Page 1 of 36

From: Lydia Wegman/RTP/USEPA/US To: nfrey@omb.eop.gov Cc: Richard Wayland/RTP/USEPA/US@EPA, James Hemby/RTP/USEPA/US@EPA, Tim

Hanley/RTP/USEPA/US@EPA, Lewis Weinstock/RTP/USEPA/US@EPA, Joseph - J Dougherty/DC/USEPA/US@EPA, Beth Hassett - Sipple/RTP/USEPA/US@EPA, martin.karen@epa.gov Date: 06/11/2012 01:44 PM Subject: Revisions to the Monitoring Section of the PM NAAQS preamble Nathan, Attached is our redline version of the monitoring section (section VIII) of the PM NAAQS preamble in response to interagency comments we have received both verbally and in writing. Tim Hanley has provided a brief overview of the changes we have made. Please let me know if you have any questions. Thanks. Here is the brief summary of the changes: 1. Clarifying the applicability of micro - and middle - scale monitoring sites to the an nual PM 2.5 NAAQS (on pages 9 - 12). 2. Proposed Addition of a Near - road Component to the PM 2.5 Monitoring Network In this section we added more information on the monitoring objectives and value of adding these sites. (Page 13) 3. Some revised wording o n the connection of data from the near - roadway sites to PSD and conformity. (Page 14) 4. Identification of when the near - road data will be available (2018) (Page 17)Page 2 of 36

VIII. Proposed Amendments to Ambient Monitoring and Reporting Requirements The EPA proposes changes to the ambient air monitoring, reporting, and network design requirements associated with the PM NAAQS . Ambient PM monitoring data are used to meet a variety of monitoring objectives including determining whether an area is in violation of the PM NAAQS . Ambient PM monitoring data are collected by state, local, and tribal monitoring agencies (“monit oring agencies”) in accordance with the monitoring requirements contained in 40 CFR parts 50, 53, and 58 . This section discusses the monitoring changes that the EPA is proposing to support the proposed PM NAAQS summarized in sections II I .F, I V .F, and V I .F above . A. Issues Related to 40 CFR Part 53 (Reference and Equivalent Methods) To be used in a determination of compliance with the PM NAAQS, PM data are typically collected using samplers or monitors employing an FRM or FEM . The EPA also allows use of alterna tive methods where explicitly stated in the monitoring methodology requirements (appendix C of 40 CFR part 58), such as PM 2.5 ARMs which can be used to determine compliance with the NAAQS . The EPA prescribes testing and approval criteria for FRM and FEM me thods in 40 CFR part 53. 1. PM 2.5 and PM 10
- 2.5 Federal Equivalent Methods In 2006, the EPA finalized new testing and performance criteria for Class II and Class III FEMs (71 FR 61281 to 61289, October 17, 2006) . Class II methods are equivalent methods for P M 2.5 or PM 10
- 2.5 that utilize a PM 2.5 sampler or PM 10
- 2.5 sampler in which integrated PM 2.5 samples or PM 10
- 2.5 samples are obtained from the atmosphere by filtration and are then subjected to a filter conditioning process followed by gravimetric mass dete rmination . Class II equivalent methods are different from Class I equivalent methods because of substantial deviations from the design specifications of the sampler specified for reference methods in appendix L or appendix O (as applicable) of 40 CFR part 50 . Class III refers to those methods for PM 2.5 or PM 10
- 2.5 that are employed to provide PM 2.5 or PM 10
- 2.5 ambient air measurements representative of one
- hour or less integrated PM 2.5 or PM 10
- 2.5 concentrations, as well as 24
- hour measurements determined as, or equivalent to, the mean of 24 one
- hour consecutivePage 3 of 36

measurements . These new testing and performance criteria were developed by the EPA and reviewed through consultation with the CASAC AAMMS 1 and then through proposal (71 FR 2710 to 2808, January 17, 2006) and final rulemaking in 2006 (71 FR 61236 to 61328, October 17, 2006) . The performance criteria were designed to ensure enough stringency in testing that subsequently deployed monitors would provide data of expected quality (i.e., they would meet the data quality objectives), but not so stringent that instrument manufacturers would be discouraged from testing their instrument and seeking approval as a Class II or III equivalent method . At the time of this proposal, the EPA has approved two PM 10
- 2.5 Class II manual methods, one Class III PM 10
- 2.5 continuous method, and six Class III PM 2.5 continuous methods. 2 While the EPA has approved these PM 2.5 Class III continuous FEMs, only two of those m ethods are deployed on a wide
- enough basis across the country to support initial analyses of data quality and comparability to collocated FRM samplers . The Policy Assessment discusses an analysis of the quality of data from these two FEMs (US EPA, 2011a, p . 4
- 50) . This initial analysis found that some sites with continuous PM 2.5 FEMs have an acceptable degree of comparability with collocated FRMs, while others had less acceptable data comparability that would not meet the performance criteria used to approv e the FEMs. The EPA continues to believe that an effective PM 2.5 monitoring strategy includes the use of both filter
- based FRM samplers and well
- performing continuous PM 2.5 monitors . Well
- performing continuous PM 2.5 monitors would include both non
- approved continuous PM 2.5 monitors and approved Class III continuous FEMs that meet the performance criteria described in table C
- 4 of 40 CFR part 53 when comparing to a collocated FRM operated by the monitoring agency . The use of Class III continuous FEMs at SLAM S is described in more detail in section VII I . B. 3.b.ii below . Monitoring 1 The EPA consulted with the CASAC AAMMS on several PM monitoring topics in a public meeting on September 21 and 22, 2005 . Materials from this meeting can be found on EPA’s website at: http://www.epa.gov/ttn/amtic/casacinf.html . 2 A list of designated Reference and Equivalent methods is available on EPA’s website at: http://www.epa.gov/ttn/amtic/criteria.html .Page 4 of 36

agencies are encouraged to evaluate the quality of data being generated by FEMs and, where appropriate, reduce the use of manual, filter
- based samplers to improve operational efficien cy and lower overall operating costs . To encourage such a strategy, the EPA is working with numerous stakeholders including the monitoring committee of NACAA, instrument manufacturers, and monitoring agencies to support national data analyses of continuous PM 2.5 FEM performance, and where such performance does not meet data quality objectives, to develop and institute a program of best practices to improve the quality and consistency of resulting data. The EPA believes that progress is being made to implement well performing PM 2.5 continuous FEMs across the nation . As noted earlier, the first few steps involved the EPA developing and approving the testing and performance criteria which were finalized in 2006, followed by instrument companies performin g field testing and submitting applications to the EPA, and EPA review and approval, as appropriate, of Class III FEMs . In the current step, monitoring agencies are testing and assessing the data comparability from continuous PM 2.5 FEMs . While some agencie s are achieving acceptable data comparability and others are not, the EPA wants to ensure that all monitoring agencies have the appropriate information to maximize data quality from their PM 2.5 continuous FEMs before considering any changes to regulatory t esting requirements intended to demonstrate equivalency of candidate Class III FEMs . Since we are still early in the process of learning the data comparability between approved PM 2.5 continuous methods and collocated FRMs (assessments across the country ar e only available for two of the six methods), and some of the agencies operating those methods are achieving acceptable data comparability, the EPA does not believe it is appropriate at this time to propose any modifications to either the performance or te sting criteria in 40 CFR part 53 used to approve PM 2.5 continuous FEMs. While EPA is not proposing any changes to the performance or testing criteria in 40 CFR part 53 used to approve PM 2.5 continuous FEMs, the EPA proposes an administrative change to p ar t 53.9

– “Conditions of designations.” This section describes a number of conditions that must be met by a manufacturer as a condition of maintaining designation of an FRM or FEM . Subsection (c) of thisPage 5 of 36

section reads , “ Any analyzer, PM 10 sampler, PM 2.5 sam pler, or PM 10
- 2.5 sampler offered for sale as part of a FRM or FEM shall function within the limits of the performance specifications referred to in 40 CFR 53.20(a), 53.30(a), 53.50, or 53.60, as applicable, for at least 1 year after delivery and acceptanc e when maintained and operated in accordance with the manual referred to in 40 CFR 53.4(b)(3).” The EPA’s intent in this requirement is to ensure that methods work within performance criteria, which includes methods for PM 2.5 and PM 10
- 2.5 ; however, there i s no specific reference to performance criteria for Class II and III PM 2.5 and PM 10
- 2.5 methods . Therefore, the EPA proposes to link the performance criteria referred to in 40 CFR part 53.35 associated with Class II and III PM 2.5 and PM 10
- 2.5 methods with this requirement for maintaining designation of approved FEMs . The specific performance criteria identified in 40 CFR 53.35 for PM 2.5 and PM 10
- 2.5 methods are available in table C
- 4 to subpart C of 40 CFR part 53 . 2. Use of CSN Methods to Suppo rt the Proposed New Secondary PM 2.5 Visibility I ndex NAAQS The EPA, monitoring agencies, and external scientists and policy makers use PM 2.5 data from the CSN to support several important monitoring objectives such as: development of modeling tools and the application of source apportionment modeling for control strategy development to implement the NAAQS; health effects and exposure research studies; assessment of the effectiveness of emission reductions strategies through the characterization of air quali ty; and development of SIPs . The initial CSN began with a pilot of 13 sites in 2000 and grew rapidly over the next two years . Since 2006, the size of the CSN has remained relatively stable at approximately 200 stations. The methods employed in the CSN are well documented and uniformly implemented across the country . However, between May 2007 and October 2009, the CSN transitioned to a new method of sampling and analyses for carbon that is consistent with the IMPROVE network methodology. 3 The
3 In the IMPROVE program, artifact adjusted OC (i.e. , PM 2.5 OC) is simply reported as OC . That is the value used to produce OM for haze calculations . For th e CSN measurements, the OC artifact needed to convert measured OC into PM 2.5 OC is estimated from sampler
- specific network
- wide field blanks ( Frank, 201 2 ).Page 6 of 36

CSN measuremen ts have a strong history of being reviewed by CASAC technical committees, both during their initial deployment about ten years ago, and during the more recent transition to carbon sampling that is consistent with the IMPROVE protocols (Henderson, 2005c) . T he CSN network is described in the Policy Assessment (US EPA, 2011a, Appendix B, section B.1.3). As noted in section V I .D.1.c above, the proposed new secondary standard for PM 2.5 to address PM
- related visibility impairment is defined in terms of a PM 2.5 visibility index, which would use PM 2.5 speciation measurement data . The EPA proposes that measurements using either the CSN or IMPROVE methods 4 be eligible for use to calculate PM 2.5 visibility index values . The EPA believes this proposed approach is app ropriate because the methods for CSN and IMPROVE are well documented 5 in nationally implemented Quality Assurance Project Plans (QAPPs) and accompanying Standard Operating Procedures (SOPs) are validated through independent performance testing, and because numerous state, local, and tribal agencies are already experienced in the use of these methods. With reference to CSN methods, the EPA is specifically not proposing to include testing or performance criteria for approval of CSN measurements as FRMs. The EPA believes that the proposed framework of using the current, well
- documented set of CSN and IMPROVE methods provides a nationally consistent way to provide the chemical species data used in calculating PM 2.5 visibility index values, while preserving the flexibility for timely improvements to methods for measuring chemical species. Monitoring programs wishing to establish methods for chemical speciation in support of the proposed PM 2.5 visibility index would do so by following the methods and SOPs publical ly available on both the IMPROVE or the EPA (for CSN) websites. 6 The EPA solicits comment on this approach to

4 Appendix C to 40 CFR part 58

– Ambient Air Quality Monitoring Methodology is where EPA specifies the criteria pollutant monitoring methods which must be used at SLAMS and NCore, which are a subset of SLAMS. 5 CSN documents are available at: http://www.epa.gov/ttn/amtic/speciepg.html ; IMPROVE documents are available at: http://vista.cira.colostate.edu/improve/Data/QA_QC/qa_qc_Branch.htm ) . 6 SOP’s for the CSN pro gram are available in Docket number EPA
- HQ
- OAR
- 2007
- 0492 and on EPA’s website at: http://www.epa.gov/ttn/amtic/specsop.html . SOP’s for the IMPROVE program are availablePage 7 of 36

include the CSN and IMPROVE measurements by reference and not require that such methods be approved as FRMs. As discussed in section VI I .A.5 above, the calculation of the PM 2.5 visibility index values would use historic monthly average relative humidity data based on a ten
- year climatological data base. This data base would be based on measurements of relative humidity reported through NOAA at routine weather stations and not relative humidity measurements specific to the SLAMS stations. B. Proposed Changes to 40 CFR Part 58 (Ambient Air Quality Surveillance) 1. Proposed Terminology Changes The EPA proposes to revise several terms associated with PM 2 .5 monitor placement to ensure consistency with other NAAQS and to conform with long
- standing practices in siting of equipment by monitoring agencies. The EPA proposes to revoke the term “community
- oriented” and replace it with the term “area
wide.” The t erm “community
- oriented,” while used within the description of the design criteria for PM 2.5 , is not defined and has not been used in the design criteria for other NAAQS pollutants . Appendix D to 40 CFR part 58 presents a functional usage of the term where sites at the neighborhood and urban scale area are considered to be “community
- oriented.” In addition, population
- oriented , micro
- or middle
- scale PM 2.5 monitoring may also be considered “community
- oriented” when determined by the Regional Administrator to represent many such locations throughout a metropolitan area . The EPA proposes to replace this functional usage of “community
- oriented” with the term “area
- wide” in the text of the PM 2.5 network design criteria and to define it in 40 CFR 58.1 to provide a more consistent usage of this concept throughout appendix D of 40 CFR part 58 . The EPA proposes that the terminology would read

– “Area
- wide means all monitors sited at neighborhood, urban, and regional scales, as well as those monitors sited at either mi cro - or middle
- scale that are representative of many such locations in in Docket number EPA
- HQ
- OAR
- 200 7
- 0492 and on the IMPROVE website at: http://vista.cira.colostate.edu/improve/publications/IMPROVE_SOPs.htm .Page 8 of 36

the same CBSA.” The EPA proposes to revoke the term “Community Monitoring Zone” (CMZ) and references to it in 40 CFR part 58 . Community monitoring zone is currently defined as “an option al averaging area with established, well defined boundaries, such as county or census block, within an MPA that has relatively uniform concentrations of annual PM 2.5 as defined by appendix N of 40 CFR part 50 of this chapter . Two or more community oriented state and local air monitoring stations (SLAMS) monitors within a CMZ that meet certain requirements as set forth in appendix N of 40 CFR part 50 may be averaged for making comparisons to the annual PM 2.5 NAAQS.” The EPA proposes to revoke this term and r eferences to it since, as discussed in section VI I . A .2 above, the EPA is proposing to eliminate all references to the spatial averaging option throughout appendix N. 2. Special Considerations for Comparability of PM 2.5 Ambient Air Monitoring Data to the NAAQS In general, ambient monitors must meet a basic set of requirements before the resulting data can be used for comparison to the NAAQS; these requirements include the presence and implementation of an approved quality assurance project plan, the use of meth ods that are reference, equivalent, or other approved method as described in appendix C to 40 CFR part 58, and compliance with the probe and siting path criteria as described in appendix E to 40 CFR part 58 . While these 40 CFR part 58 requirements apply to a monitor that provides data for comparison to the NAAQS, only in the PM 2.5 monitoring requirements are additional restrictions prescribed within the monitoring rules. 7 These additional restrictions provide that sites must be “population
- oriented” for com parison to either the 24
- hour or annual NAAQS, and specifically for comparison to the annual NAAQS, sites must additionally be sited to represent area
- wide locations . There is a related provision that provides for comparing sites at smaller scales to the annual NAAQS when the (micro
- or middle
- scale) site collectively identifies a larger region of localized high ambient PM 2.5 concentration . The inclusion of these provisions in the PM 2.5 monitoring requirements since the 1997 7 These are referenced in 40 CFR 58.30 (Special considerations for data comparisons to the NAAQS) .Page 9 of 36

promulgation of the PM 2.5 NAAQ S and associated monitoring requirements has resulted in substantial ambiguity when the EPA and state, local, and tribal agencies consider the design of PM 2.5 monitoring networks as NAAQS are revised as well as how unmonitored locations should be treated i n modeling exercises. 8 Accordingly, the EPA proposes to revise these particular PM 2.5 requirements for consistency with long
- standing practices in all other NAAQS pollutant monitoring networks, and to ensure interpretation of the monitoring rules does not cause ambiguity in considering treatment of unmonitored areas . Each of these topics and our proposal to revoke or modify the requirements is described below. a. Revoking Use of Population
- Oriented as a Condition for Comparability of PM 2.5 Monitoring Sites to the NAAQS The EPA proposes to revoke the requirement that PM 2.5 monitoring sites be “population
oriented” for comparison to the NAAQS . This requirement is inconsistent with our definition of ambient air which the NAAQS employ . The EPA’s definition of ambie nt air is specified in 40 CFR 50.1

–
“ Ambient air means that portion of the atmosphere, external to buildings, to which the general public has access.” The EPA’s definition of “population
- oriented” is provided in 40 CFR 58.1
- “ Population
oriented monitori ng (or sites) means residential areas, commercial areas, recreational areas, industrial areas where workers from more than one company are located, and other areas where a substantial number of people may spend a significant fraction of their day.” The EPA ’s intention in proposing to revoke the requirement that PM 2.5 monitoring sites be “population
- oriented” for comparison to the NAAQS is to ensure that the monitoring rules do not create an ambiguity in the use of data by having a different definition from the definition of ambient air in 40 CFR 50.1 itself . Also, EPA’s proposal to revoke this term in no way changes the requirements in the PM 2.5 network design criteria, which will continue to focus on sites representing “area
- wide” locations; thus continuing to represent locations with population exposure . While the use of the term “population
- oriented” has little effect on how data from existing sites are treated (as explained below there are no remaining sites designated as not being 8 Modeling can be associated with either PSD or transportation conformity as discussed in sections I X .F and I X .G , respectively, below.Page 10 of 36

“population
- oriented”), the inclusion of this requirement in the monitoring rules creates substantial ambiguity in how to treat potential locations of exposure such as in applying modeling across an area . By reverting to the long
- standing definition of ambient air, the EPA will be able to more clearly define how to treat potential exposure receptors, regardless of whether monitoring exists or not . In reviewing the impact that this proposed change might have on the nation’s PM 2.5 monitoring network, the EPA notes that there are n o remaining sites operating affirmatively as “no n population
oriented.” The last known non population
- oriented site at Sun Metro in El Paso Texas (AQS ID: 48
- 141
- 0053), was shut down in October 2010 and is in the process of being moved to a nearby neighborhood . While a monitoring agency could still set u p a new site in any area, including one in an area that does not meet the definition of population
- oriented, which the EPA is proposing to revoke, there are other monitoring options that may provide more useful information and still result in data that are not comparable to the NAAQS; for instance, using a chemical speciation network sampler that provides chemical species information or continuous PM 2.5 monitor that provides high time
- resolution data, but is not approved as an FEM . Even if a monitoring agen cy wanted to use an FRM, an agency could still operate a monitor for up to 24 months as a n SPM without any risk of data being used for comparison to the NAAQS. b. Applicability of Micro
- and Middle
- scale Monitoring Sites to the Annual PM 2.5 NAAQS The EPA is clarifying language used to determine when proposes that PM 2.5 monitoring sites at micro
- and middle
- scale locations are be comparable to the annual NAAQS . , unless the monitoring site has been approved by the Regional Administrator as a “relatively unique micro
- scale or localized hot
spot, or unique middle
- scale site . ” 9 The EPA’s regulations already provide that sites at micro
- and middle
- scale locations are eligible for comparison to the 24 hour NAAQS (40 CFR 58.30) . The EPA’s
9 The term “relatively unique micro
- scale or localized hot
- spot, or unique middle s cale site” is consistent with the terminology already presented in 40 CFR 58.30

– Special considerations for data comparisons to the NAAQS, with the exception that the EPA is proposing to remove references to “population
oriented” as described in section VII I .B.2.a .Page 11 of 36

existing monitoring language (40 CFR part 58, appendix D, section 4.7) attempts to explain how to treat micro
- and middle
- scale sites with consideration of two factors when determining applicability of the annual NAAQS to these sites . One factor is based on whether the site is considered “unique.” The second and somewhat related factor is based on whether there are many similar locations. The EPA’s current rules, as specified in 40 CFR 58.30, state that “PM 2.5 data that are representative, not of area
- wide but rath er, of relatively unique population
- oriented micro
- scale, or localized hot spot, or unique population
- oriented middle
- scale impact sites are only eligible for comparison to the 24
- hour PM 2.5 NAAQS . For example, if the PM 2.5 monitoring site is adjacent to a unique dominating local PM 2.5 source or can be shown to have average 24
- hour concentrations representative of a smaller than neighborhood spatial scale, then data from a monitor at the site would only be eligible for comparison to the 24
- hour PM 2.5 NAAQS. ” The EPA is clarifying proposes to add language to that explicitly state s that measuring PM 2.5 in micro
- and middle
- scale environments near emissions of mobile sources, such as a highway, does not constitute being impacted by a “unique” source . Mobile sources are rather ubiquitous and, as such, there are many locations throughout an urban area where elevated exposures could occur . Therefore, any potential location for a PM 2.5 monitoring site, even micro
- and middle
- scale sites near roadways would be eli gible for comparison to the annual NAAQS . The EPA’s existing definition of middle
- scale for PM 2.5, as specified in appendix D to 40 CFR part 58, already states, “(2) Middle scale

— People moving through downtown areas, or living near major roadways, encounte r particle concentrations that would be adequately characterized by this spatial scale . Thus, measurements of this type would be appropriate for the evaluation of possible short
- term exposure public health effects of particulate matter pollution . In many s ituations, monitoring sites that are representative of micro
- or middle
- scale impacts are not unique and are representative of many similar situations . This can occur along traffic cor ridors or other locations in a r esidential district . In this case, one l ocation is representative of a number of small scale sites and is appropriate for evaluation of long
- term or chronic effects . This scale also includes the characteristic concentrations for other areas with dimensions of a Formatted: Indent: First line: 0"Page 12 of 36

few hundred meters such as the par king lot and feeder streets associated with shopping centers, stadia, and office buildings.” With the reference to “traffic corridors” and related text, the EPA emphasizes that this type of location, which is referred to as near
- road, should not be conside red “unique.” The second and related factor is whether the location should be considered a unique “hot
- spot” or if there are lots of other similar locations located throughout the area . Unique “hot
- spot” locations would continue to be eligible only for com parison to the 24
- hour NAAQS, as they would not be considered to represent area
- wide concentrations . In the cases where there are lots of other similar locations throughout the same area, the EPA affirmatively considers that to be an “area
- wide” location; therefore, this type of site would be eligible for comparison to both the annual and 24
- hour PM 2.5 NAAQS. The practical effect of this proposed change is that under the existing monitoring requirements, sites in micro
- or middle
- scale locations require Regional Administrator approval for comparison to the annual PM 2.5 NAAQS, while with the proposed change the Regional Administrator would be responsible for approving sites that are “unique” micro
- or middle
- scale locations and therefore not comparable to the PM 2.5 annual NAAQS. Since t he EPA and monitoring agencies already have a process for approving PM 2.5 monitoring sites as described in the Annual Monitoring Network Plan due to the applicable each EPA Regional Office by July 1 of each year (described in 40 CFR 58.10) . This existing process provides for identification of sites that are su i table and sites that are n o t suitable for comparison against the annual PM 2.5 NAAQS ( §58.10 (b)(7)) . This clarifying language will provide consistency between the PM 2.5 design criteria described in appendix D to 40 CFR part 58 and the example provided in the special consi de rations for data comparisons to the NA AQS network design (§58.30) . Therefore, this clarifying language will help to ensure a more consistent identification and approval of sites in annual monito r ing network plans that are or are not suitable for comparison to the annual NAAQS. , there is no additional burden on the states or the EPA to review and approve sites as a result of this proposed chan ge . The EPA proposes to align Formatted: Font: 12 pt Formatted: Normal, No bullets or numberingPage 13 of 36

existing language cited in the definition of middle
- scale for PM 2.5 with the language cited in 40 CFR 58.30 (“Special considerations for data comparisons to the NAAQS”). 3. Proposed Changes to Monitoring for the National Ambient Air Monitoring System a. Background As described in appendix D to 40 CFR part 58, the ambient air monitoring networks must be designed to meet three basic monitoring objectives: (a) Provide air pollution data to the general public in a timely manner . Data can be presented to the public in a number of attractive ways including through air quality maps, newspapers, Internet sites, and as part of weather forecasts and public advisories . (b) Support compliance with ambient air quality standards and emissions strat egy development . Data from FRM, FEM, and ARM monitors for NAAQS pollutants will be used for comparing an area’s air pollution levels against the NAAQS . Data from monitors of various types can be used in the development of attainment and maintenance plans . SLAMS, and especially National Core Monitoring Network (NCore) 10 station data, will be used to evaluate the regional air quality models used in developing emission strategies and to track trends in air pollution abatement control measures’ impact on improvi ng air quality . In monitoring locations near major air pollution sources, source
- oriented monitoring data can provide insight into how well industrial sources are controlling their pollutant emissions . (c) Support for air pollution research studies . Air po llution data from the NCore network can be used to supplement data collected by researchers working on health effects assessments and atmospheric processes or for monitoring methods development work. To support the air quality management work indicated in the three basic air monitoring objectives, a network must be designed with a variety of types of monitoring sites . Monitoring sites must be capable of informing managers about many things including the peak air pollution levels, typical levels in populate d areas, air pollution transported into and outside of a city or region, and air pollution 10 NCore is a multi
- pollutant network that integrates several advanced measurements for particles, gases and meteorology (US EPA, 2011a, Appendix B, section B.4) . Measurements required at NCore include PM 2.5 mass and speciation, PM 10
- 2.5 mass, ozone, CO , SO 2 , NO, NO y , and basic meteorology.Page 14 of 36

levels near specific sources . To summarize some of these sites, here is a listing of six general site types: (a) sites located to determine the highest concentration s expected to occur in the area covered by the network; (b) sites located to measure typical concentrations in areas of high population density; (c) sites located to determine the impact of significant sources or source categories on air quality; (d) sites located to determine general background concentration levels; and (e) sites located to determine the extent of regional pollutant transport among populated areas; and in support of secondary standards. b. Primary PM 2.5 NAAQS In this section, the EPA proposes to add a near
- road component to the PM 2.5 network design criteria and to clarify the use of approved PM 2.5 continuous FEMs at SLAMS. i. Proposed Addition of a Near
- road Component to the PM 2.5 Monitoring Network The EPA believes that there are gradients in near - roadway PM 2.5 that are most likely to be associated with heavily travelled roads, particularly those with significant heavy
- duty diesel activity, with the largest numbers of impacted populations in the largest CBSAs in the country (Ntziachristos et al . , 2007; Ross et al., 2007; Yanosky et al . , 2008; Zwack et al . , 2011) . To better understand the potential health impacts of these exposures , t he EPA proposes to add a near
- road component to the compliance network design for PM 2.5 monitoring . The EPA believ es that by adding a modest number of PM 2.5 monitoring sites that are leveraged with measurements of other pollutants in the near
- road environment, a number of key monitoring objectives will be supported, including the collection of NAAQS comparable data wh ich would support public health protection for people living in the near
- road environment , support for long
- term hea l th studies investigating adverse effects on people , providing a better understanding of pollutant gradients impact ing neighborhoods that parallel major roads, availability of data to validate performance of models simulating near
- road dispersion, the characterization of areas with potentially elevated concentrations and/or poor air quality , the implementation of a multi
- pollutant paradigm as stated in the NO 2 NAAQS proposed rule (74 FR 34442, July 15, 2009) , and monitoring goals consistent with existing objectives noted in the specific designPage 15 of 36

criteria for PM 2.5 described in appendix D, 4.7.1(b) to 40 CFR part 58 . Near
- roa d PM 2.5 sites would also make measurement data available for complex lo cations not routinely monitor ed currently that may be valuable for the help to eliminate confusion over applica ble receptor locations in implementation of PSD/ new source review ( NSR ) the Agency’s permitting program and t T ransportation c C onformity determinitation s PM Hot
- Spot guidance by physically requiring monitoring in locations that historically were generally modeled but not monitored . The monitoring methods that are appropriate f or this purpose are an FRM, FEM, or ARM . The EPA recognizes that there are limitations in the ability of some of these PM methods to accurately measure PM 2.5 mass due to the incomplete retention of semi
- volatile material on the sampling medium (US EPA , 2009a, section 3.4.1 .1) . This limitation is relevant to the near
- road environment as well as to other environments where PM is expected to have semi
- volatile components . The EPA also recognizes that continuous PM 2.5 FEMs, which provide mass concentration data on an hourly basis, are better suited to accomplish the goals of near
- road monitoring as they will complement the time resolution of the other air quality measurements and traffic data collected at the same sites . In this regard, particular PM 2.5 FEMs are better suited for near
- road monitoring than FRMs . However, filter
- based FRMs do offer some advantages which may be highly desirable for near
- road monitoring, such as readily available filters for later chemical analysis such as for elemental compositi on by x
- ray fluorescence and BC by transmissometry . As a result of these tradeoffs, monitoring agencies are encouraged to select one or more PM 2.5 methods for deployment at near

– road monitoring stations that best meet their agencies monitoring objectives w hile ensuring that at least one of those methods is appropriate for comparison to the NAAQS (i.e., a FRM, FEM, or ARM) . Additionally, the EPA recognizes that the near
- road sites would provide a valuable platform for evaluating emerging monitoring technolo gies and for measuring other pollutants besides PM 2.5 mass to enhance knowledge of exposure in the near road environment and to support the characterization and comparison of specific method readings in an emission
- rich environment . Further, i n its respons e to thePage 16 of 36

EPA on a “Review of the “Near
- road Guidance Document

– Outline” and “Near
- road Monitoring Pilot Study Objectives and Approach” (US EPA, 2010i), the CASAC AAMMS cited several other measurements that may be useful or potentially linked to health and welfare effects such as BC, ultrafine particles, and particle size distribution (Russell and Samet, 2010b, pp. xi and xii) . The EPA agrees with these recommendations and encourages monitoring agencies to include these measurements, and others cited in the Subcommittee letter, where possible , in addition to the PM 2.5 mass measurement . The EPA also encourage s monitoring agencies to explore partnerships with instrument manufacturers and researchers to use the sites to evaluate the performance of emerging PM 2. 5 methods in the near
- road environment, especially potential or current FEMs able to provide temporally resolved data and capture the semi
- volatile components of PM 2.5 . Such emerging PM 2.5 methods could be operated as SPMs to provide comparisons to the EPA approved methods supporting compliance to advance the understanding of instrument performance in the near
- road environment . Monitoring agencies are also encouraged to partner with instrument manufacturers and researchers to operate monitors able to measur e other PM properties relevant for the near
- road environment (e.g., ultrafine particles , BC) to provide additional information about exposure to PM in this environment . The EPA is interested in supporting monitoring agencies willing to operate and report the data from these supplemental monitors . The EPA solicits comment on the best way to support such research efforts. The EPA believe s that requiring a modest network of near
- road compliance PM 2.5 monitors is necessary to provide characterization of concen trations in near
- road environments . These long
- term monitors will supplement shorter
- term networks operated by researchers to support the tracking of long
term trends of near - road PM 2.5 mass concentrations and other pollutants in near
- road environments. Th erefore, the EPA proposes to require near
- roadway monitoring of PM 2.5 at one location within each CBSA with a population of one million persons or greater

. The EPA believes that this network will be adequate to support the NAAQS since the largest CBSAs are likely to have greater numbers of exposed populations, a higher likelihood of elevated near
- road PM 2.5 concentrations, and a wide range of diversePage 17 of 36

situations with regard to traffic volumes, traffic patterns, roadway designs, terrain/topography, meteorolog y, climate, surrounding land use and population characteristics . Given the latest population data available, this proposed requirement would result in approximately 5 2 required near
- road PM 2.5 monitors across the country . An indirect benefit of this networ k design is that monitoring agencies in these largest CBSAs are more likely to have redundant monitors that could be relocated to the near
- road environment , reducing costs for equipment and ongoing operation. 11 While only a single PM 2.5 monitor is required within each of the CBSAs, agencies may elect to add additional PM 2.5 monitoring sites in near - road environments. While the EPA recognizes that the location of maximum concentration of PM 2.5 from roadway sources might differ from the maximum location of N O 2 or o t her pollutants, the EPA proposes to require that near
- road PM 2.5 monitors be collocated with the planned NO 2 monitors . The NO 2 network design considers multiple factors that are also relevant for PM 2.5 concentrations (e.g., average annual daily tra ffic and fleet mix by road segment) and significant thought and review has gone into its design, including pilot studies at two locations, and the development of a technical assistance document in conjunction with the affected monitoring agencies and the C ASAC AAMMS (Russell and Samet, 2010b) to support deployment . Further, this collocation will allow multiple pollutants to be tracked in the near
- road environment. Ideally, near
- road sites would be located at the elevation and distance from the road where m aximum concentration of PM 2.5 occur s in this environment, and within reasonable proximity to an area - wide PM 2.5 compliance monitoring site at which a similar PM monitor is used (i.e., for comparison purposes) . Although the EPA is not proposing that the nea r - road PM 2.5 monitors be located within a specific distance of area
- wide sites, monitoring agencies are encouraged to consider that a near
- road site selected in accordance with monitoring requirements and also located in proximity to a robust area
- wide
11 EPA Regional Administrator approval would be required prior to the discontinuation of SLAMS monitors, based on the criteria described in paragraph 58.14(c) to 40 CFR part 58.Page 18 of 36

sit e, such as an NCore station, would provide useful information in characterizing the near
- road contribution to multiple pollutants, including PM 2.5 . The timeline to implement the proposed near
- road PM 2.5 monitors should be as minimally disruptive to on
- goin g operations of monitoring agency programs as possible, while still meeting the need to collect for near
- road PM 2.5 data in a timely fashion . Since the near
- road PM 2.5 monitors are proposed to be collocated with the emerging near
- road NO 2 network that is s cheduled to be operational by January 1, 2013 , the EPA believes it is appropriate to wait until after the near
- road NO 2 network is established before implementing the near
- road PM 2.5 monitors . Therefore, the EPA proposes that each PM 2.5 monitor planned for collocation with a near
- road NO 2 monitoring site be implemented no later than January 1, 2015 . Th e EPA believes th is proposed deadline provides an appropriate amoun t of time for monitoring agencies to select existing PM 2.5 monitors sui table for relocation, receive EPA approval, and physically relocate the PM 2.5 monitor to the near
- road NO 2 site. Based on this proposed timeline, complete data sets (i.e., 3
- years representing 2015
- 2017), from PM 2.5 monitors in the near
- road environment w ould be available to calculate site
- level design values in 2018 . In summary, the EPA proposes to specifically include a near
- road component in the PM 2.5 network design criteria for CBSA’s of 1 million persons or greater, with at least one PM 2.5 monitor collocated with a near
- road NO 2 monitor by January 1, 2015 . The EPA solicits comment on th is approach, especially th e proposed network design requirements ; any alternative strategies that would provide comparable long
- term characterization of PM 2. 5 in area
- wide locations of maximum concentration in the absence of a specific near
- road compliance requirement for monitoring of PM 2.5 ; priorities for the collection of supplemental data at a small subset of near
- road monitoring sites to enhance knowledge of particle exposure (e.g., non
- compliance SPMs); and the interest of monitoring agencies (or other parties) in the collect ion of supplemental (e.g., non
- compliance) measurements relevant for the near
- road environment. ii. Use of PM 2.5 Continuous FEMs at SLAM SPage 19 of 36

The EPA proposes that each agency specify their intention to use or not use data from continuous PM 2.5 FEMs that are eligible for comparison to the NAAQS as part of their annual monitoring network plan due to the applicable EPA Region Office by July 1 ea ch year . The proposal also provides that the EPA Regional Administrator would be responsible for approving annual monitoring network plans where agencies have provided a recommendation that certain PM 2.5 FEMs be considered ineligible for comparison to the NAAQS . In 2006, the EPA finalized new performance criteria for approval of continuous PM 2.5 monitors as either Class III FEMs or ARMs . The EPA has already approved six PM 2.5 continuous FEMs and there are nearly 200 of these monitors already operating in S tate, local, and Tribal networks . Monitoring agencies have been deploying and field
- testing these units over the last couple of years and the EPA recently compiled an assessment of the FEM data in relationship to collocated FRMs (Hanley and Reff, 2011; US EPA, 2011a, pp. 4
- 50 to 4
- 51) . As described in section V I .D.1.a.iii above, the EPA found that some sites with continuous PM 2.5 FEMs have an acceptable degree of comparability with collocated FRMs, while others had poor data comparability that would not meet the performance criteria used to approve the FEMs (71 FR 61285
- 61286, Table C
- 4, October 17, 2006) . The EPA is encouraging u se of the FEM data from those sites with acceptable data comparability including for purposes of comparison to the NAAQS . For sites with unacceptable data comparability, the EPA is working closely with the monitoring committee of the NACAA, instrument manu facturers, and monitoring agencies to document best practices on these methods to improve the comparability and consistency of resulting data wherever possible . Th e EPA believe s that the performance of many of these continuous PM 2.5 FEMs at locations with poor data comparability can be improved to a point where the acceptance criteria noted above can be met. Given the varying data comparability of continuous PM 2.5 FEMs noted above, we believe that a need exists for flexibility in the approaches for how such data are utilized, particularly for the objective of determining NAAQS compliance . Accordingly, we propose that monitoring agencies address the usePage 20 of 36

of data from PM 2.5 continuous FEMs in their annual monitoring network plans due to the applicable EPA Regio nal Office by July 1 of each year for any cases where the agency believes that the data generated by PM 2.5 continuous FEMs in their network should not to be compared to the NAAQS . The annual network plans would include assessments such as comparisons of co ntinuous FEMs to collocated FRMs, and analyses of whether the resulting statistical performance would meet the established approval criteria . Based on these quantitative analyses, monitoring agencies would have the option of requesting that data from conti nuous FEMs be excluded from NAAQS comparison; however, these data could still be utilized for other objectives such as AQI reporting. The issue exists of whether such data use provisions should be prospective only (i.e., future NAAQS comparability exclude d based on an analysis of recent past performance) or a combination of retrospective and prospective (i.e., the implications of unacceptable FEM performance impacting usage of previously collected data as well as future data) . The EPA believes that in most cases, monitoring agencies should be restricted to addressing prospective data issues to provide stability and predictability in the long
- term PM 2.5 data sets used for supporting attainment decisions . However in the first year after this proposed option w ould become effective, we believe it is appropriate to provide monitoring agencies with a one
- time opportunity to review already reported continuous PM 2.5 FEM data and request that data with unacceptable performance be restricted (retrospectively) from NAA QS comparability . Accordingly, in the first year after this rule becomes effective, we propose that monitoring agencies have the option of requesting in their annual monitoring network plans that a portion or all of the existing continuous PM 2.5 FEM data, as applicable, as well as future data, be restricted from NAAQS comparability for the period of time that the plan covers. 12 Annual monitoring network plans in subsequent years would only need to cover new data for the period of time that the plan covers. As noted above, in cases where an agency is operating a PM 2.5 continuous FEM that is not
12 Data from any PM 2.5 monitor being used to meet minimum monitoring requirements could not be restricted from NAAQS comparability.Page 21 of 36

meeting the expected performance criteria used to approve the FEMs (71 FR 61285 to 61286, Table C
- 4, October 17, 2006) when compared to their collocated FRMs, an agenc y can recommend that the data not be used for comparison to the NAAQS . However, all required SLAMS would still be required to have an operating FRM (or other well performing FEM, as evidenced by a prior collocation with an FRM) to ensure a data record is a vailable for comparison to the NAAQS . In cases where a PM 2.5 continuous FEM was not meeting the expected performance criteria, and the Regional Administrator has approved that the FEM data will not be considered eligible for comparison to the NAAQS, the da ta would still be required to be loaded to AQS; however, these data would be stored separately from data used for comparison to the NAAQS . The goal of proposing to allow monitoring agencies the opportunity to recommend not having data from PM 2.5 continuou s FEMs as comparable to the NAAQS is to ensure that only high quality data (i.e., data from FRMs which are already well established and new continuous FEMs that meet the performance criteria used to approve FEMs when compared to collocated FRMs operated in each agencies network) are used when comparing data to the PM 2.5 NAAQS . Under the current monitoring regulations, a monitoring agency can identify a PM 2.5 continuous FEM as a n SPM, which allows the method to be operated for up to 24 months without its dat a being used in comparison to the NAAQS . While 24 months should be sufficient time to operate the method across all seasons, assess the data quality, and in some cases resolve operational issues with the instrument, it may still leave some agencies with me thods whose data are not sufficiently comparable to data from their FRMs . In these cases there may be a disincentive to continue operating the PM 2.5 continuous FEM, especially in networks where the monitoring data is near the level of the NAAQS . With the p roposed provision where a monitoring agency can recommend not having data from PM 2.5 continuous FEMs as comparable to the NAAQS, a monitoring agency can continue to operate their PM 2.5 continuous FEM to support other monitoring objectives (e.g., diurnal characterization of PM 2.5 , AQI forecasting and reporting), while working through options for improved data comparability.Page 22 of 36

The EPA believes that an assessment of FEM performance should in clude several elements based on the original performance criteria . Th e Agency also believe s that certain modifications to the performance criteria are appropriate in recognition of the differences between how monitoring agencies operate routine monitors ve rsus how instrument manufacturers conduct required FRM and FEM testing protocols . The details below summarize these issues . The EPA proposes to use the performance criteria used to approve the FEMs (71 FR 61285 to 61286, Table C
- 4, October 17, 2006) for th ose agencies that recommend not having data from PM 2.5 continuous FEMs as comparable to the NAAQS . To accommodate how routine monitoring networks operate, the EPA proposes that agencies seeking to demonstrate insufficient data comparability in an assessmen t base the analysis mainly on collocated data from FRMs and continuous FEMs at monitoring stations in their network . The EPA does not believe it is practical to utilize the requirement in table C
- 4 of 40 CFR part 53 for having multiple FRMs and FEMs at eac h site since such arrangements are not typically found in monitoring agency networks . Accordingly, the requirement for assessing intra
- method replicate precision would be inapplicable . Another consideration is the range of 24
- hour data concentrations, for instance, the performance criteria in table C
- 4 of 40 CFR part 53, provides for an acceptable concentration range of 3 to 200 μg/m 3
. However, the EPA note s that during an evaluation of data quality from two FEMs (US EPA, 2011a, p. 4
- 50), th e Agency found t hat including low concentration data were helpful for understanding whether an intercept or slope was driving a potential bias in an instrument . Therefore, the EPA proposes that agencies may include low concentration data (i.e., below 3 μg/m 3 ) for purposes of evaluating the data comparability of continuous FEMs . With regard to the minimum number of samples needed for the assessment, the EPA note s that a minimum of 23 sample pairs are specified for each season in table C
- 4 of 40 CFR part 53 . Having 23 sample pairs per season should be easily obtainable within one year for sites with a FRM operating on at least a 1 in 3 day sample frequency and we propose that this requirement be applicable to the assessments being discussed here . For sites on a one in 6 day s ampling frequency, two years of data may be necessary to meet this requirement . The EPA recognizes that itPage 23 of 36

would be best to assess the data based on the most recently available information; however, having data across all seasons in multiple years will pro vide a more robust data set for use in the data comparability assessment; therefore , the EPA proposes that data quality assessments be permitted to utilize up to the last three years of data for purposes of recommending not having data from PM 2.5 continuou s FEMs as comparable to the NAAQS. The EPA recognizes that only a portion of continuous PM 2.5 FEMs will be collocated with FRMs, and it would be impractical to restrict the applicability of data comparability assessments to only those sites that had colloc ated FRM and FEM monitors . In these cases, the monitoring agency will be permitted to group the sites that are not collocated with an FRM with another similar site that is collocated with an FRM for purposes of recommending that the data are not eligible for use in comparison to the NAAQS . Monitoring agencies may recommend having PM 2.5 continuous FEM data eligible for comparison to the NAAQS from locations where the method has been demonstrated to provide acceptable data comparability, while also recommend ing not having it eligible in other types of areas where the method has not been demonstrated to meet data comparability criteria . For example, a rural site may be more closely associated with aged particles where volatilization issues are minimized result ing in acceptable data comparability between filter
- based and continuous methods, while a highly populated urban site with fresh emissions may result in higher readings on the PM 2.5 continuous FEM that would not meet the expected performance criteria as co mpared to a collocated FRM . In all cases where a monitoring agency chose to group sites for purposes of identifying a subset of PM 2.5 continuous FEMs that would not be comparable to the NAAQS, the assessment submitted with the annual monitoring network pla n would have to provide sufficient detail to support the identification of which combinations of method and sites would, and would not, be comparable to the NAAQS, as well as the rationale and quantitative basis for the grouping and recommendation. The EPA solicits comment on all aspects of this proposed approach of allowing monitoring agencies to recommend that PM 2.5 continuous FEM data should not be compared to the NAAQS, whenPage 24 of 36

demonstrated to not meet the performance criteria used to approve FEMs based on data in their own network, and as appropriate, approved by the EPA Regional Administrators as ineligible for comparison to the NAAQS. c. Revoking PM 10
- 2.5 Speciation Requirements at NCore Sites The EPA issued revisions to the Ambient Air Monitoring Regulations (40 CFR parts 53 and 58) on October 17, 2006 (71 FR 61236) . In the 2006 final rule, the EPA required that PM 10
- 2.5 speciation be conducted at NCore multi
- pollutant monitoring stations by January 1, 2011 . PM 10
- 2.5 speciation at NCore was intende d to support further research in the understanding of the chemical composition and sources of PM 10 , PM 10
- 2.5 and PM 2.5 at a variety of urban and non
- urban NCore locations . Subsequent to the completion of the 2006 final monitoring rule, several technical is sues were raised concerning the readiness of PM 10
- 2.5 speciation monitoring methodologies to support such a nation
- wide deployment strategy . Based on these issues and as explained in detail below, the EPA proposes to revoke the requirement for PM 10
- 2.5 spe ciation monitoring as part of the current suite of NCore monitoring requirements . The requirement to monitor for PM 10
- 2.5 mass (total) at all NCore multi
- pollutant sites remains . Monitoring was commenced on January 1, 2011 as part of the nationwide startup of the NCore network (US EPA, 2011a, p. 1
- 15). As part of the process to further define appropriate techniques for PM 10
- 2.5 speciation monitoring, a public consultation with the CASAC AAMMS on monitoring issues related to PM 10
- 2.5 speciation was held in F ebruary 2009 (74 FR 4196, January 23, 2009) . At that time, the subcommittee noted the lack of consensus on appropriate sampling and analytical methods for PM 10
- 2.5 speciation and expressed concern that the Agency’s 2006 commitment to launch the PM 10
- 2.5 mo nitoring network without sufficient time to analyze the data from a planned pilot project was premature (Russell, 2009) . Based on the noted lack of consensus on PM 10
- 2.5 speciation monitoring techniques, the Agency did plan and implement a small pilot moni toring project to evaluate the available monitoring and analytical technologies and supplement the PM 10
- 2.5 speciation measurements that have mostly been done as part of other research efforts . ThePage 25 of 36

EPA expects that this field study will address the issues needed to develop a more robust, long
- term PM 10
- 2.5 speciation monitoring plan. The EPA pilot monitoring project will be completed in 2011, with plans to analyze the data and prepare a final report on findings and recommendations in 2012 . At that time, th e EPA will consider what PM 10
- 2.5 speciation sampling techniques, analytical methodologies, and network design strategies would be most appropriate as part of a potential nation
- wide monitoring deployment . Such a deployment could be based on the NCore multi
- pollutant framework, or some other strategy that targets such measurements in areas with higher levels of coarse particles . This latter type of strategy would be consistent with CASAC AAMMS members written comments that not all NCore sites would be a dequate for PM 10
- 2.5 speciation and that more flexibility in PM 10
- 2.5 speciation network design would allow for a geographically diverse network to support health studies and research (Russell, 2009). The EPA may consider reintroducing some PM 10
- 2.5 specia tion monitoring requirements in a subsequent monitoring rulemaking or as part of a future review of the PM NAAQS . Until that time, the EPA believes it is appropriate to propose to revoke the current set of PM 10
- 2.5 speciation monitoring requirements . The E PA solicits comment on this proposed revision to monitoring requirements. d. Measurements for the Proposed New PM 2.5 Visibility Index NAAQS The EPA proposes requirements for sampling of PM 2.5 chemical speciation in states with large CBSAs . The CSN has been op erating for approximately 10 years and as described earlier in this proposal already supports a number of important monitoring objectives . Since the CSN network is already well established in states with large CBSAs, the EPA believes that using the data fr om these existing sites as an input for calculating PM 2.5 visibility index values will help ensure that the network can continue to support existing objectives, while also supporting the proposed new secondary standard. To ensure the CSN network can suppo rt its existing network objectives while also supporting the proposed new secondary PM 2.5 visibility index standard ( section V I . F) , the EPA proposes that each state with a CBSA over 1 million have measurements based on the methods in CSN (or IMPROVE), asPage 26 of 36

d iscussed in section VI I . A .5 above , in at least one of its CBSAs . For states with urban or suburban NCore Stations, their existing CSN measurements at all NCore sites would be appropriate to meet this proposed requirement . For states with multiple high population CBSAs, the EPA proposes that each CBSA with a population over 2.5 million people be required to have CSN measurements . The EPA does not believe it would be appropriate to require multiple cities in the same state to have CSN measurements for purposes of supporting the proposed new secondary PM 2.5 visibility index standard when these cities have relatively smaller populations (i.e., less than 2.5 million people) as the chemical species data may be similar across citie s in the same state . The exception to this will be the most highly populated states and cities, which are either already covered by requirements for multiple NCore stations or the proposed population threshold of 2.5 million people . For example, the follow ing high population states are already required to have multiple NCore stations: California, Florida, Illinois, Michigan, New York, North Carolina, Ohio, Pennsylvania, and Texas . The EPA also proposes that states be allowed to request alternative CBSAs to locate their CSN measurements, when the alternative location is better suited to support providing data for multiple monitoring objectives, including for the proposed new secondary PM 2.5 visibility index standard . For example, in some cases a large CBSA wi th a marine influence may have relatively cleaner air than a smaller inland CBSA in the same state with a lower population . In these cases , states may request an alternative location for their CSN measurements . The EPA solicits comment of these proposed re quirements and on alternative requirements for CSN measurements to support the proposed new secondary PM 2.5 visibility index standard . The EPA proposes that the network design criteria for CSN measurements focus on area
- wide locations that are generally re presentative of long distances throughout a CBSA . For most CBSAs, this will mean that the existing inventory of CSN measurements can be used where the location of the sampling equipment is at an NCore station or other station(s) sited at the neighborhood o r urban scale of representation . The EPA points out that while the existing PM 2.5 network design criteria established to support the primary PM 2.5 NAAQS focuses on the area
- wide locations of expected maximumPage 27 of 36

concentration, there would not necessarily be th e same focus for the proposed new secondary PM 2.5 visibility index standard . One reason for this difference is that for urban visibility , we are interested in the impact of visibility degradation over as representative a location as possible as the impact of the aerosol is a function of an entire site path and not just one monitoring location within a CBSA . Also, the EPA is interested in leveraging as much of the existing inventory of CSN and IMPROVE measurements operating in CBSAs where they can support th e proposed new secondary PM 2.5 visibility index standard. The EPA considered the issue of siting measurements to support a new secondary standard to address PM
- related visibility impairment during a consultation with the CASAC AAMMS (75 FR 4069, January 2 6, 2010) . In its letter to the EPA, the CASAC AAMMS stated that “the Subcommittee strongly favored collocation of extinction measurements with PM mass, PM speciation, and precursor gas measurements, identifying continuous PM mass and speciation measurement s as being of particular value . NCore multi
- pollutant monitoring sites were identified as worth considering even though these would not necessarily capture maximum concentrations and visibility impairment in an urban area” (Russell and Samet, 2010a, p. 18) . The EPA notes that the Subcommittee also identified that “[t]here was general support for making public communication an important consideration in network design, for example by selecting a monitoring site that can be associated with a vista that is recog nized by a significant fraction of the local population” (Russell and Samet, 2010a, p. 18) . While the EPA agrees that siting associated with a recognizable vista would be a useful consideration for establishing new sites, the EPA does not believe it would be appropriate to include such a requirement for cities with existing sites as this may disrupt the use of data to meet other important monitoring objectives . The EPA also notes existing long
- standing public communication tools such as the “Haze
- Cam” netwo rk are already well suited for public communications of important vistas. 13 In addition to collocation with several important measurements at NCore as cited by the Subcommittee, the EPA is also encouraging monitoring agencies to add other important measurem ents such as commercially available technologies 13 See http://www.hazecam.net/ .Page 28 of 36

for light absorption and light scattering; however, the EPA does not believe these technologies should be specified by regulation. Since EPA ’ s proposal to require CSN (or IMPROVE) sampling is consistent wit h a network that is largely already in place, there is no expectation new sites will be needed . However, from time to time there is a disruption of sampling due to loss of a sites lease agreement or other circumstances . Therefore, for any state that does n ot have a minimally required CSN (or IMPROVE) set of measurements in place, the EPA proposes that these measurements be in place and sampling by January 1, 2015. 4. Proposed Revisions to the Quality Assurance Requirements for SLAMS, SPMs, and PSD a . Quality A ssurance Weight of Evidence The EPA believes that the process by which monitoring organizations and the EPA use the appendix A of 40 CFR part 58 regarding quality assurance requirements in regulatory decision making needs to be articulated . Prior interpret ations of appendix A have led to disqualification of data for noncompliance with a particular appendix A requirement . The proposed language described below, provides the interpretation the EPA would use moving forward. The appendix A to 40 CFR part 58 req uirements represent a portion of the quality control activities that are implemented by monitoring organizations to control data quality . The EPA believes that while it is essential to require a minimum set of checks and procedures in appendix A to support the successful implementation of a quality system, the success or failure of any one check or series of checks does not preclude the EPA from determining that data are of acceptable quality to be used for regulatory decision
- making purposes . The EPA propo ses to use a weight
- of
- evidence approach for determining whether the quality of data is appropriate for regulatory decision
- making purposes . Furthermore, the suitability of data for any regulatory purpose also relies, in part, on several other quality
- rela ted requirements found elsewhere in 40 CFR part 58 . These requirements include air monitoring methodology (appendix C), network design criteria (appendix D) and network design plans for SLAMS, probe siting criteria (appendix E), the reporting of data to AQ S, data completeness, andPage 29 of 36

data certification by the reporting organization . This weight of evidence approach recognizes that all measurement systems have uncertainty and there are numerous factors that can affect data quality at a particular monitoring sit e . The specific appendix A criteria are designed to provide a quantification of this uncertainty, support a framework for assessing such uncertainty against known data quality goals and to support corrective actions when necessary to control uncertainty back to acceptable levels . Accordingly, the EPA proposes additional wording in appendix A to clarify the role that appendix A generated data quality indicators have in the overall quality system that supports ambient air monitoring activities . b. Quality Assurance Requirements for the Chemical Speciation Network The EPA proposes to include requirements for flow rate verifications and flow rate audits for the PM 2.5 CSN . These audits are currently being performed so , although they will be considered a new re quirement, they are not new implementation activities . In addition, the CSN already includes six collocated sites which the EPA proposes to include in the 40 CFR part 58 appendix A requirements . The EPA proposes that PSD sites would not be required to coll ocate a second set of instruments for speciated PM 2.5 mass monitoring. The EPA is currently undertaking an assessment of measurement uncertainty from the collocated CSN and IMPROVE stations in order to support establishing data quality goals for the chemic al speciation measurements used in the proposed calculated light extinction indicator . Once these goals are identified they may be included in regulation and technical guidance. c. Waivers for Maximum Allowable Separation of Collocated PM 2.5 Samplers and Moni tors The EPA proposes to allow waivers for the maximum allowable distance associated with collocated PM 2.5 samplers and monitors . As described in section VII I .A.1 of this proposal, the EPA has already approved six Class III PM 2.5 continuous FEMs . Several o f these approved FEMs are required to be installed in a shelter with sufficient control of heating and air conditioning to ensure stable operation of the instrument . In many cases monitoring agencies are installing these approved continuous FEMs inPage 30 of 36

shelter s where they already have gas analyzers operating . Some agencies operate filter
- based samplers (e.g., PM 2.5 FRMs) on top of their shelter, while others operate platforms next to their shelter . In either case, ensuring PM 2.5 continuous FEMs and PM 2.5 FRMs m eet collocation requirements (i.e., 1 to 4 meters for PM 2.5 samplers with flow rates of less than 200 liters/minute) can be challenging, since in some cases multiple instruments, some installed in the shelter and some installed on a platform, are being sit ed at the same station. The EPA believes that maintaining the current requirement of 1 to 4 meters for PM 2.5 samplers with flow rates of less than 200 liters/minute is useful since it ensures consistency with long
- standing practices of collocation and ensu res that any air drawn through collocated samplers is well within the operational precision of the instruments . However, the EPA also believes that instruments spaced farther apart could also be within the operational precision of the instruments, especial ly at sites located at larger scales of representation (e.g., neighborhood scale and larger) . The EPA already defines a collocated scale in its document “Guidance for Network Design and Optimum Site Exposure for PM 2.5 and PM 10 (US EPA, 1997) . In this docum ent, the EPA defines a collocated scale as 1 to 10 meters . The EPA believes that almost all agencies would be able to site collocated PM samplers and monitors within 10 meters . Therefore, the EPA proposes to allow waivers, when approved by the EPA Regional Administrator, for collocation of PM 2.5 samplers and monitors of up to 10 meters so long as the site is at a neighborhood scale or larger . The EPA solicits comment on this proposed change to allow waivers of the maximum allowable distance for collocated P M 2.5 samplers and monitors. 5. Proposed Probe and Monitoring Path Siting Criteria a. Near
- road Component to the PM 2.5 Monitoring Network The EPA proposes that the probe and siting criteria for the near
- road component to the PM 2.5 monitoring network design follo w the same probe and siting criteria as the NO 2 near - road monitoring sites . These requirements would provide that the monitoring probe be sited “...as near as practicable to the outside nearest edge of the traffic lanes of the target road segments; but shall not be located at aPage 31 of 36

distance greater than 50 meters, in the horizontal, from the outside nearest edge of the traffic lanes of the target road segment” (section 6.4 of appendix E to 40 CFR part 58) . The EPA solicits comment on this proposed probe and sitin g criteria for the proposed near
- road component to the PM 2.5 monitoring network design. b. CSN Network The EPA proposes to extend the existing probe and monitoring path siting criteria described in appendix E to 40 CFR part 58 for PM 2.5 FRMs and FEMs to the C SN measurements . The EPA believes that monitoring agencies are already following the probe and siting criteria for PM 2.5 when conducting CSN measurements; that is , at neighborhood, urban, and regional scale sites the probe height must be 2 to 15 meters abo ve ground level . All other aspects of the existing PM 2.5 probe and siting criteria would also apply including minimum distances from horizontal supporting structures (i.e., greater than 2 meters) and minimum distance to the drip
- line of a tree (i.e., great er than 10 meters) . The IMPROVE program SOP (IMPROVE , 1996 ) on site selection already provides for meeting probe and siting criteria described in Appendix E . The EPA solicits comment on extending the existing probe and siting criteria for PM to the speciat ion measurements used to support the proposed new secondary PM 2.5 visibility index standard. c. Reinsertion of Table E
- 1 to Appendix E The EPA is proposing to reinsert t able E
- 1 to a ppendix E of 40 CFR p art 58 . T his t able presents the minimum separation dista nce between roadways and probes or monitoring paths for monitoring neighborhood and urban scale ozone (O 3 ) and oxides of nitrogen (NO, NO 2 , NO x , NO y ) . This table was inadvertently removed during a previous CFR revision process . The EPA is utilizing this proposed rule to reinsert this table, unchanged from its prior iteration, back into the CFR . 6. Additional Ambient Air Monitoring Topics a. Annual Monitoring Network Plan and Periodic AssessmentPage 32 of 36

In October of 2006, the EPA finalized new requirements for each state, or where applicable, local agency to perform and submit to their EPA Regional Offices an Assessment of the Air Quality Surveillance System (40 CFR 58.10) . This assessment is required every five years . The first required five year assessments were su bmitted to EPA Regional Offices on or before July 1, 2010 . The assessments are intended to provide a comprehensive look at each monitoring agencies ambient air monitoring network to ensure that the network is meeting the minimum monitoring objectives defin ed in appendix D to 40 CFR part 58, whether new sites are needed, whether existing sites are no longer needed and can be terminated, and whether new technologies are appropriate for incorporation into the ambient air monitoring network. 14 Since each state h as completed their first required five
- year assessment, and several monitoring rule requirements have either been added or changed since this requirement was added in 2006, the EPA thinks it is appropriate to review this requirement and solicit comment on any possible changes the EPA should consider that may improve the usefulness of the assessments . Specifically, the EPA solicits comment on ways to either streamline or add additional criteria for future assessments . Even if no changes to the requirements a re recommended by any commenters, the EPA is especially interested in learning from monitoring agencies that may have ideas on how to improve future assessments . Such ideas may not necessarily have to be incorporated into regulation, but could be referred to in our guidance on network assessments (US EPA, 2007b). The EPA proposes to remove references to “community monitoring zones” and “spatial averaging” in the annual monitoring network plans due to EPA Regional Offices by July 1 of each year . The Agency proposes to remove these references since, as discussed in section VI I .A.2 above, the EPA is proposing to remove all references to the spatial averaging option throughout 40 CFR part 50 appendix N . Consistent with these changes, the EPA also proposes to remove references to community 14 The EPA provides a link to these assessments on EPA’s website at: http://www.epa.gov/ttn/amtic/plans.html . A detailed description of the requirements for the assessments is described in 40 CFR 58.10.Page 33 of 36

monitoring zones under the annual monitoring network plans described in 40 CFR 58.10 . b. Operating Schedules The EPA generally requires PM 2.5 SLAMS to operate on at least a 1
- day
- in
- 3 sampling schedule, unl ess a reduced sampling frequency is approved such as might be the case with a site that has a collocated continuous operating PM 2.5 monitor. 15 However, in the 2006 monitoring rule amendments, the EPA finalized a new requirement for the operating schedule of PM 2.5 SLAMS sites (40 CFR 58.12) . The new requirement stated that sites with a design value within plus or minus five percent of the 24
- hour PM 2.5 NAAQS must have an FRM or FEM operating on a daily sampling schedule . This requirement was included to minim ize any statistical error associated with the form of the 24
- hour PM 2.5 NAAQS (i.e., the 98 th percentile) . In section II I .F, the Administrator is proposing to revise the level of the primary annual PM 2.5 NAAQS . Accordingly, she is now considering whether t his proposed change should result in any changes to sampling frequency requirements. The EPA had previously considered how sample frequency affects the Data Quality Objectives in a consultation with the CASAC AAMMS in September of 2005 (70 FR 51353 to 513 54, August 30, 2005) . As a result of that consultation, the EPA proposed (71 FR 2710 to 2808, January 17, 2006) and finalized (71 FR 61236 to 61328, October 17, 2006) changes to the sample frequency requirements as part of the monitoring rule changes in 20 06 . In that work, the EPA demonstrated that having a higher sample count is generally more useful to minimize uncertainty for a percentile standard than an annual average . Given the proposed strengthening of the primary annual PM 2.5 NAAQS and the known bur den of performing daily sampling using the filter
- based samplers that are still a mainstay in monitoring agency networks, the issue of needing daily sampling for sites that have design values close to the level of the 24
- hour PM 2.5 standard should be recon sidered if the site already has a design value above the level of the primary annual PM 2.5 NAAQS . 15 All NCore stations must operate on at least a one
- in
- three day sampl e frequency for filter
- based PM sampling.Page 34 of 36

In a related issue, since the EPA finalized the requirement for daily sampling at sites within 5 percent of the 24
- hour PM 2.5 NAAQS in 2006, there has been c onfusion over the procedures for adjusting sample frequencies, where necessary, to account for variations in year
- to - year design values . Therefore, the EPA proposes to revise this requirement in the following ways: (1) The EPA proposes that monitors would only be required to operate on a daily schedule if their 24
- hour design values are within five percent of the 24
- hour PM 2.5 NAAQS and the site has a design value that is not above the level of the annual PM 2.5 NAAQS . (2) The EPA proposes that review of dat a for purposes of determining applicability of this requirement at a minimum be included in each agency’s annual monitoring network plan described in 40 CFR 58.10 based on the three most recent years of ambient data that were certified as of the May 1 dead line . However, monitoring agencies may request changes to sample frequency at any time of the year by submitting such a request to their applicable EPA Regional Office . Changes in sampling frequency are expected to take place by January 1 of the following year . Increased sampling is expected to be conducted for at least three years, unless a reduction in sampling frequency has been approved in a subsequent annual monitoring network plan or otherwise approved by the Regional Administrator . The EPA solicits c omment on these proposed changes to the required operating schedule for PM 2.5 SLAMS. c. Data Reporting and Certification for CSN and IMPROVE Data The EPA solicit s comment on minor changes to reporting and certification of data associated with CSN and IMPROVE data . The chemical analyses of filters associated with CSN measurements results in reporting of data that are usually within three months of the sample collection . This fits within the existing reporting requirements for most ambient air measurements that data be reported within 90 days past the end of the previous quarterly reporting period (40 CFR 58.15) . However, some agencies also use IMPROVE or their own internal laboratory for processing of chemical analyses . IMPROVE is known to validate and report i ts data on a schedule that is approximately 12 to 18 months after sample collection . At least one state laboratory continues to provide chemical analysis of filters associated withPage 35 of 36

sites that are not NCore (note: all NCore stations use either IMPROVE or th e CSN National Laboratory contractor for their speciation laboratory analysis) . Therefore, the EPA solicits comment on including the existing reporting requirements when reporting CSN measurements . In addition, the EPA also solicits comment on a longer rep orting and certification 16 schedule specifically for CSN and IMPROVE that appropriately balances having sufficient time to analyze, validate, and report data with the need to have the data in sufficient time to use in assessments including calculating the p roposed PM 2.5 visibility index values discussed in section VII.A.5 above . Since 2010, the EPA has required states to certify their data by May 1 of each year . Since in some cases chemical speciation data may not be fully validated and submitted to EPA by M ay 1 of a given year, the EPA solicits comment on having data certification of these speciation measurements take place by May 1 of the following year . For example, if the fourth quarter chemical speciation data were not fully available to certify by May 1 of the following year, it would be certified another 12 months after that . The EPA solicits comment on the reporting and certification schedules for chemical speciation data. d. Requirements for Archiving Filters The EPA proposes to extend the requirement fo r archival of PM 2.5 , PM 10 , and PM 10
- 2.5 filters from manual low
- volume samplers (samplers with a flow rate of less than 200 liters/minute) at SLAMS from one year after data collection to five years after data collection . The archive of low
- volume PM filter s is an important tool for on
- going research and development of emission control strategies and for use in health and epidemiology research . During a workshop on Ambient Air Quality Monitoring and Health Research in 2008, retaining filters for laboratory analysis was identified as a key recommendation to provide daily measurements of metals and elements (US EPA, 2008d, pp. 17 to 21) . The EPA’s current requirement of one
- year is not sufficiently long for retrospective analysis of important episodes and for use in long
- term epidemiology research . Since first requiring filter archival of low
- volume PM filters in 1997, the EPA has always recommended longer filters archives and most 16 Data certification requirements are described in 40 CFR 58.15 .Page 36 of 36

agencies are already doing so . However, a small number of agencies have reported discarding older filters, despite the minimal cost of storing these filters . Since cold storage of a large number of filters may be cost prohibitive and of little benefit in retaining key aerosol species in the x
- ray fluorescence (XRF) analyses, the EPA p roposes to minimize the costs of retaining filters by only requiring cold storage during the first year after sample collection . Therefore, the EPA solicits comment on this proposal to extend the filter archival requirement from one to five years, but only requir e cold storage during the first year.