions are significantly reduced during the summer compared to other seasons; summer is the season with the fewest emissions from woodstoves. The information provided in the State's submittal supports a conclusion that regional PM2.5
                     on-road mobile source emissions are a minimal percentage in the context of the total PM2.5
                     emissions inventory. Therefore, this factor supports the proposed finding that on-road PM2.5
                     emissions are insignificant for the Libby PM2.5
                     nonattainment area. b. The Current State of Air Quality as Determined by Monitoring Data for the PM2.5
                     NAAQS This factor is addressed as shown in the table below. From the State's SIP revision and section V.B.2 above, from 2007 to 2009 the Libby area continues to demonstrate attainment of the 1997 annual PM2.5
                     NAAQS. Furthermore, the trend in annual average concentrations is downward and coincides with the implementation of the woodstove changeout program. This data is based on quality-controlled and quality-assured monitoring data from 2005-2009 that are available in the EPA AQS. This factor supports the proposed finding that on-road PM2.5
                     emissions are insignificant for the Libby PM2.5
                     nonattainment area. Table V.2.-1
Year
PM2.5
                             annual weighted average
                             (μg/m3)2005
15.82006
15.22007
13.02008
12.92009
10.7
 c. The Absence of SIP Motor Vehicle Control Measures for PM2.5 The Libby PM2.5
                     attainment plan relies on a 59% reduction in residential woodstove emissions to reach attainment of the annual PM2.5
                     NAAQS and took no credit for any emission reductions in the motor vehicle tailpipe and diesel exhaust categories (
                    *e.g.*
                     Federal tailpipe emission standards and fleet turnover). The State further described these assumptions in sections 27.12.7.3 (“Federal Tailpipe Standards Control Program”) and 27.12.11.4 (“PM2.5
                     2010 Demonstration of Compliance”) of the Libby attainment plan. EPA also notes there is no State or local mandated motor vehicle emission control requirements (
                    *e.g.,*
                     inspection and maintenance program, fuels, or transportation control measures) for the Libby PM2.5
                     nonattainment area. Therefore, this factor supports the proposed finding that on-road PM2.5
                     emissions are insignificant for the Libby PM2.5
                     nonattainment area. d. Historical Trends and Future Projections of the Growth of Motor Vehicle PM2.5
                     Emissions Libby's annual PM2.5
                     2001-2003 design value was 15.9 μg/m3
                    . In November 2003 through February 2004 air quality data was collected in Libby to support CMB modeling. This CMB modeling showed that residential wood smoke was the primary source of PM2.5
                     in Libby. Table 27.12.11.4B in the Libby attainment plan shows that, when the results of the CMB modeling are applied to the air quality data from 2001-2003, residential wood smoke contributed 13.0 μg/m3
                     (82%) of the 2001-2003 annual PM2.5
                     design value, motor vehicle tailpipe emissions contributed 1.1 μg/m3
                     (7%), and diesel exhaust emissions contributed 0.7 μg/m3
                     μg/m3
                     (4%). Based on the results of this modeling Montana based its attainment strategy for the area on a woodstove change-out program. The SIP assumes that the woodstove change-out program will reduce those emissions by 59% in 2010. The SIP also assumes that motor vehicle tailpipe emissions and diesel exhaust emissions would grow by 2.1% between 2005 and 2010, which is equal to the expected population growth rate during that period. The SIP does not account for any reductions in motor vehicle emissions or diesel exhaust that would occur due to fleet turnover to new lower emission motor vehicles, on-road diesel vehicles or off-road equipment. Table 27.12.11.4B in the Libby attainment plan shows that in 2010 the predicted annual average PM2.5
                     concentration would be 8.37 μg/m3
                    . The table also shows that residential wood smoke is expected to contribute 5.44 μg/m3
                     (65%) in 2010, motor vehicle tailpipe emissions would contribute 1.12 μg/m3
                     (13%), and diesel exhaust emissions would contribute 0.71 μg/m3
                     (8%). As can be seen, on a percentage basis the contribution of motor vehicle emissions and diesel exhaust increases; however, overall PM2.5
                     concentrations are expected to decrease by 53% to 8.37 μg/m3
                    , the contribution of wood smoke emissions is expected to decrease by 59%, and the total contribution of emissions from motor vehicles and diesel exhaust to PM2.5
                     mass in 2010 is expected to increase by only 0.03 μg/m3
                     between 2005 and 2010. This increase in mass is due to the assumptions that emissions from these sources increase at the same rate as population growth and that no emissions reductions from fleet turnover are included in the calculations. Both of these are conservative assumptions. EPA notes that the contribution of motor vehicle emissions of 13% to PM2.5
                     mass in 2010 represents the projected chemical mass balance of PM2.5
                     and not an emission inventory projection. The 
                    ( print page 55721)
                    SIP includes a base year PM2.5
                     inventory (Table 5.1A) for 2005. That inventory shows that motor vehicle emissions of PM2.5
                     are 2.20 tpy and that total PM2.5
                     emissions in the base year are 238.39 tpy. Therefore, the motor vehicle emissions in the base year are slightly less than 1% of the total direct PM2.5
                     emissions. On the surface this may seem to be in conflict with the results of the CMB modeling, which shows that motor vehicle exhaust contributed about 7% of the PM2.5
                     mass in the base year. However, it should be noted that the chemical mass balance data and the PM2.5
                     data collected at the Libby Courthouse Annex represents only one receptor within the City of Libby, and only for the period of late 2003 through early 2004. While this location is believed to be representative of Libby's air quality, numerous factors influence the local particulate matter concentrations and air quality. Local scale meteorology (wind speed, wind direction, temperature, relative humidity, barometric pressure, and solar radiation at a minimum), traffic patterns, and precipitation are a few examples of these factors which vary throughout the city. Accepting that variable conditions exist throughout Libby, as well as the inherent uncertainty associated with ambient air monitoring, the difference that exists between PM2.5
                     monitoring data at one receptor and a city-wide emission inventory appears to be plausible. We also note that the actual location of the monitor may have exposed it to additional influence from motor vehicle emissions. We have not performed an in-depth analysis, but we do note that the monitor is located directly adjacent to U.S. Highway 2, the main north/south highway through Libby. Although motor vehicle PM2.5
                     emissions are shown to be minimal in the State's emissions inventory (ref. Table 5.1A: “Seasonal PM2.5
                     Emissions in Libby by Source Category” and Table V.7.-1 above), motor vehicle emissions may have shown a greater than anticipated contribution on the chemical mass balance analysis due to the monitor's close proximity to Highway 2. Overall, this factor supports the proposed finding that on-road PM2.5
                     emissions are insignificant for the Libby PM2.5
                     nonattainment area. In summary, all four factors support the proposed finding. After weighing these four factors described in 40 CFR 93.109(m) and evaluated above, EPA proposes to find that on-road PM2.5
                     emissions are insignificant for the Libby PM2.5
                     nonattainment area. We turn to applying the four factors to on-road NOX
                     emissions. e. The Percentage of NOX
                     Motor Vehicle Emissions in the Context of the Total SIP Inventory The Libby attainment plan focuses on directly emitted PM2.5
                     and controls of PM2.5
                     emissions from woodstoves and does not address any motor vehicle NOX
                     emissions other than to indicate in Table 27.12.11.4B “PM2.5
                     Annual Demonstration of Compliance” that the CMB data show that ammonium nitrate was only 5% of the mass found on the filters. EPA, therefore, drew upon other relevant, available data to evaluate whether NOX
                     motor vehicle emissions in the Libby PM2.5
                     nonattainment area are significant and require that a NOX
                     motor vehicle emissions budget be established for transportation conformity purposes or whether on-road NOX
                     emissions could be found insignificant based on the criteria in 40 CFR 93.109(m). EPA reviewed relevant information from EPA's National Emissions Inventory (NEI) data for 2005 that were used for the 2009 final designations for the 24-hour 2006 PM2.5
                     NAAQS (74 FR 58688, November 13, 2009).[5]
                    
                     However, since the NEI data were for Lincoln County as a whole, we needed to assess how much of the Lincoln County on-road NOX
                     inventory could be apportioned to the Libby PM2.5
                     nonattainment area. Our methodology was to calculate how many vehicle miles traveled (VMT) the Libby PM2.5
                     nonattainment area contributes to Lincoln County's total VMT and to assign that same proportion of the total Lincoln County on-road NOX
                     emissions to the Libby PM2.5
                     nonattainment area, as explained further below. We then needed to determine what percentage this was of total NOX
                     from the Libby PM2.5
                     nonattainment area. Specific emissions data for Lincoln County, MT, which includes the Libby PM2.5
                     nonattainment area, are presented in Table V.7.-2 below and are from EPA's PM2.5
                     24-hour 2006 NAAQS final designations information. Table V.7.-2—(All emission figures are in tons per year)
County
Major category
VOC
NOX
SO2
NH3
PM2.5
OC
EC
SO4
NO3
PMFineLincoln
Fires
6106
310
277
425
2199
1286
219
20
10
664Lincoln
Non-Road
338
2403
169
1
76
16
55
0
0
4Lincoln
On-Road
366
545
15
23
11
3
6
0
0
2Lincoln
Other-Stationary
871
138
74
57
453
108
16
5
1
323Total

7681
3395
535
506
2738
1412
296
25
11
994
 The “On-Road” or motor vehicle, 2005 NEI emissions were calculated by EPA for Lincoln County based on a county annual total of VMT of 231,246,800. This VMT figure, which represents data for the entire county, is also referenced in our 2006 PM2.5
                     24-hour NAAQS final designations information.[6] Based on the 2005 NEI data referenced above in Table V.7.-2, Lincoln County's total annual VMT of 231,246,800 results in approximately 545 tpy of on-road NOX
                    . To calculate the estimated on-road NOX
                     emissions for the Libby PM2.5
                     nonattainment area, we first needed to determine what percentage of Lincoln County's total VMT is attributed to the Libby PM2.5
                     nonattainment area. We then applied that VMT percentage to the total Lincoln County on-road NOX
                     emissions to get the estimated on-road NOX
                     emissions for the Libby PM2.5
                     nonattainment area. The total VMT for the Libby PM2.5
                     nonattainment area, 54,877,360, came from the MTDEQ.[7]
                    
                     This is 23.73% of Lincoln County's total VMT (i.e., 54,877,360 VMT from Libby divided by 231,246,800 VMT from Lincoln County as a whole). It is reasonable to assume that the Libby PM2.5
                     nonattainment area contributes this same percentage of on-road NOX
                     emissions to the total Lincoln County on-road NOX
                     emissions. Therefore, we applied this 23.73% to the Lincoln County total of 545 tpy of 
                    ( print page 55722)
                    on-road motor vehicle NOX
                     emissions, which results in approximately 129.33 tpy of on-road NOX
                     emissions for the Libby PM2.5
                     nonattainment area. In lieu of other specific data, EPA considers this approach a reasonable estimate of the on-road NOX
                     emissions for the Libby PM2.5
                     nonattainment area. Once we had a figure for the number of tons of on-road NOX
                     emissions from Libby, the next step in our analysis was to determine what percentage of the total anthropogenic NOX
                     this represents. Again, since the NEI data available were for Lincoln County as a whole, we needed to assess how much of the Lincoln County total anthropogenic NOX
                     could be apportioned to the Libby PM2.5
                     nonattainment area. To do so, we needed to establish what NOX
                     emissions were from anthropogenic sources in the Libby PM2.5
                     nonattainment area other than from on-road motor vehicle tailpipes. To develop these particular emissions figures, we assumed that the percentage of Lincoln County's anthropogenic NOX
                     coming from Libby would be the same as the percentage of Lincoln County's anthropogenic PM2.5
                     emissions coming from Libby, as described below. First, we determined the anthropogenic NOX
                     emissions for Lincoln County from the “Non-Road” and “Other Stationary” source categories. We used the data from Table V.7.-2 above and eliminated the “Fires” [8]
                    
                     and “On-Road” emissions categories from the Lincoln County 2005 NEI data (
                    *see*
                     Table V.7.-3 below): Table V.7.-3—(All emissions are in tons per year)
County
Major category
VOC
NOX
SO2
NH3
PM2.5
OC
EC
SO4
NO3
PM FineLincoln
Non-Road
338
2403
169
1
76
16
55
0
0
4Lincoln
Other-Stationary
871
138
74
57
453
108
16
5
1
323Total

1209
2541
243
58
529
124
71
5
1
327
 The total anthropogenic NOX
                     in Lincoln County from sources other than on-road is 2541 tpy. Next, we summed-up the PM2.5
                     emissions from the Libby PM2.5
                     nonattainment area from the State's SIP emission inventory Table 5.1A, but did not include emissions from fires (
                    *i.e.,*
                     PM2.5
                     emissions from “Large Prescribed Burning” and “General Burning” were not included from the State's Table 5.1A); 
                    *see*
                     Table V.7.-4 below. Table V.7.-4—Libby Anthropogenic PM2.5
                         Emissions
(As adapted from Table 5.1A “Seasonal PM2.5
                         Emissions in Libby by Source Category” of the Libby Attainment SIP Emission Inventory)
Sources
Winter
Spring
Summer
FallWoodstoves Residential/Com.
66.65
20.74
5.08
58.76Paved Roads Fugitive Dust
8.92
2.57
3.23
9.61Large Prescribed Burning
- - -
- - -
- - -
- - -General Burning
- - -
- - -
- - -
- - -Locomotives
2.72
2.72
2.72
2.72Unpaved Roads Fugitive Dust
1.22
1.34
1.53
1.2Propane Heating Residential/Com.
0.13
0.04
0.01
0.11Oil Heating Residential/Com.
0.48
0.15
0.04
0.42Aircraft
0.0
0.03
0.03
0.0Road & Building Construction Dust
0.02
0.36
0.36
0.36Motor Vehicle Tailpipe
0.48
0.55
0.66
0.51Total (Metric Tons)
80.62
28.50
13.66
73.69Total Short Tons (2000 lbs. per ton)
88.88
31.42
15.06
81.24Total Annual Anthropogenic Short Tons of PM2.5
                         Emissions = 216.60 tons.
 Based on the data in Table V.7.-4 above, the total annual anthropogenic short tons of PM2.5
                     emissions (without including emissions from the “Motor Vehicle Tailpipe” category) from “Non-Road” and “Other Stationary” sources in the Libby PM2.5
                     nonattainment area are estimated as 214.17 tons per year. The Libby PM2.5
                     nonattainment area's annual emissions of PM2.5
                     from “Non-Road” and “Other Stationary” anthropogenic sources is 214.17 tpy, whereas these sources emit 529 tpy for Lincoln County as a whole (see Table V.7.-3 above). Therefore, Libby's share of Lincoln County's PM2.5
                     emissions from “Non-Road” and “Other Stationary” anthropogenic sources is approximately 40.48%. We then added Lincoln County NOX
                     emissions from the “Non-Road” and “Other Stationary” sources categories, 2541 tpy (see Table V.7-3 above), and attributed 40.48% of those emissions to the Libby PM2.5
                     nonattainment area's NOX
                     “Non-Road” and “Other Stationary” sources categories, which results in 1028.6 tpy. To summarize, EPA estimated the Libby PM2.5
                     nonattainment area's on-road NOX
                     motor vehicle emissions as 129.33 tpy, and the non-road and other stationary sources' NOX
                     emissions as 1028.6 tpy. Therefore, the total estimated annual anthropogenic NOX
                     emissions from all of these source categories are estimated to be 1157.93 tpy for the Libby PM2.5
                     nonattainment area. The approximate contribution of annual on-road NOX
                     motor vehicle emissions (129.33 tpy) to the total estimated NOX
                     annual anthropogenic emissions from all sources (1157.93 tpy) in the Libby PM2.5
                     nonattainment area is 11.17% of the total inventory. EPA indicated in its July 1, 2004 Transportation Conformity final rule (69 FR 40004) that mobile source emissions 
                    ( print page 55723)
                    of approximately 10% may be considered insignificant, but did not make 10% a specific threshold. While the 11.7% figure calculated for on-road NOX
                     in the Libby PM2.5
                     nonattainment area is slightly greater than this, in this same rulemaking EPA explained: “This example also illustrates the reason EPA believes it is important to have flexibility in implementing this provision. Although the commenter specifically mentions 10% as the threshold for finding motor vehicle emissions insignificant, EPA clarifies that this figure is a general guideline only. Depending on the circumstances, we may find that motor vehicle emissions that make up less than 10% of an area's total inventory are still significant. Conversely, we may also find that motor vehicle emissions in excess of 10% are still insignificant, under certain circumstances relating to the overall composition of the air quality situation. In general, the percentage of motor vehicle emissions in the area's total inventory is an important criterion for determining whether motor vehicles are a significant or insignificant contributor to an area's air quality problem, yet there are other criteria that EPA will examine when making this finding, as described in the regulatory text for § 93.109(k).” (69 FR 40062) [9] As stated in the 2004 preamble, 10 percent is a guideline only. As described below, EPA considered other factors that lead EPA to propose that motor vehicle emissions of NOX
                     are an insignificant regional contributor to the PM2.5
                     nonattainment problem. f. The Current State of Air Quality as Determined by Monitoring Data for PM2.5
                     NAAQS This factor is addressed with the ambient PM2.5
                     air quality data presented in section V.7.B above which demonstrate the Libby PM2.5
                     nonattainment area is attaining the PM2.5
                     annual NAAQS. Additional data, relevant to NOX
                     or in this case nitrates derived from NOX
                     emissions,[10]
                    
                     were provided by EPA with the 2009 final designations for the 24-hour 2006 PM2.5
                     NAAQS. This information, as provided in Table V.7-5 below, is from EPA's PM2.5
                     24-hour 2006 NAAQS final designations and is located at: 
                    *http://www.epa.gov/​ttn/​naaqs/​pm/​pm25_​2006_​techinfo.html.* Table V.7-5—PM2.5
                         Composition Data for Libby, MT
Area/County/State
PM2.5
                             composition data
Sulfate
                             
                                (μmg/m3
                                )
Nitrate
                             
                                (μmg/m3
                                )
Carbon
                             
                                (μmg/m3
                                )
Crustal
                             
                                (μmg/m3
                                )
Total
                             
                                (μmg/m3
                                )
Nitrate
                             percent
Carbon
                             percentLibby/Lincoln/MT
Total Concentration (Cold)
1.4
0.8
41.9
0.3
44.4
2
94Regional Concentration (Cold)
0.9
0.4
2.4
0.2
3.9
10
62Urban Concentration (Cold)
0.5
0.4
39.5
0.1
40.5
1
98Total Concentration (Warm)
1.2
0.0
6.7
0.8
8.7
0
77Regional Concentration  (Warm)
1.0
0.0
2.5
1.1
4.6
0
54Urban Concentration (Warm)
0.2
0.0
4.2
0.0
4.4
0
95Total Concentration (Annual Average)
1.0
0.1
12.8
0.4
14.3
1
90
 As can be seen in Table V.7-5 above, nitrates (as derived from NOX) are a very small component of the PM2.5
                     composition found in the Libby PM2.5
                     nonattainment area. Therefore, NOX
                     as derived from motor vehicle tailpipe emissions also is a very small component. This factor thus supports the proposed finding that on-road NOX
                     emissions are insignificant for the Libby PM2.5
                     nonattainment area. g. The Absence of SIP Motor Vehicle Control Measures for NOX As discussed in section V.7.C above, the Libby PM2.5
                     attainment plan took no credit for any emission reductions in the motor vehicle tailpipe and diesel exhaust categories (
                    *e.g.*
                     Federal tailpipe emission standards and fleet turnover). The State further described these assumptions in sections 27.12.7.3 (“Federal Tailpipe Standards Control Program”) and 27.12.11.4 (“PM2.5
                     2010 Demonstration of Compliance”) of the Libby attainment plan. EPA also notes there is no State or local mandated motor vehicle emission control requirements (e.g., inspection and maintenance program, fuels, or transportation control measures) for the Libby PM2.5
                     nonattainment area. Therefore this factor supports the proposed finding that on-road NOX
                     emissions are insignificant for the Libby PM2.5
                     nonattainment area. h. Historical Trends and Future Projections of the Growth of NOX
                     Motor Vehicle Emissions As noted in our discussion in section V.7.D above, the Libby attainment plan uses a 59% reduction in residential woodstove emissions to reach attainment of the annual PM2.5
                     NAAQS and took no credit for any emission reductions in the motor vehicle tailpipe and diesel exhaust categories. The State further described these assumptions in sections 27.12.7.3 (“Federal Tailpipe Standards Control Program”) and 27.12.11.4 (“PM2.5
                     2010 Demonstration of Compliance”) of the Libby attainment plan. EPA notes that the State used a conservative emission inventory approach for projecting the 2010 attainment year future growth which involved merely increasing the vehicle emissions by 2.1% (the population growth rate) from the 2005 base year inventory, and not taking any credit for potential emission reductions that may have been available from fleet turnover and the Federal tailpipe standards for vehicles. In addition, as we noted above, there are no State or local mandated motor vehicle emission control requirements (
                    *e.g.,*
                     inspection and maintenance program) for the Libby PM2.5
                     nonattainment area. This factor supports the proposed finding that on-road NOX
                     emissions are insignificant for the Libby PM2.5
                     nonattainment area. After weighing these four factors described in 40 CFR 93.109(m) and evaluated above, EPA proposes to find that on-road NOx emissions are insignificant for the Libby PM2.5
                     nonattainment area. i. Conclusion In view of our evaluation presented above per 40 CFR 93.109(m), EPA is proposing to find that direct PM2.5
                     and NOX
                     motor vehicle emissions are an insignificant contributor to the air quality issues associated with the PM2.5( print page 55724)
                    annual NAAQS in the Libby PM2.5
                     nonattainment area; thus, motor vehicle emission budgets for on-road direct PM2.5
                     and NOX
                     would not be established by this rulemaking. Based on our evaluation of the four factors described in 93.109(m), EPA proposes to conclude that it would be unreasonable to expect that the Libby PM2.5
                     nonattainment area would experience enough motor vehicle emissions growth such that a PM2.5
                     annual NAAQS violation would occur. VI. Proposed Action The EPA has reviewed Montana's SIP revision for attaining the 15μg/m3
                     annual PM2.5
                     NAAQS for the Libby PM2.5
                     nonattainment area. EPA is proposing to approve the State of Montana's revisions to the Lincoln County Air Pollution Control Program to be included in Montana's SIP, submitted on June 26, 2006, and the Libby PM2.5
                     attainment plan, submitted on March 26, 2008. Action was not taken earlier on the June 26, 2006, submittal at the request of the State of Montana to delay action until the submittal of the Libby PM2.5
                     attainment plan at a later date. EPA has determined that the SIP meets applicable requirements of the CAA, as described in the Clean Air Fine Particle Implementation Rule. Specifically, EPA has determined that Montana's SIP includes an attainment demonstration and adopted state regulations and programs needed to support the determination that the Libby PM2.5
                     nonattainment area will continue attaining the annual PM2.5
                     NAAQS. Finally, EPA is proposing to find on-road, directly emitted PM2.5
                     and NOX
                     in the Libby, Montana nonattainment area insignificant for regional transportation conformity purposes. VII. Statutory and Executive Order Reviews A. Executive Order 12866, Regulatory Planning and Review Under Executive Order 12866, (58 FR 51735 (October 4, 1993)) the Agency must determine whether the regulatory action is “significant” and therefore subject to the Office of Management and Budget (OMB) review and the requirements of the Executive Order. The Order defines “significant regulatory action” as one that is likely to result in a rule that may: (1) Have an annual effect on the economy of $100 million or more or adversely affect in a material way the economy, a sector of the economy, productivity, competition, jobs, the environment, public health or safety, or state, local, or tribal governments or communities; (2) create a serious inconsistency or otherwise interfere with an action taken or planned by another agency; (3) materially alter the budgetary impact of entitlements, grants, user fees, or loan programs or the rights and obligations of recipients thereof; or (4) raise novel legal or policy issues arising out of legal mandates, the President's priorities, or the principles set forth in the Executive Order.” The OMB has exempted this regulatory action from Executive Order 12866 review. B. Paperwork Reduction Act This action does not impose an information collection burden under the provisions of the Paperwork Reduction Act, 44 U.S.C. 3501 
                    *et seq.*
                     This action proposes to approve the SIP revisions submitted by the State of Montana. C. Regulatory Flexibility Act The Regulatory Flexibility Act (RFA) generally requires an agency to prepare a regulatory flexibility analysis of any rule subject to notice and comment rulemaking requirements under the Administrative Procedure Act or any other statute unless the agency certifies that the rule will not have a significant economic impact on a substantial number of small entities. Small entities include small businesses, small organizations, and small governmental jurisdictions. This proposed rule will not have a significant impact on a substantial number of small entities because SIP approvals and disapprovals under section 110 and subchapter I, part D of the Clean Air Act do not create any new requirements, but simply approve or disapprove requirements that the state is already imposing. Therefore because the Federal SIP approval does not create any new requirements, I certify that this action will not have a significant economic impact on a substantial number of small entities. Moreover, due to the nature of the Federal-state relationship under the Clean Air Act, preparation of flexibility analysis would constitute Federal inquiry into the economic reasonableness of state action. The Clean Air Act forbids EPA to base its actions concerning SIPs on such grounds. 
                    *Union Electric Co.,*
                     v.
                    *U.S. EPA,*
                     427 U.S. 246, 255-66 (1976); 42 U.S.C. 7410(a)(2). D. Unfunded Mandates Reform Act Title II of the Unfunded Mandates Reform Act of 1995 (UMRA), Public Law 104-4, establishes requirements for Federal agencies to assess the effects of their regulatory actions on state, local, and tribal governments and the private sector. Under section 202 of the UMRA, EPA generally must prepare a written statement, including a cost-benefit analysis, for proposed and final rules with “Federal mandates” that may result in expenditures to state, local, and tribal governments, in the aggregate, or to the private sector, of $100 million or more in any one year. Before promulgating an EPA rule for which a written statement is needed, section 205 of the UMRA generally requires EPA to identify and consider a reasonable number of regulatory alternatives and adopt the least costly, most cost-effective or least burdensome alternative that achieves the objectives of the rule. The provisions of section 205 do not apply when they are inconsistent with applicable law. Moreover, section 205 allows EPA to adopt an alternative other than the least costly, most cost-effective or least burdensome alternative if the Administrator publishes with the final rule an explanation why that alternative was not adopted. Before EPA establishes any regulatory requirements that may significantly or uniquely affect small governments, including tribal governments, it must have developed under section 203 of the UMRA a small government agency plan. The plan must provide for notifying potentially affected small governments, enabling officials of affected small governments to have meaningful and timely input in the development of EPA regulatory proposals with significant Federal intergovernmental mandates, and informing, educating, and advising small governments on compliance with the regulatory requirements. EPA has determined that this rule does not contain a Federal mandate that may result in expenditures of $100 million or more for state, local, and tribal governments, in the aggregate, or the private sector in any one year. This Federal action proposes to partially approve and partially disapprove pre-existing requirements under state or local law, and to disapprove a redesignation request, and imposes no new requirements. Accordingly, no additional costs to state, local, or tribal governments, or to the private sector, result from this action. Thus, today's rule is not subject to the requirements of sections 202 and 205 of the UMRA. E. Executive Order 13132, Federalism Executive Order 13132, entitled “Federalism” (64 FR 43255, August 10, 1999), requires EPA to develop an accountable process to ensure “meaningful and timely input by state and local officials in the development of regulatory policies that have federalism implications.” “Policies that have federalism implications” is defined in 
                    ( print page 55725)
                    the Executive Order to include regulations that have “substantial direct effects on the states, on the relationship between the national government and the states, or on the distribution of power and responsibilities among the various levels of government.” This proposed rule does not have federalism implications. It will not have substantial direct effects on the states, on the relationship between the national government and the states, or on the distribution of power and responsibilities among the various levels of government, as specified in Executive Order 13132. This rule merely proposes to partially approve and partially disapprove state rules implementing a Federal standard, and to disapprove a redesignation request, and does not alter the relationship or the distribution of power and responsibilities established in the Clean Air Act. Thus, Executive Order 13132 does not apply to this rule. F. Executive Order 13175, Coordination With Indian Tribal Governments Executive Order 13175, entitled Consultation and Coordination With Indian Tribal Governments (65 FR 67249, November 9, 2000), requires EPA to develop an accountable process to ensure meaningful and timely input by tribal officials in the development of regulatory policies that have tribal implications. This proposed rule does not have tribal implications, as specified in Executive Order 13175. It will not have substantial direct effects on tribal governments, on the relationship between the Federal government and Indian tribes, or on the distribution of power and responsibilities between the Federal government and Indian tribes. This action does not involve or impose any requirements that affect Indian Tribes. Thus, Executive Order 13175 does not apply to this rule. G. Executive Order 13045, Protection of Children From Environmental Health Risks and Safety Risks *Protection of Children From Environmental Health Risks and Safety Risks*
                     (62 FR 19885, April 23, 1997), applies to any rule that: (1) Is determined to be economically significant as defined under Executive Order 12866, and (2) concerns an environmental health or safety risk that EPA has reason to believe may have a disproportionate effect on children. If the regulatory action meets both criteria, the Agency must evaluate the environmental health or safety effects of the planned rule on children, and explain why the planned regulation is preferable to other potentially effective and reasonably feasible alternatives considered by the Agency. EPA interprets Executive Order 13045 as applying only to those regulatory actions that are based on health or safety risks, such that the analysis required under section 5-501 of the Order has the potential to influence the regulation. This proposed rule is not subject to Executive Order 13045 because it proposes to approve a state rule implementing a Federal program. H. Executive Order 13211, Actions That Significantly Affect Energy Supply, Distribution, or Use This rule is not subject to Executive Order 13211, Actions Concerning Regulations That Significantly Affect Energy Supply, Distribution, or Use (66 FR 28355, May 22, 2001) because it is not a significant regulatory action under Executive Order 12866. I. National Technology Transfer and Advancement Act Section 12(d) of the National Technology Transfer and Advancement Act of 1995 (“NTTAA”), Public Law 104-113, section 12(d) (15 U.S.C. 272 note) directs EPA to use voluntary consensus standards in its regulatory activities unless to do so would be inconsistent with applicable law or otherwise impractical. Voluntary consensus standards are technical standards (e.g., materials specifications, test methods, sampling procedures, and business practices) that are developed or adopted by voluntary consensus standards bodies. The NTTAA directs EPA to provide Congress, through OMB, explanations when the Agency decides not to use available and applicable voluntary consensus standards. This proposed rulemaking does not involve technical standards. Therefore, EPA is not considering the use of any voluntary consensus standards. List of Subjects in 40 CFR Part 52 Environmental protection
Air pollution control
Intergovernmental relations
Oxides of nitrogen
Particulate matter
Reporting and recordkeeping requirements
 Authority:
                    42 U.S.C. 7401 
                        *et seq.* Dated: September 2, 2010. Stephen S. Tuber, Acting Regional Administrator, Region 8.


# Footnotes

1.
    
                         Subpart 1 applies to nonattainment areas generally. Back to Citation
 2.
    
                         The boundaries of the District are identical to those for the nonattainment area. Back to Citation
 3.
    
                         Ward, T.J., Rinehart, L.R., Lange, T. The 2003/2004 Libby, Montana PM2.5
                         Source Apportionment Research Study. Aerosol Science and Technology. Vol. 40:166-177. 2006. Back to Citation
 4.
    
                         Ibid. Back to Citation
 5.
    
                         The 2005 NEI data from EPA's PM2.5
                         24-hour 2006 NAAQS final designations information are available at: 
                        *http://www.epa.gov/​ttn/​naaqs/​pm/​pm25_​2006_​techinfo.html.* Back to Citation
 6.
    
                         
                        *See http://www.epa.gov/​ttn/​naaqs/​pm/​pm25_​2006_​techinfo.html;*
                         Factor 4.B “Vehicle Miles Traveled”. Back to Citation
 7.
    
                         VMT data was communicated in a February 26, 2010, email from Jim Carlin of MTDEQ to Tim Russ of EPA Region 8. Back to Citation
 8.
    
                         The “Fires” category of the 2005 NEI relates to wildfires, prescribed burns and such. This correlates to the “Large Prescribed Burning” and “General Burning” categories in the State's Table 5.1A. Back to Citation
 9.
    
                         EPA redesignated the insignificance provision of the transportation conformity rule from 40 CFR 93.109(k) to 40 CFR 93.109(m) in its March 24, 2010 “PM Amendments” final rule (75 FR 14260). Back to Citation
 10.
    
                         Nitrogen oxides react in the atmosphere to form nitrates. For our purposes, the impact of NOX
                         emissions is measured as the amount of nitrates found at the PM2.5
                         monitor. Back to Citation


[FR Doc. 2010-22848 Filed 9-13-10; 8:45 am] BILLING CODE 6560-50-P