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From: Lydia Wegman/RTP/USEPA/US

To: nfrey@omb.eop.gov

Cc: Richard Wayland/RTP/USEPA/US@EPA, Lewis Weinstock/RTP/USEPA/US@EPA, Tim 

Hanley/RTP/USEPA/US@EPA, James Hemby/RTP/USEPA/US@EPA, Beth HassettSipple/RTP/USEPA/US@EPA, Joseph-J Dougherty/DC/USEPA/US@EPA, Padmini 

Singh/DC/USEPA/US@EPA, Susmita Dubey/DC/USEPA/US@EPA

Date: 06/12/2012 05:50 PM

Subject: Further revisions to the monitoring provisions of the PM NAAQS preamble

Nathan, 

In response to the comments you gave me this morning concerning the monitoring and implementation sections 

of the preamble, we have made several revisions to those sections. We believe these are responsive to the 

issues you raised during our discussion. 

The attachment below addresses the monitoring issues. It compares our changes to the version of the preamble 

that accepted all previous edits we have made in response to interagency comments so that readers can see the 

most recent changes clearly. The changes are as follows:

1. We added language in the micro/middle-scale section attempting to explain how this provides more 

consistency and predictability and thus reduces the burden on States. (See pages 9 - 11) 

2. We added language to the near-road section of the preamble to explain the burden reduction associated with 

moving from single pollutant to multi-pollutant sites and using the existing NO2 network design, as well as 

describing other flexibilities. (See pages 12-18) 

3. We corrected a reference in the QA section assessing CSN measurement uncertainty. (Page 29)

I will shortly be sending you the changes to the implementation section. 

Lydia
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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 (“monitoring 

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 III.F, IV.F, and VI.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 

alternative methods where explicitly stated in the monitoring methodology requirements (appendix C of 

40 CFR part 58), such as PM2.5 ARMs which can be used to determine compliance with the NAAQS. 

The EPA prescribes testing and approval criteria for FRM and FEM methods in 40 CFR part 53.

1. PM2.5 and PM10-2.5 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 PM2.5 or 

PM10-2.5 that utilize a PM2.5 sampler or PM10-2.5 sampler in which integrated PM2.5 samples or PM10-2.5

samples are obtained from the atmosphere by filtration and are then subjected to a filter conditioning 

process followed by gravimetric mass determination. 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 PM2.5 or PM10-2.5 that are employed to provide PM2.5 or PM10-2.5

ambient air measurements representative of one-hour or less integrated PM2.5 or PM10-2.5 concentrations, 

as well as 24-hour measurements determined as, or equivalent to, the mean of 24 one-hour consecutive 
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measurements. These new testing and performance criteria were developed by the EPA and reviewed 

through consultation with the CASAC AAMMS1and 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 PM10-2.5 Class II manual methods, one Class III PM10-2.5 continuous method, and six Class 

III PM2.5 continuous methods.2

While the EPA has approved these PM2.5 Class III continuous FEMs, only two of those methods 

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 PM2.5 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 approve the 

FEMs.

The EPA continues to believe that an effective PM2.5 monitoring strategy includes the use of 

both filter-based FRM samplers and well-performing continuous PM2.5 monitors. Well-performing 

continuous PM2.5 monitors would include both non-approved continuous PM2.5 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 SLAMS is described in more detail in section VIII.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.
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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 efficiency 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 PM2.5 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 PM2.5 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 

performing 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 PM2.5 FEMs. While some agencies 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 PM2.5 continuous FEMs before considering 

any changes to regulatory testing 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 

PM2.5 continuous methods and collocated FRMs (assessments across the country are 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 testing criteria in 40 CFR part 53 used to approve PM2.5 continuous FEMs. 

While EPA is not proposing any changes to the performance or testing criteria in 40 CFR part 53 

used to approve PM2.5 continuous FEMs, the EPA proposes an administrative change to part 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 this 
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section reads, “Any analyzer, PM10 sampler, PM2.5 sampler, or PM10-2.5 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 acceptance 

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 PM2.5 and PM10-2.5; however, there is no specific reference to performance criteria 

for Class II and III PM2.5 and PM10-2.5 methods. Therefore, the EPA proposes to link the performance 

criteria referred to in 40 CFR part 53.35 associated with Class II and III PM2.5 and PM10-2.5 methods with 

this requirement for maintaining designation of approved FEMs. The specific performance criteria 

identified in 40 CFR 53.35 for PM2.5 and PM10-2.5 methods are available in table C-4 to subpart C of 40 

CFR part 53. 

2. Use of CSN Methods to Support the Proposed New Secondary PM2.5 Visibility Index NAAQS

The EPA, monitoring agencies, and external scientists and policy makers use PM2.5 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 quality; 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.3The 

 

3

In the IMPROVE program, artifact adjusted OC (i.e., PM2.5 OC) is simply reported as OC. That is the 

value used to produce OM for haze calculations. For the CSN measurements, the OC artifact needed to 

convert measured OC into PM2.5 OC is estimated from sampler-specific network-wide field blanks 

(Frank, 2012).
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CSN measurements 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). The CSN network is 

described in the Policy Assessment (US EPA, 2011a, Appendix B, section B.1.3). 

As noted in section VI.D.1.c above, the proposed new secondary standard for PM2.5 to address 

PM-related visibility impairment is defined in terms of a PM2.5 visibility index, which would use PM2.5

speciation measurement data. The EPA proposes that measurements using either the CSN or IMPROVE 

methods4be eligible for use to calculate PM2.5 visibility index values. The EPA believes this proposed 

approach is appropriate because the methods for CSN and IMPROVE are well documented5in 

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 PM2.5 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 PM2.5 visibility index would do so by following the methods and SOPs publically available on 

both the IMPROVE or the EPA (for CSN) websites.6The 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. 

5CSN 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 program 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 available 
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include the CSN and IMPROVE measurements by reference and not require that such methods be 

approved as FRMs.

As discussed in section VII.A.5 above, the calculation of the PM2.5 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 PM2.5 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 “areawide.” The term “community-oriented,” while used within the description of the design criteria for 

PM2.5, 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 PM2.5 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 PM2.5 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 micro-or middle-scale that are representative of many such locations in 

 

in Docket number EPA-HQ-OAR-2007-0492 and on the IMPROVE website at: 

http://vista.cira.colostate.edu/improve/publications/IMPROVE_SOPs.htm. 
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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 optional averaging area 

with established, well defined boundaries, such as county or census block, within an MPA that has 

relatively uniform concentrations of annual PM2.5 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 PM2.5 NAAQS.” The EPA proposes to revoke this term 

and references to it since, as discussed in section VII.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 PM2.5 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 methods 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 PM2.5

monitoring requirements are additional restrictions prescribed within the monitoring rules.7These 

additional restrictions provide that sites must be “population-oriented” for comparison 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 PM2.5 concentration. 

The inclusion of these provisions in the PM2.5 monitoring requirements since the 1997 

 

7

These are referenced in 40 CFR 58.30 (Special considerations for data comparisons to the NAAQS). 
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promulgation of the PM2.5 NAAQS and associated monitoring requirements has resulted in substantial 

ambiguity when the EPA and state, local, and tribal agencies consider the design of PM2.5 monitoring 

networks as NAAQS are revised as well as how unmonitored locations should be treated in modeling 

exercises.8 Accordingly, the EPA proposes to revise these particular PM2.5 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 PM2.5 Monitoring 

Sites to the NAAQS

The EPA proposes to revoke the requirement that PM2.5 monitoring sites be “populationoriented” for comparison to the NAAQS. This requirement is inconsistent with our definition of ambient 

air which the NAAQS employ. The EPA’s definition of ambient 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 - “Populationoriented monitoring (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 PM2.5 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 PM2.5 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 

 

8 Modeling can be associated with either PSD or transportation conformity as discussed in sections IX.F 

and IX.G, respectively, below.
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existing sites are treated (as explained below there are no remaining sites designated as not being 

“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 PM2.5 monitoring 

network, the EPA notes that there are no remaining sites operating affirmatively as “non populationoriented.” 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 up 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 PM2.5 monitor that provides high time-resolution data, but is 

not approved as an FEM. Even if a monitoring agency wanted to use an FRM, an agency could still 

operate a monitor for up to 24 months as an 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 PM2.5 NAAQS

The EPA is clarifying language used to determine when PM2.5 monitoring sites at micro- and 

middle-scale locations are comparable to the annual NAAQS. EPA’s intent in clarifying this language is 

to provide consistency and predictability in the interpretation of the monitoring regulations to minimize 

the burden on state monitoring programs as they plan and implement their monitoring programs. The 

EPA’s current rules, as specified in 40 CFR 58.30, state that “PM2.5 data that are representative, not of 

area-wide but rather, 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 
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PM2.5 NAAQS. For example, if the PM2.5 monitoring site is adjacent to a unique dominating local PM2.5

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 PM2.5 NAAQS.” The EPA is clarifying language to explicitly state that measuring PM2.5 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 PM2.5 monitoring site, even micro- and middle-scale sites near roadways would 

be eligible for comparison to the annual NAAQS. The EPA’s existing definition of middle-scale for 

PM2.5, 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, encounter 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 situations, 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 corridors or other 

locations in a residential district. In this case, one location 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 few hundred meters such as the 

parking 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 considered “unique.”

EPA and monitoring agencies already have a process for approving PM2.5 monitoring sites as 

described in the Annual Monitoring Network Plan due to the applicable EPA Regional Office by July 1 

of each year (described in 40 CFR 58.10). This existing process provides for identification of sites that 
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are suitable and sites that are not suitable for comparison against the annual PM2.5 NAAQS (§58.10 

(b)(7)). This clarifying language will provide consistency between the PM2.5 design criteria described in 

appendix D to 40 CFR part 58 and the example provided in the special considerations for data 

comparisons to the NAAQS network design (§58.30). Therefore, this clarifying language will help to 

ensure a more consistent identification and approval of sites, and therefore a reduction in burden to 

monitoring agencies and EPA as annual monitoring network plans are prepared, reviewed, public

comments are considered, plans are approved and implemented, and data are ultimately used. in annual 

monitoring network plans that are or are not suitable for comparison to the annual 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 strategy 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)9station 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 improving 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 pollution data from the NCore network can 

 

9 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 

PM2.5 mass and speciation, PM10-2.5 mass, ozone, CO, SO2, NO, NOy, and basic meteorology. 
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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 populated areas, air pollution transported into and outside of a city or region, and air pollution 

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 concentrations 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 PM2.5 NAAQS

In this section, the EPA proposes to add a near-road component to the PM2.5 network design 

criteria and to clarify the use of approved PM2.5 continuous FEMs at SLAMS.

i. Proposed Addition of a Near-road Component to the PM2.5 Monitoring Network

The EPA believes that there are gradients in near-roadway PM2.5 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, the EPA proposes to add a near-road component to the compliance 

network design for PM2.5 monitoring. The EPA believes that by adding a modest number of PM2.5

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 collection of NAAQS comparable 

data in the near-road environment, support for long-term health studies investigating adverse effects on 
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people, providing a better understanding of pollutant gradients impacting neighborhoods that parallel 

major roads, availability of data to validate performance of models simulating near-road dispersion, 

characterization of areas with potentially elevated concentrations and/or poor air quality, implementation 

of a multi-pollutant paradigm as stated in the NO2 NAAQS proposed rule (74 FR 34442, July 15, 2009), 

and monitoring goals consistent with existing objectives noted in the specific design criteria for PM2.5

described in appendix D, 4.7.1(b) to 40 CFR part 58. Near-road PM2.5 sites would also make 

measurement data available for complex locations not routinely monitored currently that may be 

valuable for the implementation of the Agency’s permitting program and transportation conformity 

determinations. 

The monitoring methods that are appropriate for 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 PM2.5 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 PM2.5 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 PM2.5

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 composition by x-ray fluorescence and BC by 

transmissometry. As a result of these tradeoffs, monitoring agencies are encouraged to select one or 

more PM2.5 methods for deployment at near–road monitoring stations that best meet their agencies 

monitoring objectives while ensuring that at least one of those methods is appropriate for comparison to 

the NAAQS (i.e., a FRM, FEM, or ARM). EPA believes that by allowing State monitoring agencies to 

choose the FRM, FEM, or ARM method(s) that best fits their needs, whether filter-based or continuous, 
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that the data will still be able to meet the objectives cited above while ensuring maximum flexibility for 

the States in the operation of their network.

Additionally, the EPA recognizes that the near-road sites would provide a valuable platform for 

evaluating emerging monitoring technologies and for measuring other pollutants besides PM2.5 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, in its response to the 

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 PM2.5 mass measurement. The EPA

also encourages monitoring agencies to explore partnerships with instrument manufacturers and 

researchers to use the sites to evaluate the performance of emerging PM2.5 methods in the near-road 

environment, especially potential or current FEMs able to provide temporally resolved data and capture 

the semi-volatile components of PM2.5. Such emerging PM2.5 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 measure 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. EPA notes that the 

implementation of additional measurements, while encouraged, is completely voluntary to ensure 

maximum flexibility for state monitoring programs. The EPA solicits comment on the best way to 

support such research efforts.
Page 16 of 36

The EPA believes that requiring a modest network of near-road compliance PM2.5 monitors is 

necessary to provide characterization of concentrations in near-road environments. These long-term 

monitors will supplement shorter-term networks operated by researchers to support the tracking of longterm trends of near-road PM2.5 mass concentrations and other pollutants in near-road environments. 

Therefore, the EPA proposes to require near-roadway monitoring of PM2.5 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 PM2.5 concentrations, and a wide range of diverse 

situations with regard to traffic volumes, traffic patterns, roadway designs, terrain/topography, 

meteorology, climate, surrounding land use and population characteristics. Given the latest population 

data available, this proposed requirement would result in approximately 52 required near-road PM2.5

monitors across the country. An indirect benefit of this network 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. 10 While only a single PM2.5 monitor 

is required within each of the CBSAs, agencies may elect to add additional PM2.5 monitoring sites in 

near-road environments. 

While the EPA recognizes that the location of maximum concentration of PM2.5 from roadway 

sources might differ from the maximum location of NO2 or other pollutants, the EPA proposes to require 

that near-road PM2.5 monitors be collocated with the planned NO2 monitors. The NO2 network design 

considers multiple factors that are also relevant for PM2.5 concentrations (e.g., average annual daily 

traffic 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 

 

10 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.
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conjunction with the affected monitoring agencies and the CASAC AAMMS (Russell and Samet, 

2010b) to support deployment. Further, this collocation will allow multiple pollutants to be tracked in 

the near-road environment. Therefore, while there may be limitations to collocating the proposed 52 

near –road PM2.5 monitors with the NO2 stations that will also host CO monitors, on balance, EPA 

believes this is the most efficient and beneficial approach for deployment of this component of the 

network. Thus EPA is seeking to maximize the utility of the network while also reducing the burden on 

monitoring agencies who have already put significant effort into designing their near-road stations for 

NO2 and CO.

EPA notes that the 52 proposed near-road monitors represent a small number of the total 

approximate 900 operating PM2.5 monitoring stations across the country. EPA could consider proposing 

more near-road sites, however, the addition of sites in lower population CBSA’s is not expected to lead 

to much if any difference in characterization of air quality since the bump in PM2.5 concentration

associated with near-road environments in lower population CBSA’s, which typically have

corresponding less travelled roads, is expected to be very small. EPA could also consider proposing 

multiple sites in larger CBSA’s; however, State monitoring programs are already working towards 

representative near-road monitoring stations and there is a synergistic value in ensuring these 

measurements are collocated with multiple measurements to serve the monitoring objectives noted 

above. Since EPA has already finalized requirement of CO monitoring at near-road stations in CBSA’s 

with a population of 1 million or more at sites that are collocated with NO2, there would be less value in 

requiring any more than 52 PM2.5 monitors as any more stations will not have CO for use in multipollutant monitoring objectives (e.g., health studies and model evaluation). Also, EPA wants to ensure 

there is minimal disruption to the existing network and moving more than the proposed 52 PM2.5

monitors may lead to losing some valuable existing PM2.5 stations. Therefore, EPA believes the 52 

proposed near road monitoring stations represent the least burdensome, but most useful number of near-
Page 18 of 36

road monitoring stations to meet the monitoring objectives cited above for deployment across the 

country. 

Ideally, near-road sites would be located at the elevation and distance from the road where 

maximum concentration of PM2.5 occurs in this environment, and within reasonable proximity to an 

area-wide PM2.5 compliance monitoring site at which a similar PM monitor is used (i.e., for comparison 

purposes). Although the EPA is not proposing that the near-road PM2.5 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 

site, such as an NCore station, would provide useful information in characterizing the near-road 

contribution to multiple pollutants, including PM2.5.

The timeline to implement the proposed near-road PM2.5 monitors should be as minimally 

disruptive to on-going operations of monitoring agency programs as possible, while still meeting the 

need to collect for near-road PM2.5 data in a timely fashion. Since the near-road PM2.5 monitors are 

proposed to be collocated with the emerging near-road NO2 network that is scheduled to be operational

by January 1, 2013, the EPA believes it is appropriate to wait until after the near-road NO2 network is 

established before implementing the near-road PM2.5 monitors. Therefore, the EPA proposes that each 

PM2.5 monitor planned for collocation with a near-road NO2 monitoring site be implemented no later 

than January 1, 2015. The EPA believes this proposed deadline provides an appropriate amount of time 

for monitoring agencies to select existing PM2.5 monitors suitable for relocation, receive EPA approval, 

and physically relocate the PM2.5 monitor to the near-road NO2 site. Based on this proposed timeline, 

complete data sets (i.e., 3-years representing 2015-2017), from PM2.5 monitors in the near-road 

environment would be available to calculate site-level design values in 2018.

In summary, the EPA proposes to specifically include a near-road component in the PM2.5

network design criteria for CBSA’s of 1 million persons or greater, with at least one PM2.5 monitor 
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collocated with a near-road NO2 and CO monitors by January 1, 2015. EPA believes that the 52 

proposed PM2.5 monitors to be collocated with NO2 and CO monitors in the near-road environment 

represent the minimal number of sites needed to characterize PM2.5 in representative near road 

environments of large population CBSA’s. EPA believes that a number of PM2.5 monitors can be moved

from single pollutant locations to multi-pollutant locations in the near-road environment, thus 

encouraging efficiencies in operation by monitoring agencies and reducing the burden of continuing to 

support some of the existing single pollutant PM2.5 stations. The EPA solicits comment on this 

approach, especially the proposed network design requirements; any alternative strategies that would 

provide comparable long-term characterization of PM2.5 in area-wide locations of maximum 

concentration in the absence of a specific near-road compliance requirement for monitoring of PM2.5; 

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 collection of supplemental (e.g., non-compliance) measurements 

relevant for the near-road environment.

ii. Use of PM2.5 Continuous FEMs at SLAMS

The EPA proposes that each agency specify their intention to use or not use data from continuous 

PM2.5 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 each 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 PM2.5 FEMs be considered ineligible for 

comparison to the NAAQS. 

In 2006, the EPA finalized new performance criteria for approval of continuous PM2.5 monitors 

as either Class III FEMs or ARMs. The EPA has already approved six PM2.5 continuous FEMs and there 

are nearly 200 of these monitors already operating in State, local, and Tribal networks. Monitoring 

agencies have been deploying and field-testing these units over the last couple of years and the EPA 
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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 VI.D.1.a.iii above, the EPA found that 

some sites with continuous PM2.5 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 use 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 manufacturers, and monitoring agencies to document 

best practices on these methods to improve the comparability and consistency of resulting data wherever 

possible. The EPA believes that the performance of many of these continuous PM2.5 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 PM2.5 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 use 

of data from PM2.5 continuous FEMs in their annual monitoring network plans due to the applicable 

EPA Regional Office by July 1 of each year for any cases where the agency believes that the data 

generated by PM2.5 continuous FEMs in their network should not to be compared to the NAAQS. The 

annual network plans would include assessments such as comparisons of continuous 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 continuous 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 excluded based on an analysis of recent past performance) or a combination of 
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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 PM2.5 data sets used for supporting attainment decisions. However in the first year after 

this proposed option would become effective, we believe it is appropriate to provide monitoring 

agencies with a one-time opportunity to review already reported continuous PM2.5 FEM data and request 

that data with unacceptable performance be restricted (retrospectively) from NAAQS 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 PM2.5 FEM data, as applicable, as well as future data, be restricted from NAAQS 

comparability for the period of time that the plan covers.11 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 PM2.5 continuous FEM that is not 

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 agency 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 available for comparison to the NAAQS. In cases where a PM2.5 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 data 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 

 

11 Data from any PM2.5 monitor being used to meet minimum monitoring requirements could not be 

restricted from NAAQS comparability.
Page 22 of 36

data from PM2.5 continuous 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 PM2.5 NAAQS. Under the current monitoring 

regulations, a monitoring agency can identify a PM2.5 continuous FEM as an SPM, which allows the 

method to be operated for up to 24 months without its data 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 methods whose data are not sufficiently comparable to data from their FRMs. In these 

cases there may be a disincentive to continue operating the PM2.5 continuous FEM, especially in 

networks where the monitoring data is near the level of the NAAQS. With the proposed provision where 

a monitoring agency can recommend not having data from PM2.5 continuous FEMs as comparable to the 

NAAQS, a monitoring agency can continue to operate their PM2.5 continuous FEM to support other 

monitoring objectives (e.g., diurnal characterization of PM2.5, AQI forecasting and reporting), while 

working through options for improved data comparability.

The EPA believes that an assessment of FEM performance should include several elements 

based on the original performance criteria. The Agency also believes that certain modifications to the 

performance criteria are appropriate in recognition of the differences between how monitoring agencies 

operate routine monitors versus 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 those agencies that 

recommend not having data from PM2.5 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 assessment 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 
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practical to utilize the requirement in table C-4 of 40 CFR part 53 for having multiple FRMs and FEMs 

at each 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/m3. 

However, the EPA notes that during an evaluation of data quality from two FEMs (US EPA, 2011a, p. 

4-50), the Agency found that 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/m3) for purposes of evaluating the data 

comparability of continuous FEMs. With regard to the minimum number of samples needed for the 

assessment, the EPA notes 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 sampling 

frequency, two years of data may be necessary to meet this requirement. The EPA recognizes that it 

would be best to assess the data based on the most recently available information; however, having data 

across all seasons in multiple years will provide 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 PM2.5 continuous FEMs as 

comparable to the NAAQS.

The EPA recognizes that only a portion of continuous PM2.5 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 collocated 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 
Page 24 of 36

comparison to the NAAQS. Monitoring agencies may recommend having PM2.5 continuous FEM data 

eligible for comparison to the NAAQS from locations where the method has been demonstrated to 

provide acceptable data comparability, while also recommending 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 

resulting 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 PM2.5 continuous FEM 

that would not meet the expected performance criteria as compared to a collocated FRM. In all cases 

where a monitoring agency chose to group sites for purposes of identifying a subset of PM2.5 continuous 

FEMs that would not be comparable to the NAAQS, the assessment submitted with the annual 

monitoring network plan 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 PM2.5 continuous FEM data should not be compared to the NAAQS, when 

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 PM10-2.5 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 PM10-2.5 speciation be 

conducted at NCore multi-pollutant monitoring stations by January 1, 2011. PM10-2.5 speciation at NCore 

was intended to support further research in the understanding of the chemical composition and sources 

of PM10, PM10-2.5 and PM2.5 at a variety of urban and non-urban NCore locations. Subsequent to the 

completion of the 2006 final monitoring rule, several technical issues were raised concerning the 
Page 25 of 36

readiness of PM10-2.5 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 PM10-2.5 speciation monitoring as part of the current suite of NCore monitoring 

requirements. The requirement to monitor for PM10-2.5 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 PM10-2.5 speciation monitoring, 

a public consultation with the CASAC AAMMS on monitoring issues related to PM10-2.5 speciation was 

held in February 2009 (74 FR 4196, January 23, 2009). At that time, the subcommittee noted the lack of 

consensus on appropriate sampling and analytical methods for PM10-2.5 speciation and expressed concern 

that the Agency’s 2006 commitment to launch the PM10-2.5 monitoring 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 PM10-2.5 speciation monitoring techniques, the Agency did plan and implement a small 

pilot monitoring project to evaluate the available monitoring and analytical technologies and supplement 

the PM10-2.5 speciation measurements that have mostly been done as part of other research efforts. The 

EPA expects that this field study will address the issues needed to develop a more robust, long-term 

PM10-2.5 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, the EPA will consider 

what PM10-2.5 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 
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adequate for PM10-2.5 speciation and that more flexibility in PM10-2.5 speciation network design would 

allow for a geographically diverse network to support health studies and research (Russell, 2009).

The EPA may consider reintroducing some PM10-2.5 speciation 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 PM10-2.5 speciation monitoring 

requirements. The EPA solicits comment on this proposed revision to monitoring requirements.

d. Measurements for the Proposed New PM2.5 Visibility Index NAAQS

The EPA proposes requirements for sampling of PM2.5 chemical speciation in states with large 

CBSAs. The CSN has been operating 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 from these 

existing sites as an input for calculating PM2.5 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 support its existing network objectives while also supporting the 

proposed new secondary PM2.5 visibility index standard (section VI.F), the EPA proposes that each state 

with a CBSA over 1 million have measurements based on the methods in CSN (or IMPROVE), as 

discussed in section VII.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 PM2.5 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 cities 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 
Page 27 of 36

or the proposed population threshold of 2.5 million people. For example, the following 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 PM2.5 visibility index standard. For example, in some cases a large CBSA with 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 requirements and on alternative requirements for CSN 

measurements to support the proposed new secondary PM2.5 visibility index standard.

The EPA proposes that the network design criteria for CSN measurements focus on area-wide 

locations that are generally representative 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 or urban scale of 

representation. The EPA points out that while the existing PM2.5 network design criteria established to 

support the primary PM2.5 NAAQS focuses on the area-wide locations of expected maximum 

concentration, there would not necessarily be the same focus for the proposed new secondary PM2.5

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 the proposed new secondary PM2.5 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 26, 2010). In its letter to the EPA, the CASAC AAMMS stated that “the Subcommittee strongly 
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favored collocation of extinction measurements with PM mass, PM speciation, and precursor gas 

measurements, identifying continuous PM mass and speciation measurements 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 recognized 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” network are 

already well suited for public communications of important vistas.12 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 measurements such as commercially available technologies 

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 with 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 not 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 Assurance Weight of Evidence

 

12 See http://www.hazecam.net/. 
Page 29 of 36

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 interpretations 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 requirements 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 proposes 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-related 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 AQS, data completeness, and 

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 site. 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
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The EPA proposes to include requirements for flow rate verifications and flow rate audits for the 

PM2.5 CSN. These audits are currently being performed so, although they will be considered a new 

requirement, 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 collocate a second set of instruments for speciated 

PM2.5 mass monitoring.

The EPA performed is currently undertaking an assessment13 of measurement uncertainty from 

the collocated CSN and IMPROVE stations using the proposed visibility index and concluded that in 

order to support establishing the current data quality goals for the PM2.5 mass can be achieved for 

chemical 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 PM2.5 Samplers and Monitors

The EPA proposes to allow waivers for the maximum allowable distance associated with 

collocated PM2.5 samplers and monitors. As described in section VIII.A.1 of this proposal, the EPA has 

already approved six Class III PM2.5 continuous FEMs. Several of 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 in 

shelters where they already have gas analyzers operating. Some agencies operate filter-based samplers 

(e.g., PM2.5 FRMs) on top of their shelter, while others operate platforms next to their shelter. In either 

case, ensuring PM2.5 continuous FEMs and PM2.5 FRMs meet collocation requirements (i.e., 1 to 4 

meters for PM2.5 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 sited at the same station.

The EPA believes that maintaining the current requirement of 1 to 4 meters for PM2.5 samplers 

 

13 The assessment is available in Docket number EPA-HQ-OAR-2007-0492, (Papp, 2012)

Formatted: Subscript

Formatted: Normal, Indent: First line: 0.5",

No bullets or numbering
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with flow rates of less than 200 liters/minute is useful since it ensures consistency with long-standing 

practices of collocation and ensures 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, especially 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 PM2.5

and PM10 (US EPA, 1997). In this document, 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 PM2.5 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 PM2.5 samplers and monitors.

5. Proposed Probe and Monitoring Path Siting Criteria 

a. Near-road Component to the PM2.5 Monitoring Network

The EPA proposes that the probe and siting criteria for the near-road component to the PM2.5

monitoring network design follow the same probe and siting criteria as the NO2 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 a 

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 siting criteria for the proposed near-road component to the PM2.5 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 PM2.5 FRMs and FEMs to the CSN measurements. The EPA believes 
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that monitoring agencies are already following the probe and siting criteria for PM2.5 when conducting 

CSN measurements; that is, at neighborhood, urban, and regional scale sites the probe height must be 2 

to 15 meters above ground level. All other aspects of the existing PM2.5 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., greater 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 speciation measurements used to support the proposed new secondary PM2.5 visibility 

index standard.

c. Reinsertion of Table E-1 to Appendix E

The EPA is proposing to reinsert table E-1 to appendix E of 40 CFR part 58. This table presents 

the minimum separation distance between roadways and probes or monitoring paths for monitoring 

neighborhood and urban scale ozone (O3) and oxides of nitrogen (NO, NO2, NOx, NOy). 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 Assessment

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 submitted 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 defined in 

appendix D to 40 CFR part 58, whether new sites are needed, whether existing sites are no longer 
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needed and can be terminated, and whether new technologies are appropriate for incorporation into the 

ambient air monitoring network.14

Since each state has 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 are 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 VII.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 

monitoring zones under the annual monitoring network plans described in 40 CFR 58.10. 

b. Operating Schedules

The EPA generally requires PM2.5 SLAMS to operate on at least a 1-day-in-3 sampling schedule, 

unless a reduced sampling frequency is approved such as might be the case with a site that has a 

collocated continuous operating PM2.5 monitor.15 However, in the 2006 monitoring rule amendments, 

the EPA finalized a new requirement for the operating schedule of PM2.5 SLAMS sites (40 CFR 58.12). 

 

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.

15 All NCore stations must operate on at least a one-in-three day sample frequency for filter-based PM 

sampling.
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The new requirement stated that sites with a design value within plus or minus five percent of the 

24-hour PM2.5 NAAQS must have an FRM or FEM operating on a daily sampling schedule. This 

requirement was included to minimize any statistical error associated with the form of the 24-hour PM2.5

NAAQS (i.e., the 98th percentile). In section III.F, the Administrator is proposing to revise the level of 

the primary annual PM2.5 NAAQS. Accordingly, she is now considering whether this 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 51354, 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 2006. 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 PM2.5 NAAQS and the known burden 

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 PM2.5 standard should be reconsidered if the site already has a design value above the 

level of the primary annual PM2.5 NAAQS. 

In a related issue, since the EPA finalized the requirement for daily sampling at sites within 5 

percent of the 24-hour PM2.5 NAAQS in 2006, there has been confusion 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 PM2.5 NAAQS and the site has a design value that is not above the 

level of the annual PM2.5 NAAQS. (2) The EPA proposes that review of data for purposes of 

determining applicability of this requirement at a minimum be included in each agency’s annual 
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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 deadline. 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 comment on these proposed changes to the required 

operating schedule for PM2.5 SLAMS.

c. Data Reporting and Certification for CSN and IMPROVE Data

The EPA solicits 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 its 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 with 

sites that are not NCore (note: all NCore stations use either IMPROVE or the 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 reporting and certification16 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 proposed PM2.5 visibility 

index values discussed in section VII.A.5 above. Since 2010, the EPA has required states to certify their 

 

16 Data certification requirements are described in 40 CFR 58.15. 
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data by May 1 of each year. Since in some cases chemical speciation data may not be fully validated and 

submitted to EPA by May 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 for archival of PM2.5, PM10, and PM10-2.5 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 

filters 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 

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 proposes 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 require cold storage 

during the first year.