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**UNITED STATES ENVIRONMENTAL PROTECTION AGENCY**

**WASHINGTON D.C. 20460**

August 26, 2008

EPA-CASAC-08-020

**OFFICE OF THE ADMINISTRATOR**

**SCIENCE ADVISORY BOARD**

The Honorable Stephen L. Johnson

Administrator

U.S. Environmental Protection Agency

1200 Pennsylvania Avenue, N.W.

Washington, D.C. 20460

Subject: CASAC Ambient Air Monitoring & Methods (AAMM) Subcommittee Peer
Review of the Draft Federal Reference Method (FRM) for Lead in PM~10~

Dear Administrator Johnson:

EPA's Office of Air Quality Planning and Standards (OAQPS), within the
Office of Air and Radiation, requested that the Agency's Clean Air
Scientific Advisory Committee (CASAC) Ambient Air Monitoring & Methods
(AAMM) Subcommittee (CASAC Subcommittee) conduct a peer review of EPA's
"Draft Federal Reference Method (FRM) Lead in PM~10~ (Pb-PM~10~)"
---that is, lead (Pb) in particulate matter less than 10 micrometers in
diameter (PM~10~) --- dated June 15, 2008. The CASAC Subcommittee roster
is enclosed as Enclosure A to this letter, Subcommittee members'
individual written comments are found in Enclosure B, and the Agency's
background and charge memorandum to the Subcommittee is provided in
Enclosure C.

The Agency solicited CASAC's advice on this topic as part of EPA's
current review of the National Ambient Air Quality Standards (NAAQS) for
Lead. Several options being considered for the final Lead NAAQS would
require the Agency to develop FRM and Federal Equivalent Method (FEM)
criteria for the collection of Pb-PM~10~ in ambient air, in order for
monitoring data to be used in determining attainment with the NAAQS. The
Agency has proposed a FRM for Pb-PM~10~ based on the existing,
low-volume PM~10c~ sampler (*i.e.*, a PM~10~ sampler that meets special
requirements that are part of a PM~10-2.5~ reference method sampler, as
specified by Federal regulation), coupled with analysis by the x-ray
fluorescence (XRF) analytical method.

The Agency released its Proposed Rule for the Revision of the NAAQS for
Lead (40 CFR Parts 50, 51, 53 & 58) on May 1, 2008, and this was
subsequently published in the *Federal Register* on May 20, 2008 (73 FR
29184--29291) as a Notice of Proposed Rulemaking (NPR). On July 14,
2008, the CASAC Subcommittee Number range CHAPTERNumber range
CHAPTERconducted its review of the proposed FRM for the measurement of
Pb-PM~10~ via a public advisory teleconference. The statutory
(chartered) CASAC held a subsequent public teleconference meeting on
August 18, 2008 to discuss and approve the draft letter (dated August
11, 2008) containing our comments and recommendations.

EPA specifically requested the Subcommittee's comments both regarding
the type of sampler to be used and the choice of the multi-elemental
analytical method for the Pb-PM~10~ FRM --- and, in particular, the
low-volume PM~10c~ FRM sampler and the XRF analysis method,
respectively. The CASAC Subcommittee notes that the range of the level
for the revised Lead NAAQS under consideration in this NPR is quite
broad, extending from 0.1 to 0.5 μg/m^3^. The Subcommittee was therefore
challenged in this peer review by not having a narrower "target" range
for the final NAAQS for Lead, since the level and averaging time of the
revised Lead standard significantly impact the suitability of candidate
sampling and analytical methods. Without more guidance on EPA's data
quality objectives (DQOs) for Lead monitoring, the members of the CASAC
Subcommittee are unable to provide definitive responses to Questions 2
and 4 that Agency staff posed to the Subcommittee as part of its review.

Nevertheless, overall --- and subject to addressing the CASAC's
previously-expressed concerns with transitioning to a Pb-PM~10~ sampling
indicator (reiterated below) --- *the CASAC Subcommittee unanimously
supports the use of the PM~10c~ FRM sampler*. In addition, *it is the
consensus recommendation of the Subcommittee in this peer review that
EPA consider selecting inductively coupled plasma--mass spectroscopy
(ICP-MS) as the Pb-PM~10~ FRM analytical method* *and using XRF as an
FEM*.

The five charge questions from the Agency, along with a synthesis of the
CASAC Subcommittee's responses, are found immediately below:

1.  *What are your comments on the use of the low-volume PM~10c~ FRM
    sampler as the Pb-PM~10~ FRM sampler?*

If the EPA chooses to transition from a lead in total suspended
particulate (Pb-TSP) sampling indicator to a Pb-PM~10~ indicator, the
CASAC Subcommittee is generally supportive of using the PM~10c~ FRM
sampler. The rationale for such a selection is well laid-out in the
draft FRM document that the Agency presented to the CASAC Subcommittee
for its peer review, as well as in the individual written comments from
Subcommittee members. However, as discussed below, the CASAC has
previously noted that the choice of Pb-PM~10~ as a sampling indicator
should be conditional on a considerable tightening of the final Lead
standard.

2.  *What are your comments on the use of XRF as the Pb-PM~10~ FRM
    analysis method?*

By way of background, on March 25, 2008, the CASAC Subcommittee held a
public advisory teleconference meeting to conduct a consultation with
OAQPS on several ambient air monitoring issues related to the Lead
NAAQS, including issues associated with alternative lead indicators. As
is the CASAC's customary practice, there was no consensus report from
the CASAC as a result of that consultative meeting. However,
Subcommittee members' individual written comments were attached in
Appendix B of the CASAC's letter to the Agency (EPA-CASAC-08-010, dated
April 14, 2008). A majority of the Subcommittee members who submitted
individual written comments pursuant to this March 25 consultation
generally indicated that XRF was an appropriate Pb-PM~10~ FRM analysis
method, although several members commented that the Agency should
consider using ICP-MS (or, in one case, atomic-absorption (AA)
spectroscopy) as an alternate analytical method for the FRM.

In addition, as mentioned above in this letter, this question is
particularly difficult to answer without a clearer sense of the level of
the revised NAAQS for Lead. Moreover, at present, the CASAC Subcommittee
is unsure as to what the analytical requirements are for this method, as
well as the Agency's associated data quality objectives. The
Subcommittee understands that an analysis of the DQOs is underway ---
albeit in the face of uncertainty concerning both the level and the
averaging time of the revised Lead NAAQS.

That having been said, the CASAC Subcommittee considers XRF as
possessing a number of potential benefits over competing approaches,
although it also has some weaknesses. Specifically, XRF is, overall,
viewed positively by the Subcommittee, in that it: is reasonably
cost-effective; is currently being used for analysis of the Speciation
Trends Network (STN) filters; provides concentrations of elements other
than lead; avoids the extraction procedures required by methods such as
ICP-MS and AA spectroscopy; and is non-destructive. On the other hand,
in comparison with XRF, ICP-MS offers lower detection limits, more
direct calibration against NIST-traceable references, transparent
interpretation of results, and compatibility with the fiber filters used
for high-volume TSP or PM~10~ measurements. Importantly, the uniformity
of sample deposits across the face of low-volume PM~10c~ filters would
need to be more carefully investigated prior to selection of an XRF FRM,
because XRF analyzes only a portion of the filter. The use of in-line
filter holders appears to exacerbate this problem, and it is noted that
some XRF methods (*e.g.*, the PANalytical instrument) slowly rotate the
analysis holder during analysis, which allows the oval-shaped x-ray beam
to scan over a much larger area, thus minimizing bias if there is any
inhomogeneity of the filter deposit. Nonetheless, with whole-filter
extraction methods such as ICP-MS, the uniformity of the deposit is no
longer an issue, although completeness of recovery of lead from the
filter for ICP-MS analysis must still be confirmed.

On balance, therefore, the issues of deposit uniformity and calibration
standards associated with XRF raise analytical concerns not found with
ICP-MS with respect to EPA's accuracy goal of "an upper 95 percent
confidence limit for the absolute bias of 10 percent." *Accordingly, the
CASAC Subcommittee recommends that the Agency consider selecting ICP-MS
as the FRM and using XRF as an FEM.*

3.  *What are your comments on the specific analysis details of the XRF
    analysis method contained in the proposed Pb-PM~10~ FRM analysis
    method description?*

Whether XRF is used as the FRM or as an FEM, there are a number of
issues that need to be addressed more thoroughly than currently appears
in the Agency's draft FRM for Pb-PM~10~, in that the appropriate section
of EPA's review document should be oriented more towards providing
specific details for the analysis of airborne lead. Whatever analytical
method is used laboratory and field blanks should be used to detect
possible contamination in the filters and the overall system. It is
recognized that different lots of filters may have dissimilar blank
levels, so filters should be matched with blanks from the same lots. A
relatively large number of laboratory blanks should be analyzed in each
lot. Furthermore, field blanks, comprising approximately ten percent
(10%) of all sample filters, should be deployed and analyzed as well.

4.  *Do you think the precision, bias and MDL of the XRF method for the
    proposed Pb range will be adequate?*

Again, answering this question is sensitive to the choice of the form
and level of the revised NAAQS for Lead, as implied by the question
itself, and is made more difficult by not having DQOs available for the
CASAC Subcommittee's review. The Subcommittee understands that there has
been limited time to develop the DQOs, and that the Agency is also
disadvantaged by having such a broad range for the level of the final
Lead NAAQS under consideration, as well as the possible change in the
averaging time of the standard. As discussed above, *XRF is a viable
method, and should be able to meet the bias and method detection limit
(MDL) requirements. However, the lack of uniformity in the deposition of
lead on filters could pose issues with meeting the precision
requirements*. Accordingly, EPA should confirm that for the sampler
being used, non-uniformity in the deposition of lead particles does not
compromise meeting the specified DQOs. Given its greater sensitivity,
and concerns over the non-uniformity of deposition impacting XRF
results, a number of individuals on the Subcommittee specifically
recommend that ICP-MS be selected as the analysis method for the FRM.

5.  *Are there any method interferences that we have not considered?*

In the judgment of the CASAC Subcommittee the Agency has adequately
identified the potential interferences with XRF.

Finally, the CASAC, in its letter dated January 22, 2008
(EPA-CASAC-08-007), had recommended transitioning the sampling indicator
for lead from TSP to a low-volume ambient air monitor for Pb-PM~10~.
This transition to a new indicator was also supported by a majority of
the members of the CASAC AAMM Subcommittee during its March 25, 2008
consultative teleconference (see EPA-CASAC-08-010). Notwithstanding, as
discussed in the most recent letter from the CASAC (EPA-CASAC-08-016,
dated July 18, 2008), the discussion leading up to this recommendation
assumed a significant tightening of the lead NAAQS. In particular, as
the CASAC noted in its July 18 letter, a Lead NAAQS set at a level as
high as 0.5 μg/m^3^, using a Pb-PM~10~ sampling indicator, could
potentially allow TSP Pb levels as high as 1 μg/m^3^ at sites near large
sources with coarse-mode particulate lead emissions. Therefore, the
CASAC clarified its recommendation by stating that, if the level of the
revised lead NAAQS approaches this upper end of the range, the current
TSP indicator should *not* be changed --- adding that, while
transitioning from a Pb-TSP to a Pb-PM~10~ sampling indicator would
indeed be "preferable," this change should only be effected if the level
of the final NAAQS for Lead is established "conservatively below an
upper bound of 0.2 μg/m^3^ or lower."

In closing, the CASAC Subcommittee welcomes the opportunity to review
EPA's proposed FRM for Pb-PM~10~, and reiterates that the choice of an
appropriate FRM is crucial with respect to the timely development of a
more health-protective Lead NAAQS. The Subcommittee stands ready to
provide additional advice and recommendations with respect to any
air-quality

monitoring issues, especially those related to the NAAQS. As always, we
wish the Agency well in these important efforts to protect both human
health and the environment.

> Sincerely,

***/Signed/ /Signed/***

Dr. Armistead (Ted) Russell, Chair Dr. Rogene F. Henderson, Chair

CASAC AAMM Subcommittee Clean Air Scientific Advisory Committee

Enclosures

**NOTICE**

> This report has been written as part of the activities of the EPA's
> Clean Air Scientific Advisory Committee (CASAC), a Federal advisory
> committee independently chartered to provide extramural scientific
> information and advice to the Administrator and other officials of the
> EPA. The CASAC provides balanced, expert assessment of scientific
> matters related to issues and problems facing the Agency. This report
> has not been reviewed for approval by the Agency and, hence, the
> contents of this report do not necessarily represent the views and
> policies of the EPA, nor of other agencies within the Executive Branch
> of the Federal government. In addition, any mention of trade names or
> commercial products does not constitute a recommendation for use.
> CASAC reports are posted on the EPA Web site at:
> [[http://www.epa.gov/casac]{.underline}](http://www.epa.gov/casac_).

**Enclosure A -- Roster of the CASAC Ambient Air Monitoring & Methods
(AAMM) Subcommittee**

Number range CHAPTER**U.S. Environmental Protection Agency**

**Clean Air Scientific Advisory Committee (CASAC)**

**CASAC Ambient Air Monitoring & Methods (AAMM) Subcommittee**

**CASAC MEMBERS**

**Dr. Armistead (Ted) Russell (Chair)**, Georgia Power Distinguished
Professor of Environmental Engineering, Environmental Engineering Group,
School of Civil and Environmental Engineering, Georgia Institute of
Technology, Atlanta, GA

**Dr. Ellis Cowling,** University Distinguished Professor At-Large,
Emeritus, Colleges of Natural Resources and Agriculture and Life
Sciences, North Carolina State University, Raleigh, NC

**Dr. Donna Kenski**, Director of Data Analysis, Lake Michigan Air
Directors Consortium (LADCO), Rosemont, IL

**SUBCOMMITTEE MEMBERS**

**Mr. George Allen**, Senior Scientist, Northeast States for Coordinated
Air Use Management (NESCAUM), Boston, MA

**Dr. Judith Chow**, Research Professor, Desert Research Institute, Air
Resources Laboratory, University of Nevada, Reno, NV

**Mr. Bart Croes**, Chief, Research Division, California Air Resources
Board, Sacramento, CA

**Dr. Kenneth Demerjian**, Professor and Director, Atmospheric Sciences
Research Center, State University of New York, Albany, NY

**Dr. Delbert Eatough**, Professor of Chemistry, Emeritus, Chemistry and
Biochemistry Department, Brigham Young University, Provo, UT

**Mr. Eric Edgerton**, President, Atmospheric Research & Analysis, Inc.,
Cary, NC

**Mr. Henry (Dirk) Felton**, Research Scientist, Division of Air
Resources, Bureau of Air Quality Surveillance, New York State Department
of Environmental Conservation, Albany, NY

**Dr. Philip Hopke**, Bayard D. Clarkson Distinguished Professor,
Department of Chemical Engineering, Clarkson University, Potsdam, NY

**Dr. Rudolf Husar**, Professor, Mechanical Engineering, Engineering and
Applied Science, Washington University, St. Louis, MO

**Dr. Kazuhiko Ito**, Assistant Professor, Environmental Medicine,
School of Medicine, New York University, Tuxedo, NY

**Dr. Thomas Lumley**,\* Associate Professor, Biostatistics, School of
Public Health and Community Medicine, University of Washington, Seattle,
WA

**Dr. Peter McMurry**, Professor, Department of Mechanical Engineering,
Institute of Technology, University of Minnesota, Minneapolis, MN

**Mr. Richard L. Poirot**, Environmental Analyst, Air Pollution Control
Division, Department of Environmental Conservation, Vermont Agency of
Natural Resources, Waterbury, VT

**Dr. Kimberly Prather**,\* Professor, Department of Chemistry and
Biochemistry, University of California, San Diego, La Jolla, CA

**Dr. Jay Turner**, Visiting Professor, Crocker Nuclear Laboratory,
University of California - Davis, Davis, CA

**Dr. Warren H. White**, Research Professor, Crocker Nuclear Laboratory,
University of California - Davis, Davis, CA

**Dr. Yousheng Zeng**, Air Quality Services Director, Providence
Engineering & Environmental Group LLC, Providence Engineering and
Environmental Group LLC, Baton Rouge, LA

**Dr. Barbara Zielinska**, Research Professor, Division of Atmospheric
Science, Desert Research Institute, Reno, NV

**SCIENCE ADVISORY BOARD STAFF**

**Mr. Fred Butterfield**, Designated Federal Officer, 1200 Pennsylvania
Avenue, N.W., Washington, DC, 20460, Phone: 202-343-9994, Fax:
202-233-0643
([[butterfield.fred@epa.gov]{.underline}](mailto:butterfield.fred@epa.gov))
(Physical/Courier/FedEx Address: Fred A. Butterfield, III, EPA Science
Advisory Board Staff Office (Mail Code 1400F), Woodies Building, 1025 F
Street, N.W., Room 3604, Washington, DC 20004, Telephone: 202-343-9994)

\*Dr. Lumley and Dr. Prather did not participate in this CASAC AAMM
Subcommittee activity.

**Enclosure B -- Comments from Individual CASAC**

**AAMM Subcommittee Members**

> This appendix contains the written comments of individual members of
> the Clean Air Scientific Advisory Committee (CASAC) Ambient Air
> Monitoring & Methods (AAMM) Subcommittee. The comments are included
> here to provide both a full perspective and a range of individual
> views expressed by Subcommittee members during the review process.
> These comments do not represent the views of the CASAC AAMM
> Subcommittee, the CASAC, the EPA Science Advisory Board, or the EPA
> itself. Subcommittee members providing written comments are listed on
> the next page, and their individual comments follow.

**[Panelist]{.underline} [Page \#]{.underline}**

Mr. George Allen
........................................................................................B-3

Dr. Judith
Chow\..........................................................................................
B-5

Mr. Bart
Croes\.............................................................................................
B-21

Dr. Kenneth
Demerjian..................................................................................B-23

Dr. Delbert
Eatough..................................................................................\.....B-25

Mr. Dirk Felton
..........................................................................................
B-26

Dr. Philip
Hopke..........................................................................................
B-29

Dr. Kazuhiko Ito
.........................................................................................
B-30

Dr. Donna Kenski
.......................................................................................
B-32

Dr. Peter
McMurry..................................................................................\...\...
B-33

Mr. Richard
Poirot..................................................................................\...\....B-35

Dr. Jay
Turner..................................................................................\...\...\...\.....
B-38

Dr. Warren H. White
....................................................................................B-40

Dr. Yousheng Zeng
......................................................................................B-44

Dr. Barbara
Zielinska....................................................................................B-45

**Mr. George Allen**

The following are written comments based on the Charge Questions in the
EPA OAQPS memo to the SAB dated June 15, 2008. These comments also
reflect discussion during the July 14 teleconference AAMM meeting on a
peer review of the Draft Federal Reference Method (FRM) Lead in PM10
(Pb-PM10). A copy of these comments is also being sent to Dr. Ted
Russell, CASAC AAMM Subcommittee Chair.

Peer Review Charge Questions in **Bold**:

**1. What are your comments on the use of the low-volume PMl0c FRM
sampler as the Pb-PM10 FRM sampler?**

The existing PM10c sampler is an obvious choice for a sampler since it
is well characterized and commercially available from several vendors.
Sequential (automated) PM10 samplers should also be allowed, either as
FRM or FEM samplers. The dichotomous sampler is another obvious
candidate for an FRM or FEM sampler for PM-10 lead.

**2. What are your comments on the use of XRF as the Pb-PM10 FRM
analysis method?**

XRF is sufficient for routine analysis, but for the FRM, a more
sensitive and specific technique should be used, such as ICPMS. If XRF
is used, the method should be an FEM. If XRF remains the FRM analysis
method, there are concerns of uniform deposit on the filter that may
differ with different sizes (coarse vs. fine mode) of particles.
Appropriate filter deposition testing would have to be done prior to
promulgation of XRF as the FRM analysis method. There are also concerns
regarding different XRF analytical methods and calibration techniques
across different laboratories, the lack of a NIST thin-film XRF Pb
reference standard, possible issues with heavy filter loading, the
difficulty of generating spiked samples, and the possibility of
interferences. ICPMS does not have any of these concerns.

**3. What are your comments on the specific analysis details of the XRF
analysis method contained in the proposed Pb-PM10 FRM analysis method
description?**

The XRF analysis method description proposed here is well written and
takes into account most of the issues raised above. It does not resolve
the issues of non-uniform deposition or the lack of a NIST thin-film
standard for Pb. A PM10 filter can appear visually to have a uniform
deposit, but in urban areas the visual appearance is often driven by
fine-mode aerosol which may not reflect the deposition pattern of coarse
mode Pb. Thus, visual inspection is only a crude first test for uniform
deposition of PM-10 Pb. The issue of filter blanks needs more attention;
blank values can vary by manufacturing lot. Thus, the blanks used for a
set of samples must be from the same lot. The method description does
not use field blanks; it is important to have 5% of filters used as
field blanks. The method needs to include a section on how levels below
the method's LOD or LOQ will be handled. I suggest reporting the
blank-corrected data as measured (even if it is slightly negative), but
flagging it as below the LOD.

**4. Do you think the precision, bias and MDL of the XRF method for the
proposed Pb range will be adequate?**

The XRF MDL for Pb will be a function of XRF method and blank levels and
variability. Although the MDL noted in this method description (1 ng/m3
one-sigma) is adequate, it may or may not be achieved in the real world,
since the MDL is a function of many things, including the number and
stability of lab and field blank filters and the length of XRF analysis
time. The bias and method detection limits in this draft are
appropriate. I would suggest that the FEM precision be tightened from
15% to 10%.

**5. Are there any method interferences that we have not considered?**

Not that I am aware of.

**Dr. Judith Chow**

This memo addresses the twelve questions on which the Subcommittee
members were asked to comment regarding Attachment 1, "Draft Federal
Reference Method (FRM) for Lead in PM~10~ (Pb-PM~10~), and Attachment 2,
"Approaches for the Development of a Low-Volume Ambient Air Monitor for
Lead in Total Suspended Particulate (Pb-TSP) Sampler." This supplements
prior comments to the first set of questions that was appended to the
April 14, 2008 letter from Dr. Russell to Administrator Johnson.

# Questions for Attachment 1 \[Draft Federal Reference Method (FRM) for Lead in PM10 (Pb-PM~10~)\]

## Question 1: What are your comments on the use of the low-volume PM~10c~ FRM sampler as the Pb-PM~10~ FRM sampler? {#question-1-what-are-your-comments-on-the-use-of-the-low-volume-pm10c-frm-sampler-as-the-pb-pm10-frm-sampler .Style-Heading-2-+-Before:--2.4-pt-After:--2.4-pt}

My prior comments in the April 14 letter recommended that EPA move
toward Pb-PM~10~. These comments pointed out the lack of specificity and
variability of inlet characteristics for the high-volume TSP sampler
(Code of Federal Regulations, 2007a). High-volume TSP is a poor
surrogate for inhalable particles and a poor surrogate for deposited
particles. A true "Total Suspended Particulate" sampler that collects
all of particles that remain in the air is of such large dimensions that
it requires a small trailer and a large power supply to operate (Burton
and Lundgren, 1987; Lundgren et al., 1984). The argument given in favor
of retaining TSP in the April 14 letter was that large particles could
contaminate surface areas and soils that might be ingested or
resuspended. If toxic soils and house dust are of concern in addition to
inhalable PM~10~, then these should be sampled and analyzed directly
(Egami et al., 1989; Adgate et al., 1998; Farfel et al., 2001; Bai et
al., 2003).

FRM sampler inlets have been wind-tunnel tested and have well-defined
cut-points and slopes (10.2 ± 1.41 µm for SA-246B inlet; Watson and
Chow, 1993; 2001). Sampling systems coupled with these inlets provide
accurate flow control, use low trace metal background PTFE
Teflon-membrane filters, and yield precise mass measurements when
coupled with appropriate laboratory weighing procedures. Low-volume
PM~10c~ FRMs (Appendix O to Part 50) are similar to PM~2.5~ FRMs, which
use the same PM~10~ impactor inlet with the addition of WINS or very
sharp-cut cyclone inlets (Kenny et al., 2000; 2004; Peters et al.,
2001a; 2001b; 2001c). The low-volume PM~10c~ FRM sampler is consistent
with EPA's proposed difference method for PM~10-2.5~ (U.S.EPA, 2006)
that uses identical filter media, sample collection, gravimetric
analysis, and quality assurance \[QA\]/quality control \[QC\])
procedures for the side-by-side samplers.

Low-volume PM~10~ and PM~2.5~ samplers are commercially available, are
widely deployed in many urban networks, and network operators are
familiar with them. Costs for additional sampling and analysis should be
reasonable. There is no need for a separate Pb-PM~10~ network, although
the existing low-volume PM~10~ network might be expanded to suspected Pb
hot-spots, as recommended by several committee members in the April 14
letter. The Pb-PM~10~ network should be considered within the context of
EPA's integrated air monitoring strategy (Scheffe et al., 2007; U.S.EPA,
2005) that intends to re-design the national monitoring system to attain
multiple objectives beyond compliance (Chow and Watson, 2008).

## Question 2: What are your comments on the use of XRF as the Pb-PM~10~ FRM analysis method? {#question-2-what-are-your-comments-on-the-use-of-xrf-as-the-pb-pm10-frm-analysis-method .Style-Heading-2-+-No-underline-Before:--3-pt-After:--3-pt}

Energy dispersive x-ray fluorescence spectroscopy (XRF; NIOSH, 1998;
U.S.EPA, 1999a; Watson et al., 1999a; RTI, 2004; DRI, 2007) is the most
commonly used analytical method for multi-elemental analysis on
Teflon-membrane filter samples, and the protocols always include Pb. XRF
does not destroy the sample, so it can be archived and re-examined for
stable particles by other methods (volatile aerosol components such as
ammonium nitrate evaporate in XRF's evacuated sample chamber). XRF is
currently used for PM~2.5~ elemental analysis at urban locations in the
Chemical Speciation Network (CSN), at non-urban locations in the
Interagency Monitoring of PROtected Visual Environments (IMPROVE)
network, and in many special studies.

Other methods have been proven to be equally sensitive, accurate, and
precise for Pb measurements, including Proton Induced X-ray Emission
Spectroscopy (U.S.EPA, 1999b), Atomic Absorption Spectroscopy (AAS) Code
(Fernandez, 1989; NIOSH, 1994a; 1994b; U.S.EPA, 1999c; Code of Federal
Regulations, 2007b), Inductively-Coupled Plasma Atomic Emission
Spectroscopy (ICP-AES; U.S.EPA, 1999d; NIOSH, 2003a; 2003b; 2003c),
Inductively-Coupled Plasma Mass Spectrometry (ICP-MS), and Anodic
Stripping Voltametry (ASV; NIOSH, 2003d). These methods are commonly
applied to air filters for Pb, especially in workplace environments and
Hazardous Air Pollutant (HAPs) networks.

With adequate standard operating procedures (SOPs; such as those cited
above), these methods give comparable results for a wide range of sample
types and environments (Keppler et al., 1970; Gilfrich et al., 1973;
Camp et al., 1974; 1978; Ahlberg and Adams, 1978; Nottrodt et al., 1978;
Witz et al., 1982; Lin et al., 1993; Walder and Furuta, 1993; Pyle et
al., 1996; Bettinelli et al., 1997; Reynolds et al., 1997; Watson et
al., 1997; 1999b; 2000; Lemieux et al., 1998; Ashley et al., 1999; Rich
et al., 1999; VanCott et al., 1999; Gigante and Gonsior, 2000; Sterling
et al., 2000; Farfel et al., 2001; Harper et al., 2002; 2004; 2005;
2006; 2007; Menzel et al., 2002; Sussell and Ashley, 2002; Bai et al.,
2003; Drake et al., 2003; Moreira et al., 2005; Ariola et al., 2006;
Harper and Pacolay, 2006; Harris et al., 2006; Herner et al., 2006;
Kilbride et al., 2006; Kim et al., 2007).

Figure 1 shows an example comparing Pb concentrations measured by AAS on
high-volume PM~10~ quartz-fiber filter analyzed by the Illinois
Department of Environmental Quality with Pb by XRF on the summed fine
and coarse Teflon-membrane filters from a collocated dichotomous sampler
analyzed by DRI. The results are comparable, with a few outliers. These
monitors from South Chicago were in a highly industrialized area with
relatively high levels of arsenic (As), selenium (Se) and other
potentially toxic elements. Refined Pb is amenable to a common acid
extraction method, such as nitric acid and aqua regia, which is not the
case for most minerals (and possibly not for Pb in its native ore prior
to refining). The comparisons for other toxic elements in Watson et al.
(2000) are not as good as those for Pb.

Although a method may be shown to yield quantities comparable with
reference materials and analyses by other methods, it may be inadequate
if the equipment and procedures are not up to the task. Each SOP should
state its assumptions and include tests to indicate when deviations from
those assumptions are excessive. The procedure should attempt to
minimize the effects of interferences or sample deviations from the
ideal. The ability of an XRF procedure to attain a 1 ng/m^3^ Pb
detection limit depends on the filter mass (which affects the background
count), sample volume, sample duration, and deposit area. It also
depends on the Pb excitation radiation energy, intensity, beam area, and
analysis time. The sensitivity and resolution of the SiLi detector is an
important consideration, as well as peak overlap that will raise the
background (which decreases the analysis precision). There are
different, but analogous, considerations for the other methods cited
above.

![](media/image2.wmf){width="6.499305555555556in"
height="4.185416666666667in"}

**Figure 1.** Comparison of PM10 lead concentrations from an Andersen
high-volume PM~10~ on QMA quartz-fiber filters analyzed by AAS and a
Sierra 241 dichotomous PM~10~/PM~2.5~ sampler with Teflon-membrane
filters analyzed by XRF (Watson et al., 1999a) at the four sites during
the third year of the Robbins Particulate Study in South Chicago between
10/01/97 and 09/26/98 (Watson et al., 2000).

As long as the minimum detectable limits (MDLs; 1.5 ng/cm^2^), precision
(±15% at 90% confidence level), and accuracy (±5%) are within the EPA's
specified levels, any of the methods cited above should be adequate.
That said, XRF and/or proton induced x-ray emission (PIXE) can
simultaneously acquire 40-50 elements without much additional cost
(except for the cost of acquiring additional standards, performing
instrument calibration, and data processing). If only Pb is desired,
most of the multi-element excitation conditions can be dropped, thereby
increasing throughput and further lowering costs. The issues of
extraction efficiency, use of different acid mixtures for extraction,
matrix interferences, potential contamination, and sample destruction
inherent in AAS, ICP-AES, ICP-MS, and ASV result in these methods being
more costly, but they may be of use in some instances. For example,
ICP-MS can quantify Pb isotopic abundances that might be of use in
quantifying source contributions (Munksgaard and Parry, 1998).

## Question 3. What are your comments on the specific analysis details of the XRF analysis method contained in the proposed Pb-PM~10~ FRM analysis method description? {#question-3.-what-are-your-comments-on-the-specific-analysis-details-of-the-xrf-analysis-method-contained-in-the-proposed-pb-pm10-frm-analysis-method-description .Style-Heading-2-+-Before:--2.4-pt-After:--2.4-pt}

While the method description in Appendix Q to Part 50, "Reference Method
for the Determination of Lead in Particulate Matter as PM~10~ Collected
From Ambient Air" covers many details, there are several points that
need clarification:

[Section 1.1 (Line 2).]{.underline} PM~10~ should be collected on an
"acceptance tested" 46.2 mm diameter polytetrafluoroethylene (PTFE)
filter. Acceptance testing is performed to verify blank levels for
Teflon-membrane filters. In the early 1970s, one batch of
Teflon-membrane filters was contaminated with Pb from the manufacturer,
and this compromised the study results (Chow, 1995a).

[Section 1.1 (Lines 7 and 8).]{.underline} The definition of PM~10~
should include a specific inlet efficiency curve with a 50% cut-point
and slope, similar to the PM~10~ FRM specification (U.S.EPA, 1987).

[Section 1.4 (Line 1).]{.underline} Is it necessary to specify
"electrically powered"? I don't see any problem with other vacuum
assisted suction methods as long as the flow rate specifications are
attained. Photovoltaic cells and batteries are also sources of
electricity.

[Section 1.4 (Line 8).]{.underline} Change "Line intensity" to "photon
energy".

[Section 2.1 (Line 3).]{.underline} The deposit area on ringed
Teflon-membrane filters varies slightly from different speciation
samplers (e.g., 11.76 -- 11.78 cm^2^), and it is smaller than the 11.86
cm^2^ estimated for the Pb-PM~10~ FRM sampler. It would be better if the
deposit area is measured from several samplers and sample batches to
assure that the correct value is being used.

[Section 2.2 (Lines 4-5).]{.underline} "The one-sigma detection limit
for Pb is calculated as the average overall uncertainty or propagated
error for Pb, determined from measurements on a series of blank
filters." This should be more explicit, i.e., translate the square root
of the number of counts from a series of blank filters near the Pb
analysis energies into µg/m^3^ using the XRF calibration factor
(µg/count), sample volume, and deposit area. The one-sigma detection
limit is best based on each batch of unexposed blank filters to account
for batch-to-batch variations. Even though these variations are expected
to be small, it is a better practice to ensure consistency among
different batches of filters. This might be incorporated into the
acceptance testing criteria.

[Section 3.1 (Lines 1 and 3).]{.underline} Define "too much deposit"
(Line 1) and "heavy deposit" (Line 3). This shouldn't be a problem with
XRF, because Pb has a strong energy and is not much affected by particle
size or sample deposit (Criss and Birks, 1968; Hunter and Rhodes, 1972;
Rhodes and Hunter, 1972; Dzubay and Nelson, 1975; Adams and Billiet,
1976). One could require a calculation of self-adsorption and the
loading at which it might exceed the measurement tolerances using one or
more of the cited methods.

[Section 3.1 (Line 5).]{.underline} While an optimum PM~10~ filter
loading of 150 µg/cm^2^ or 1.6 mg/filter is reasonable for a 46.2 mm
filter with a low-volume (16.7 L/min) sampler, this value needs to be
justified with a citation. The same is true for the minimum deposit of
15 µg/cm^2^ (Line 7). An optimal loading estimate might be required to
be part of the procedures, again using published formulae.

[Section 3.1 (Lines 8-10).]{.underline} Deposit non-uniformity may occur
if an in-line filter holder is used, but in-line filter holders are not
part of PM~10~ low-volume samplers. The deposits are very uniform with
these samplers, as evidenced by their appearance. Modern XRF equipment
also rotates the sample, and the incident beam is at an off-center
angle, thereby lessening the effects of a non-uniform deposit. Deposit
uniformity might be defined by a performance specification of some kind
and be addressed in the SOP.

[Section 3.2 (Line 11).]{.underline} "Energy resolution" should be
defined as \< 155-160 eV full-width at half maximum..

[Section 4.1 (Line 4).]{.underline} A CV of 15% is high. Typically,
precision can be much better than ±10%.

[Section 6.1.2. (Lines 4-5).]{.underline} Selecting 50 out of 500
filters, or 10% of blank filters, for acceptance testing is more than is
needed. Two filters out of a hundred are more reasonable and
cost-effective.

[Section 6.1.2 (Line 8).]{.underline} Where did 4.8 ng Pb/cm^2^ come
from? Based on the past records, 1-3 ng Pb/cm^2^ seems to be a more
adequate acceptance level, but this needs to be validated with a
citation.

[Section 6.2.1 (Lines 2 and 3).]{.underline} The method should not imply
that Thermo and PANalytical, are the only units. UC Davis designed and
operates its own system for IMPROVE samples, and it seems to work fine.
I believe EPA is still using the old LBL workhorse in its RTP labs.
Xenemetrix (new owners of Jordan Valley, www.xenemetrix.com/index.htm)
and Spectro (www.spectro.com/pages/e/index.htm) also have XRF units
adaptable to this purpose.

[Section 6.2.2 (Lines 1-4).]{.underline} Both 15 and 50 µg/cm^2^ Pb thin
film standards can be obtained from Micromatter Inc. (Arlington, WA).
NIST (2008) also has a Pb standard solution, standard reference material
(SRM) 3128 with certified Pb value of 9.987 ± 0.018 mg/g, or other SRMs
in different matrices that might be applicable to assessing accuracy and
precision.

[Section 6.2.4 (Line 17).]{.underline} "Calibration is performed only
when significant repairs occur or when a change in fluorescers, X-ray
tubes, or detector is made." Most XRFs are robust and may not need
repairs for years. QA standards with each run monitor intensities and
peak separations. Nevertheless, it's a good idea to perform base
calibrations at least once per year, and to use the L~β~ line as a
secondary peak to verify Pb by the L~α~ line.

[Section 6.2.4.2 (Lines 3-4).]{.underline} Rather than keeping 20-30
filters as clean blank filters, it is better to retain 2% of every new
batch of filters (i.e., 100 per batch) for acceptance testing (see above
comment on Section 6.1.2).

## Question 4. Do you think the precision, bias and MDL of the XRF method for the proposed Pb range will be adequate? {#question-4.-do-you-think-the-precision-bias-and-mdl-of-the-xrf-method-for-the-proposed-pb-range-will-be-adequate .Style-Heading-2-+-Before:--2.4-pt-After:--2.4-pt}

Yes, with the appropriate samples and procedures. Arsenic (As) and other
spectral interferences can be estimated and corrected, and this is
commonly done using the Pb L~β~ as well as the Pb L~α~ to quantify Pb
levels. A quick calculation shows that if As levels were so high as to
overwhelm the Pb lines, then Pb exposure would not be the biggest
problem. The deposit inhomogeneity reported by Bandhu et al. (2000) was
caused by their use of in-line filter holders. Chow (1995b) shows
pictures of samples from in-line filter holders, demonstrating that you
don't need a lot of analysis to know when the deposit is non-uniform.
The aerosol sampler (Fitz et al., 1989) used in the Southern California
Air Quality Study (SCAQS) used in-line filter holders and required some
extra effort to adjust the elemental data (Cahill et al., 1989; Chow et
al., 1994; Matsumura and Cahill, 1991) for subsequent interpretation.
None of the samplers under consideration use in-line filter holders, and
all of them have a long-enough transition zone to assure a uniform
deposit. The good comparability reported in most of the studies cited
above could not be achieved if this were not the case.

## Question 5. Are there any method interferences that we have not considered? {#question-5.-are-there-any-method-interferences-that-we-have-not-considered .Style-Heading-2-+-Before:--2.4-pt-After:--2.4-pt}

XRF spectrum processing methods are well-established for thin samples,
and most of the newer analyzers have software that can implement several
of the most common approaches to background subtraction, peak overlap
correction, self-absorption (not really needed for Pb), coincidence
counting, and deadtime corrections. The software implements
well-established and non-proprietary methods (Bonner et al., 1973;
Dzubay et al., 1977; Giauque et al., 1977; Grennfelt et al., 1971;
Lubecki, 1969; Parkes et al., 1974; Russ, 1977; Statham, 1976; Statham,
1977) that can be applied to any digitized spectrum.

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**Mr. Bart Croes**

Overall, the documents provided to the Subcommittee continue the
impressive responsiveness by U.S. EPA staff to CASAC and our
Subcommittee's comments. Staff should be commended for taking a
systematic approach towards implementation of a likely revised lead (Pb)
National Ambient Air Quality Standard (NAAQS). I appreciate the
opportunity to comment during several stages of the process, and agree
with the basic approach taken by U.S. EPA. My comments address the
consultation questions posed by Lewis Weinstock in his June 15, 2008
memo to Fred Butterfield. These comments also reflect input from
California Air Resources Board (ARB) staff responsible for implementing
U.S. EPA monitoring requirements and using the data in source
apportionment and health studies.

### Charge Questions:

Attachment 1 -- Draft Federal Reference Method (FRM) Lead in PM10
(Pb-PM10)

1.  *What are your comments on the use of the low-volume PM~l0c~ FRM
    sampler as the Pb‑PM~10~ FRM sampler?*

> Replacing the current, high volume FRM with a low volume sampler based
> on PM10c and PM2.5 FRMs is desirable for the following reasons:

-   Low volume sampling offers advantages in pressure/temperature flow
    correction for sample collection in local (actual) conditions.

-   Low volume samplers have solid state electronic controls and data
    logging while high volume samplers utilize mechanical timers and
    have no data logging capability,

-   Low volume samplers offer the opportunity for remote operation and
    data access where high volume samplers do not.

-   Quartz and glass fiber filters used in high volume sampling have far
    higher background levels of Pb than Teflon filters used in low
    volume sampling.

> Leaving the door open to potential FEMs is desired.  For example, the
> ARB Toxics network (Xontech 924, low volume TSP, Teflon filter,
> ICP-MS) may or may not be equivalent, but California should have the
> opportunity to find out.

2.  *What are your comments on the use of XRF as the Pb-PM~10~ FRM
    analysis method?*

> While it has problems with non-uniform deposits, XRF provides an
> efficient method of analysis and requires less sample preparation than
> other analytical methods.  The other species will also allow source
> apportionment.

3.  *What are your comments on the specific analysis details of the XRF
    analysis method contained in the proposed Pb-PM~10~ FRM analysis
    method description?*

    The description as written was adequate.

4.  *Do you think the precision, bias and MDL of the XRF method for the
    proposed Pb range will be adequate?*

> The MDL for Pb is well below 0.001 μg/m^3^ (looking at California
> data) for a 24-hour sample, so there should be no problem with
> determining compliance for the new standard.  Most of the lead samples
> at the (very clean) IMPROVE sites are valid.
>
> Using IMPROVE XRF as an example, here are data from the Agua Tibia
> site, north of Escondido in northern San Diego County. The scatterplot
> of reported uncertainty vs. concentration shows good performance
> across the range of concentrations reported, with most concentrations
> in the well-quantified zone.
>
> The vertical lines denote (left to right):\
> - The mean reported MDL.\
> - Warren White\'s \"Rule of Thumb\" MQL (10 x MDL).
>
> \- The proposed new standard (0.2 μg/m^3^).\
> - The old standard (1.5 μg/m^3^).\
> ![](media/image3.jpeg){width="6.496527777777778in"
> height="4.586805555555555in"}
>
> Based on this quick look, commercial XRF systems are capable of very
> good quantification near the proposed new standard.

5.  *Are there any method interferences that we have not considered?*

> Not to my knowledge.

**Dr. Kenneth Demerjian**

**Comments regarding monitoring methods for the measurement of PM lead
in the atmospheric re: Draft Federal Reference Method (FRM) for Lead in
Pb-PM10**

1.  **What are your comments on the use of the low-volume PMl0c FRM
    sampler as the Pb-PM10 FRM sampler?**

The application of the PM10c FRM sampler is an acceptable approach for
the monitoring of lead. It leaves open the possibility of missing Pb
exposure from PM-Pb \> 10 μm diameter particles. Measuring the
concentration of PM-Pb as a function of particle size at a select number
of representative monitoring sites would address this size cut issue and
the data would likely be informative to the health community as well.

**2. What are your comments on the use of XRF as the Pb-PM10 FRM
analysis method?**

I do not agree with this choice. I recommend that ICP-MS be the FRM for
the analysis of Pb and that XRF be considered as a FEM. The ICP-MS has
better overall quality assurance and quality control (QA/QC) and
traceable standards than the XRF method. In addition, the extraction and
digestion of Pb compounds in ICP-MS analyses has proven to be quite
effective and efficient (Qureshi, et al., 2006).

Among the issues raised regarding XRF, the uniformity of material on the
filter collection surface and the potential role of large particle
contributions to this non homogeneity remain of greatest concern. It
would seem prudent to study these issues prior to formally committing to
a decision on sampler type and the performance requirements of the
analytical methods. The fact that the TSP Pb measurement has been of
historical poor quality in terms of particle size sampling, should not
be used as a rationalization that any incremental improvement in PM-Pb
monitoring is better than the status quo.

**3. What are your comments on the specific analysis & details of the
XRF analysis method contained in the proposed Pb-PM10 FRM analysis
method description?**

An effort should be made to archive and test filter blanks by batch
number.

**4. Do you think the precision, bias and MDL of the XRF method for the
proposed Pb range will be adequate?**

The approach described is adequate for characterizing the performance of
the XRF analysis for Pb under ideal filter sample collection. It is
clear from discussions among committee members that significant
uncertainties remain with regard to XRF's quantification. These include
potential effects of sampling inlets, Pb particle size and the
uniformity of collected PM on the filter. D. Felton's comments, present
data which indicate the extreme sensitivity in precision and accuracy
with respect to ambient Pb concentration levels and certainly makes the
case for the need to reconsider the statistical measures for precision
and accuracy for the low Pb concentrations typical observed in urban
areas (e.g. figure 1 below)

> ![](media/image4.png){width="4.514583333333333in"
> height="3.2881944444444446in"}

**5. Are there any method interferences that we have not considered?**

All standard sources of interference have been identified. The low
levels ambient PM Pb in the atmosphere will continue to be a challenge
and require maintaining filter blank quality and monitoring the
integrity of sample handling and potential contamination sources within
the sample collection system.

Qureshi, S., V. A. Dutkiewicz, K. Swami, K. X. Yang, L. Husain, J. J.
Schwab, and K. L. Demerjian, 2006. Elemental Composition of PM2.5
Aerosols in Queens, New York: Solubility and Temporal trends,
Atmospheric Environment, 40, S238-S251.

**Dr. Delbert Eatough**

[Comments on Draft Federal Reference Method (FRM) for Lead in
Pb-PM~10~]{.underline}

**What are your comments on the use of the low-volume PM~l0c~ FRM
sampler as the Pb-PM~10~ FRM sampler?**

I fully support the suggestion. The sampler is well characterized,
available and compatible with other instruments in existing networks.
For reasons stated in Section 2., I do not believe that basing the
standard on a low volume TSP sampler is a good idea at this time.

**What are your comments on the use of XRF as the Pb-PM~10~ FRM analysis
method?**

I am not an expert on XRF but concur with the points made by others that
the establishment of ICP-MS as the FRM with XRF as a FEM is a reasonable
direction to go. The reasons given for going this direction as discussed
in the call included: 1) Availability of the technique in many states;
2) Ease of extraction and sensitivity of analysis for the techniques;
and 3) Avoidance of the issues inherent with XRF if the deposit on the
filter is not uniform.

**What are your comments on the specific analysis & details of the XRF
analysis method contained in the proposed Pb-PM~10~ FRM analysis method
description?**

**Do you think the precision, bias and MDL of the XRF method for the
proposed Pb range will be adequate?**

**Are there any method interferences that we have not considered?**

As I am not an expert on XRF analysis, I defer to the comments made by
members of the committee who are.

**Mr. Dirk Felton**

***Peer Review* of the Draft Federal Reference Method (FRM) for
Pb-PM10**: **Attachment 1 - Draft Federal Reference Method (FRM) Lead in
PM-10 (Pb-PM10)**

[Background and Summary:]{.underline} In order for monitoring data to be
used in determination of attainment with the NAAQS, the data must be
collected with a FRM or FEM. A number of options under consideration for
the Pb NAAQS indicator would require the EPA to develop a FRM and FEM
criteria for the measurement of Pb in PM~10~. The EPA has proposed
language for a FRM for Pb- PM~10~ based on the existing FRM sampler for
low volume PM~10c~ in Appendix O to Part 50 of the Code of Federal
Regulations (CFR) coupled with analysis by x-ray fluorescence (XRF). The
attached document includes the proposed regulatory text for the FRM for
Pb in PM~10~.

[Charge Questions:]{.underline}

*What are your comments on the use of the low-volume PM~10c~ FRM sampler
as the Pb-PM~10~ FRM sampler?*

> The PM~10c~ sampler is adequate for use as the Pb-PM~10~ FRM sampler.
> Many States already use this sampler for NATTS PM~10~ metals sampling.
> Number range CHAPTERThe sequential versions of the samplers should
> also be designated as FRMs because future Pb PM~10~ FEM evaluations
> should use the FRM samplers and protocols most predominantly utilized
> in the national network. Future FEM evaluations should be designed
> with the identical sample collection interval (midnight to midnight)
> and filter handling procedures as followed by the majority of the data
> providers for the national network.

*What are your comments on the use of XRF as the Pb-PM~10~ FRM analysis
method?*

> Number range CHAPTERSpecifying XRF would make analytical problems
> stemming from non-uniform loading, spectral overlap and non-ideal
> filter loading densities an inherent part of the FRM. ICPMS should be
> the analysis method for the FRM and for the PEP audit samples. ICPMS
> is more accurate and it does not require the filter to be uniformly
> loaded. XRF should be designated as a cost effective FEM that is
> routinely compared to ICPMS through the periodic collocation of the
> PEP audit program.
>
> It should also be noted that gravimetric mass determination of the
> sample filter is not required for Pb analysis.

*What are your comments on the specific analysis details of the XRF
analysis method contained in the proposed Pb-PM~10~ FRM analysis method
description?*

> The section on background measurement and correction states that
> 20--30 clean blank filters are kept in a sealed container and are used
> exclusively for background measurement and correction. These should be
> replaced with filters that are representative of the "batches" of
> filters that are used for the current measurements. It is likely that
> filter qualities such as thickness, density and contaminant
> concentrations will change over time.

*Do you think the precision, bias and MDL of the XRF method for the
proposed Pb range will be adequate?*

> XRF is not the most accurate method for use in a Pb FRM and if
> selected it should be viewed as a compromise between cost
> effectiveness and accuracy at concentrations below about 0.01 µg
> Pb/m^3^. For low concentration measurements, it is preferable to use
> ICPMS which is more accurate and does not require the filter to be
> uniformly loaded for the FRM. XRF should be designated as an FEM and
> be permitted for use unless accuracy at very low concentrations is
> necessary for specific monitoring objectives.
>
> The MDL for Pb XRF as stated in the draft Reference Method is 0.001
> μg/m^3^. At this concentration the Pb data is not accurate enough to
> be used reliably for anything other than to demonstrate that the
> amount of Pb in the air is low. The EPA should consider establishing a
> minimum reporting level for XRF Pb no lower than 0.005 μg/m^3^. Levels
> below this can be reported but flagged as between detection limit and
> reporting limit or set to zero if they are below 0.001 μg/m^3^.
>
> The draft PM~10~ method references the procedures in Appendix A, Part
> 58 for use in precision calculations. CFR Appendix A, Part 58 (1997 --
> section 5.3.1.1) states that the concentrations of both collocated
> pairs of Pb data must be above 0.15 ug/m^3^ in order for the data to
> be used in precision calculations. This concentration will be too high
> for most of the sites in the new Pb monitoring network. A lower value
> can be selected but the precision of the measurement will decrease
> rapidly at lower concentrations. In Figure 1 below, STN PM~2.5~ Pb is
> compared to data from a collocated PM~2.5~ FRM in which the filters
> were analyzed for Pb by XRF. This data should emulate what we would
> expect to see for the precision calculations for a clean site in the
> proposed low volume PM~10~ Pb network. As we can see, the Percent
> Difference rapidly increases below about 0.02 µg Pb/m^3^. This is only
> one example but it serves to demonstrate that the proposed method's
> precision determination will have to account for XRF's increase in
> error at low concentrations.
>
> The EPA may have to revise the way statistics are calculated for Pb or
> other NAAQS developed in the future for individual components of PM.
> The typical ambient concentrations of Pb are of course much lower than
> those for gravimetric mass and are closer to instrument and method
> detection limits. The statistics used to determine precision and
> accuracy may have to be specified as a range; looser at low
> concentrations where much of the ambient data will be and tighter at
> higher concentrations closer to the Pb NAAQS.

![](media/image5.wmf){width="4.874305555555556in"
height="3.1055555555555556in"}

*Are there any method interferences that we have not considered?*

> The sampler components and the shipping and handling materials for the
> filter samples must be free of Pb that can affect the integrity of the
> sample. The metal used to produce the sampler inlet is of particular
> concern and there should be a specified limit for the amount of trace
> Pb that is permissible for any component of the sampler including
> o-rings and greases. It would also be advisable to restrict the use of
> brass upstream of the sample filter or in any part that experiences
> wear and is exposed to the sampler exhaust such as in cooling fans and
> motor brushes.

**Dr. Philip Hopke**

A stumbling block for the development of a new sampler from "scratch" is
what are the criteria that would be desired in such a sampler. My
suggestion is that if we are concerned about a combination of inhaled
risk including deposition in the head airways that would result in
transport to the GI tract as well as hand-to-mouth behavior, then we
should look at developing a sampler that would meet the "inhalable"
curve defined by industrial hygienists. Figure 1 presents the
penetration curves for the typical PM size fractions.

> ![](media/image6.wmf){width="5.0in" height="3.9090277777777778in"}

Clearly such development would take some time so I would suggest as
multi-pronged approach. There are at least three commercially available
low-volume TSP heads currently on the market (Thermo, BGI, and URG).
These could be tested by Dr. Kenny in the UK or there are wind tunnels
at universities where sufficient testing is possible even it if does not
fully meet 40 CFR 58 requirements. Depending on the outcome of these
tests, it might be possible to denote one or more of these as
sufficiently close to the IPM curve to move ahead with these. If none of
the heads provide adequate response characteristics, then an effort can
be initiated to design an inlet that meets the established criteria.

It should be noted that any TSP head is going to be sensitive to wind
speed. They are cylindrically symmetric and thus, wind direction
invariant.

**Dr. Kazuhiko Ito**

**[General Comment]{.underline}**:

I understand that, because of the schedule for the proposed new FRM for
Pb-PM~10~, we are asked specific charge questions at this point.
However, based on the conversations that took place during the July
14^th^ conference call, it seems to me that there are some important
uncertainties that need to be investigated or characterized further even
after the new method and alternative low-volume TSP samplers are
considered. Specifically, as Dr. Hopke pointed out, it seems unclear if
the Pb-PM~10~ (or perhaps even Pb-TSP) is the most appropriate indicator
of Pb exposure if the relevant route of exposure is ingestion of surface
deposited Pb.

**[Charge Questions and comments:]{.underline}**

**• Attachment 1 Draft Federal Reference Method (FRM) Lead in PM~10~
(Pb-PM~10~)**

***What are your comments on the use of the low-volume PM~10c~ FRM
sampler as the Pb-PM~10~ FRM sampler?***

To the extent that we are interested in Pb in PM~10~ size fraction, the
PM~10c~ sampler is acceptable and appropriate for Pb-PM~10~ FRM, given
the performance shown in the past tests.

***What are your comments on the use of XRF as the Pb-PM~10~ FRM
analysis method?***

I imagine the information on the issues associated with Pb analysis by
XRF is available from the nationwide PM~2.5~ speciation data collected
since 2000. Analysis of such data would be informative.

***What are your comments on the specific analysis details of the XRF
analysis method contained in the proposed* *Pb-PM~10~* *FRM analysis
method description?***

The document describes potential spectral interferences and spectral
overlaps, but it does not give us a sense of the extent of this problem
in the real data. It would be helpful if the document could also
describe likely extent of this issue. Again, how serious a problem was
this in the nationwide PM~2.5~ chemical speciation data?

***Do you think the precision, bias and MDL of the XRF method for the
proposed Pb range will be adequate?***

I think this answer depends on the extent of spatial variation of
Pb-PM~10~ in the locations of interest as well as the actual NAAQS level
for Pb. The goal for a 15% precision for co-located monitors may be
adequate if a coefficient of variation of annual means for multiple
monitors within an area of interest is, say, 50%, but this would vary
from city to city. I happened to look at within-city variation of
several PM~2.5~ chemical species including Pb in 28 MSAs several years
ago for a different reason (I was comparing within-city vs. across-city
variation of PM components). Figure 1 shows the coefficient of variation
(CV) for the across-MSA variation vs. distributions of CV's of
within-MSA variation for the 28 MSAs where there were multiple monitors
for years 2000--2003. For Pb, the CV ranges from nearly zero to 60% with
the median of \~ 25%. Therefore, the adequacy of precision of 15% may be
OK for the cities where high Pb levels occur (I imagine Pb-PM~10~
variation would be larger than that for Pb-PM~2.5~).

![](media/image7.jpeg){width="5.125in" height="3.2222222222222223in"}

**Figure 1.** Comparison of coefficient of variation (C.V.) of annual
(multi-year, '00-'03) means across MSAs (denoted with bold "-") and
distribution of within-MSA C.V. of annual means in the 28 MSAs where
multiple monitors were available. "o" represents extreme value.

***Are there any method interferences that we have not considered?***

I don't know of any.

**Dr. Donna Kenski**

**Comments on the Peer Review for Pb NAAQS**

**1. What are your comments on the use of the low-volume PM~l0c~ FRM
sampler as the Pb‑PM~10~ FRM sampler?**

The PM~10c~ FRM sampler is the obvious and best choice for a Pb-PM~10~
FRM sampler.

**2. What are your comments on the use of XRF as the Pb-PM~10~ FRM
analysis method?**

I don't see the logic in selecting XRF over ICP/MS as the analysis
method. ICP/MS is more sensitive and not subject to the interferences
that are documented in Joann Rice's memo. NIST-traceable standards can
be used for calibration and many states have in-house labs that can
perform the analysis. And, it does not require uniform filter loading.
XRF is perfectly suitable for an FEM, but I recommend that ICP/MS be
selected as the FRM analytical method.

**3. What are your comments on the specific analysis details of the XRF
analysis method contained in the proposed Pb-PM~10~ FRM analysis method
description?**

The description as written was adequate.

**4. Do you think the precision, bias and MDL of the XRF method for the
proposed Pb range will be adequate?**

The MDL as specified is fine if determination of compliance with the
NAAQS is the only issue. But since health professionals, EPA, and others
have a valid interest in determining concentrations at levels far below
the NAAQS, it seems shortsighted not to measure Pb with higher accuracy
at the (more common) low concentrations as well. With the (presumed)
lowering of the Pb NAAQS, and with generally lower ambient
concentrations across the country, the MDL should be lower than the
0.001 µg Pb/m^3^ that is proposed. As this is easily achievable and
already being accomplished by other national networks, it ought to be
part of the FRM method.

5.  **Are there any method interferences that we have not considered?**

Not that I know.

**Dr. Peter McMurry**

Comments regarding measurement methods for particulate lead in
atmospheric aerosols ---[Comments on Draft Federal Reference Method
(FRM) for Lead in Pb-PM~10~]{.underline}

**What are your comments on the use of the low-volume PM~l0c~ FRM
sampler as the Pb-PM~10~ FRM sampler ?**

I think it is a good idea. This sampler is readily available, is
familiar to monitoring agencies, and has been well-tested. Furthermore,
the Pb samples would be sampled in the same way as PM~10~ mass, so the
fraction of mass that is Pb would be well defined.

**What are your comments on the use of XRF as the Pb-PM~10~ FRM analysis
method?**

Chemical analysis is not my primary area of expertise. Therefore, the
views expressed here represent my synthesis of comments from today's
telephone conversation.

I think very compelling arguments were made to use an extraction method
such as ICP-MS rather than XRF as the FRM analysis method. These include
the (1) the confidence that Pb can be effectively extracted with
efficiencies that approach 100%, (2) the availability of NIST traceable
standards for liquid solutions of Pb that can be used to calibrate
analytical instruments used to analyze dissolved extracts and the
corresponding lack of such standards for deposited Pb, (3) the
availability of instruments, such as ICP-MS in states and the
corresponding unavailability of XRF instruments, (4) the sensitivity of
XRF to spatial distributions of deposits on filters, which are unlikely
to be uniform (especially for coarse particles) and the corresponding
insensitivity of extraction methods to such non-uniformities, (5) the
use of proprietary software for analyzing XRF data, which shields the
public from a clear understanding of how concentrations of lead are
determined, and (6) the superior sensitivity of methods such as ICP-MS.
I question whether XRF would meet the accuracy and precision goals
required for a standard.

Because XRF is inexpensive and nondestructive, I think it makes sense to
use it as a FEM.

**What are your comments on the specific analysis & details of the XRF
analysis method contained in the proposed Pb-PM~10~ FRM analysis method
description?**

I will defer to other members on the committee on this.

**Do you think the precision, bias and MDL of the XRF method for the
proposed Pb range will be adequate?**

Again, I will defer to those members of the committee who are more
knowledgeable than I on this topic. I was left with the sense there are
compelling arguments for using another analytical method as the FRM.

**Are there any method interferences that we have not considered?**

Not to my knowledge.

**Mr. Richard Poirot**

**Comments on Proposed Pb PM~10~ FRM - Appendix Q Part 50**

An important prefacing comment is that the CASAC Lead Panel has
advocated a transition of the Pb indicator from TSP to PM~10~ Pb if,
[and only if]{.underline}, the level of the standard is set lower than
0.2 µg/m^3^. If a level equal to or higher than 0.2 µg/m^3^ is selected,
the CASAC Pb panel is unanimously opposed to a reduction in the
indicator particle size range from TSP to PM~10~.

***What are your comments on the use of the low-volume PM~10c~ FRM
sampler as the Pb-PM~10~ FRM sampler ?***

Assuming the level of the Pb standard is set below 0.2 µg/m^3^, the
PM~10c~ sampler would be an appropriate choice for a Pb-PM~10~ FRM
sampler.

***What are your comments on the use of XRF as the Pb-PM~10~ FRM
analysis method?***

XRF should be an adequate analytical method for a Pb NAAQS set toward
the middle to upper end of the range of levels recommended by EPA staff
and the CASAC Pb Panel. If the level is set toward the low end of that
recommended range (0.02 µg/m^3^), a more accurate analytical method like
ICP-MS, with lower detection limits and smaller analytical errors, would
be preferable. Consideration should also be given to specifying ICP-MS
as the FRM and establishing XRF as a FEM.

***What are your comments on the specific analysis & details of the XRF
analysis method contained in the proposed Pb-PM~10~ FRM analysis method
description?***

I think it should be useful and possible to tighten up some of the
specific details relating specifically to the determination of Pb by
EDXRF. Much of the description sounds more like cautionary guidance
rather than prescribed details of specific procedures, and also seems to
pertain to XRF analysis of elemental species other than Pb. This raises
a related point that it would be best to be very clear up-front about
analytical and data reporting procedures for (readily detectable) XRF
elements other than Pb that may result at little or no extra cost from
the Pb XRF analysis (and would also represent an important reason in
favor of the choice of XRF as part of the Pb FRM). Arguably this
"supplemental data" would have value for quality assurance and source
attribution of the Pb measurements, and if significant additional costs
are not incurred, analytical and data reporting procedures could be
specified. Similar considerations would also apply if (multi-elemental)
ICP-MS were selected as the Pb FRM. Along similar lines, clear guidance
should also be provided on whether (or not) there should be PM~10~ mass
measurements conducted on the Pb FRM filters. Possibly the Agency would
want to provide for an optional national analytical contractor, as has
proved effective for IMPROVE and STN networks. Alternatively, some
consideration should be also given to coordination with the evolving
NAATS metals sampling program which generally (but not always) utilizes
PM~10c~ samplers combined with ICP-MS analyses (at most but not all
sites), and which would benefit from greater internal consistency.

***Do you think the precision, bias and MDL of the XRF method for the
proposed Pb range will be adequate?***

The precision, bias and MDL of the XRF method should be adequate for a
Pb NAAQS in the currently proposed range of 0.1 to 0.3 µg/m^3^, although
a PM~10~ sampling method is not recommended if the level is greater than
or equal to 0.2 µg/m^3^. The XRF precision, bias and MDL could pose
problems for a NAAQS set at the lower end of the EPA staff-recommended
range of 0.02, and may result in uncertainties in spatial patterns and
temporal trends at population-oriented monitoring sites where levels are
likely to fall well below the proposed NAAQS range. The indicated XRF
PM~10~ Pb MDL of 0.001 µg/m^3^ would be only 1% of the lower bound level
of the proposed NAAQS and unlikely to have a significant influence on
compliance determinations. I also think it's likely that this MDL could
be further reduced. For example the current MDL for PM~2.5~ Pb in the
IMPROVE network is closer to 0.0001 µg/m^3^.

Current Pb precision comparisons are limited to concentrations above 10%
of the current NAAQS (i.e., 0.15 µg/m^3^). This limit will need to be
lowered to reflect the hopefully much lower level of the currently
revised NAAQS. Also, since it generally appears likely that the
Administrator may select a level (and form) of the standard which are
less stringent than are warranted by the Agency's Risk/Exposure
Assessment and Staff Paper, some consideration should be given to
collection of accurate and precise data at levels below and possibly
well below the level of the NAAQS selected in this review cycle.

**Are there any method interferences that we have not considered?**

None that I'm aware of -- related to XRF analysis of Pb on PM~10C~
filters. However, it should be recognized that XRF is not very well
suited for analysis of fiberglass TSP or hi-volume Quartz PM~10~
filters. ICP-MS would be a better choice for an FRM analytical method
that could be used across all potential filter types, and would provide
a better basis for comparative sampling to develop better information on
Pb particle size distributions, sources etc. --- especially in the event
that TSP (and/or hi-vol PM~10~) are retained (or specified as FEM).

**Other minor comments on Pb PM~10~ FRM:**

p\. 3, para 1, line 6: The hyphenated "24-hour sample" is correct here,
but all other instances of the number "24" in this document are also
(incorrectly) attached by hyphen to the words that follow. These include
"24-hours" in line 3 and "24-cubic meters" in line 5 of this paragraph
and 2 instances of "24-m^3^" in 2^nd^ and 3^rd^ paragraphs on page 5.

p\. 6, para 1: You present optimal (150 µg/cm^2^) and minimal (15
µg/cm^2^) PM~10~ mass loading levels (roughly 75 and 7.5 µg/m^3^
respectively) for XRF Pb quantification, but also indicate potential
distortion with "unusually heavy deposits". Why not also provide the
PM~10~ mass level that would be considered unusually heavy (i.e. an
upper bound to go along with the ideal and minimal loading levels).
Also, unless mass measurements are required, how will it be known
whether the filter loading is above, below or within the range where
distortion-free measurements are expected?

p\. 6, para 2, line 3: You could add "S/P" to this list of XRF
interferences.

p\. 7, para 2, line 6: This effect is "especially significant and more
complex for PM~10~ measurements..." than for what?

p\. 8, section 6.1.2, last line: Just for curiosity, what is the basis
for your selection of this blank Pb limit of 4.8 ng/cm^2^? This (x 11.86
cm^2^ of exposed filter / 24 m^3^ of air sampled) would yield an implied
ambient Pb concentration of 0.002 µg/m^3^ --- or about twice the
indicated Pb XRF MDL - or about 1% of a standard of 0.2 µg/m^3^ (are you
giving us a hint about the intended level of the NAAQS?).

p\. 9, section 6.2.3, line 2: What do you mean "Filters are typically
archived in cold storage"? For what current analyses is this cold
storage procedure "typical"? Will it be required for Pb sampling? What
elements, if any, which are quantifiable by XRF do you expect to see
volatized from filters if they are not kept in cold storage prior to
analysis? Certainly you don't expect any loss of Pb, do you?

**Dr. Jay Turner**

**Peer Review: Draft Federal Reference Method (FRM) Lead in PM~10~
(Pb-PM~10~)**

[Charge Questions]{.underline}

1.  *What are your comments on the use of the low-volume PM~10c~ FRM
    sampler as the Pb-PM~10~ FRM sampler?* The low-volume PM~10c~ FRM
    sampler is an appropriate choice as the Pb-PM~10~ FRM sampler. It is
    an adaptation of the PM~2.5~ FRM sampler which now has nearly ten
    years of use and refinement, including both single-event and
    sequential configurations. There are also operational and cost
    advantages to placing measurements for multiple NAAQS on the same
    sampler platform. For sites specified for both PM~10~ and Pb-PM~10~
    compliance monitoring, filter samples collected using the low-volume
    PM~10c~ FRM sampler could be subjected to both gravimetric analysis
    and Pb elemental analysis, providing compliance data for both
    standards from a single sample.

2.  *What are your comments on the use of XRF as the Pb-PM~10~ FRM
    analysis method?* I prefer the use of ICPMS (or GFAAS) as the FRM
    with an expectation that XRF would be given FEM status. While ICPMS
    does have the added complexity of a sample digestion step, it can be
    more easily calibrated than XRF. Our recent experience with ICPMS
    has demonstrated high recovery for both coal fly ash and urban
    particulate matter NIST Standard Reference Materials (SRM) from
    quartz filters using a nitric acid and hydrochloric acid extraction
    solution (following the NATTS PM~10~ metals sampling and analysis
    protocol developed by ERG). The Pb-PM~10~ method would use Teflon
    filters and ERG has also developed a protocol for this case which
    could be used as a starting point for the analysis method
    specifications.[^1]

3.  *What are your comments on the specific analysis details of the XRF
    analysis method contained in the proposed Pb-PM~10~ FRM analysis
    method description?* I defer to the XRF experts for a critique of
    the analysis method details. Given the variations in instrument
    hardware and software, all labs reporting compliance data based on
    XRF should participate in an audit program which includes analyses
    of samples with traceability to ICPMS.

4.  *Do you think the precision, bias and MDL of the XRF method for the
    proposed Pb range will be adequate?* These questions are best
    addressed after completion of the DQO process. Perhaps the required
    MDL could be relaxed depending on the NAAQS concentration value,
    although a detection limit that is much lower than the standard is
    desirable to simplify the data handling for concentrations below
    the MDL. Precision should be determined using data with Pb
    concentrations above a defined threshold value since the precision
    reported as a percentage CV will degrade as the MDL is approached.
    In general, we should be prepared for both ICPMS and XRF data being
    reported to AQS, and these methods will have very different
    detection limits. This will add complexity to certain non-compliance
    data analyses; including trends analyses studies on Pb health
    effects.

5.  *Are there any method interferences that we have not considered?* I
    defer to the XRF experts on the issue of method interferences.

    **Dr. Warren H. White**

COMMENTS ON PROPOSED FRM FOR PM10 LEAD ---

[Use of low-volume PM~10c~ FRM sampler]{.underline}

As noted in our previous consultation, the uniformity of this sampler's
collected deposit needs to be established if XRF is used as the
analytical method. Attachment 1 illustrates the need for such a
determination with an example of a non-uniform sample collected with a
different (non FRM) sampler. The elements Pb and Fe, presumed associated
with different particle size classes, show quite different deposition
patterns in this example. As the x-ray beam fluoresces only the central
portion of the filter, the ratio of reported loading to ambient
concentration varies accordingly.

XRF analysis of filters from this sampler would thus respond differently
to fine Pb particles from fume sources and coarse Pb particles from dust
sources.

[XRF as method of analysis]{.underline}

XRF is cost-effective, is sensitive enough for the levels under NAAQS
consideration (see below), and fits well with other aspects the Agency's
monitoring strategy and infrastructure. It has not previously been used
for a NAAQS, however, and this first application raises issues of
calibration (see below), standardization (see below), and sample
uniformity (noted above) that wet-chemical methods do not present. I
think Dirk Felton's suggestion to establish XRF as an FEM with ICP-MS as
the FRM is worth considering, with the caveat that methods requiring
extraction and digestion raise their own accuracy issues.

[Adequacy of XRF bias, precision, and detection limit]{.underline}

The adequacy of XRF measurement capabilities depends on the MQOs
(measurement quality objectives) established for the analytical method,
which in turn depend on the DQOs (data quality objectives) established
for compliance monitoring. In today's discussion it was noted that DQOs
required to protect public health will themselves depend on the level
and form eventually chosen for the NAAQS. With all these considerations
yet to be finalized, there are nevertheless certain points that are
already clear.

**Detection:** The NAAQS level proposed in the Federal Register is in
the range 0.1-0.3 ug/m^3^. The existing CSN and IMPROVE networks
demonstrate reliable (95% probability) XRF detection of non-spurious Pb
at filter loadings of 5-7 ng/cm^2^ (Attachment 2). For the low-volume
PM~10c~ FRM sampler, this corresponds to a real detection limit of about
0.003 ug/m^3^, more than an order of magnitude below the lowest
contemplated NAAQS level.

**Precision:** The declared goal for collocated precision is a 15% CV at
90% confidence. Quality assurance for IMPROVE includes regular XRF
reanalyses of a fixed collection of about 70 representative ambient
samples. Over 20 reanalyses have been performed of each sample at
approximately monthly intervals, yielding some 70 well-determined
analytical CVs. The typical (median) CV obtained for Pb has been 13%
(Trzepla-Nabaglo and White, 2008;
<http://secure.awma.org/presentations/AerosolAtmosphericOptics08/papers/81-Trzepla-Nabaglo.pdf>).
These results do not reflect flow and other sampling uncertainties but
do include observations at all concentrations, with a (relatively low)
mean loading of about 12 ng/cm^2^. As Dirk Felton observed, precision
for collocated samples will be sensitive to the minimum concentration
included in the calculations.

**Bias:** The declared goal is a system bias within 10% at 95%
confidence. Demonstrating attainment of these tolerances with XRF is
likely to be a challenge. The need to verify that the sample deposit is
uniform has already been noted. The other main difficulty will be the
absence of a suitable NIST-traceable standard for calibration. NIST
(2002) offers "air particulate on filter media" as SRM 2783, with a
certified Pb loading of about 32 ng/cm^2^, but gives a 95%-confidence
uncertainty of about 17% for this value. I am not aware of any
peer-reviewed examination of the claimed accuracies of commercially
available calibration foils, or even consistency among different foils.

[Specific analysis details in the FRM]{.underline}

Some aspects of XRF analysis require more prescriptive detail than the
draft FRM gives them. The most important are two that relate to method
accuracy.

**Audit filters:** Bias is to be assessed "through an audit using spiked
filters." The preparation of spiked standards for XRF analysis is
significantly more complicated than simply depositing a known quantity
of standard solution on a glass-fiber hi-vol filter and letting it dry,
as is now done. Deposit uniformity is needed for quantitative XRF, as
noted above. Achieving this uniformity in a liquid deposit on a Teflon
membrane is likely to require attention to surface phenomena. The most
relevant spiked filter would be created by actually sampling a pure
Pb-containing aerosol and determining the Pb loading from the weight
gain. XRF results for such a filter could be compared directly with
those for ambient samples, but the production of such filters would
require development and validation.

**Protocols:** The principals of EDXRF are universal but there is no
standard protocol for implementing them, as the Agency discovered two
years ago in its effort to "harmonize" XRF reporting from different labs
used by their PM~2.5~ speciation networks (Gutknecht et al., 2006;
<http://www.epa.gov/ttn/amtic/files/ambient/pm25/spec/xrfdet.pdf>).
Different instrument systems use different x-ray spectra generated by
different configurations of source anode, secondary target, and spectral
filter, different geometries of irradiation and detection, and different
spectral decomposition software based on different interpretive
strategies. Much of the spectral processing in commercial instrument
systems is proprietary and invisible to the user, making it difficult to
confirm which lines are used and how they are de-convoluted. Will the
Agency undertake to certify certain commercial systems for use?

For whatever analytical method is used, field blanks should be routinely
exposed and analyzed to detect possible contamination in the field and
laboratory. CSN and IMPROVE both report loadings below 3.5 ng/cm^2^ in
95% of their routine field blanks (Attachment 2), significantly
exceeding the FRM's proposed filter acceptance criteria (requiring 90%
to be less than 4.8 ng/cm^2^).

[Method interferences]{.underline}

I know of no additional method interferences.

**Attachment 1**: material excerpted and annotated from Nuclear
Instruments and Methods in Physics Research B 160 (2000) 126-138

Elemental composition and sources of air pollution in the city of
Chandigarh, India, using EDXRF and PIXE techniques

H.K. Bandhu, Sanjiv Puri, M.L. Garg, B. Singh, J.S. Shahi, D. Mehta, E.
Swietlicki, D.K. Dhawan, P.C. Mangal, Nirmal Singh

![](media/image8.wmf){width="6.409842519685039in"
height="5.157086614173228in"}

Samples were collected on 47 mm diameter, 0.8 lm pore size, cellulose
nitrate filter papers (Microdevices, Ambala, India). Filter paper was
mounted in an aerosol filter holder (Millipore, Cat No. xx50 04700)
having an inlet dispersion chamber to produce optimum particle
distribution on the surface of the filter. The air through the filter
paper was sucked at a flow rate of 12 l min^-1^ with the help of
diaphragmatic vacuum pump (Millipore, Cat. No. xx55 22050) and critical
orifice (Millipore, Cat. No. xx50 000 00). The flow rate was monitored
periodically for each sample with a rotameter and no cases of reduction
of flow rate due to filter clogging were experienced during the
sampling. The collection surface was directed downward to prevent
particle collection by sedimentation and the filter holder was protected
with a rain cover. All the sampling sites chosen for sampling were
located on the flat roof of building tops 40-60 feet high.

**Attachment 2:** material excerpted and annotated from Environ. Sci.
Technol. 2008, 42, 5235--5240

An empirical approach to estimating detection limits using collocated
data

Nicole P. Hyslop and Warren H. White

![](media/image9.wmf){width="7.109055118110236in"
height="1.101968503937008in"}![](media/image9.wmf){width="7.109055118110236in"
height="0.41653543307086616in"}

![](media/image10.wmf){width="4.958333333333333in"
height="1.2291666666666667in"} From field blanks From collocated
sampling

**Dr. Yousheng Zeng**

***Charge Question 1: What are your comments on the use of the
low-volume PM~10c~ FRM sampler as the Pb-PM~10~ FRM sampler?***

I support the EPA proposal to use the low-volume PM~10c~ FRM sampler as
the Pb-PM~10~ FRM sampler. The PM~10c~ FRM sampler is better defined and
better understood than the earlier PM~10~ sampler. This method will also
provide consistency with PM~10~ and PM~2.5~ monitoring network; data
comparability for evaluation of Pb-PM~10~ and PM~10~ inhalation pathway;
and monitoring operation efficiency (same samplers for both PM~10~ and
Pb-PM~10~).

However, I share the same concern with some committee members. With this
method, the monitoring results will be naturally lower because PM~10~
samples, not TSP samples, will be collected for Pb analysis. If the
revised Pb NAAQS is not set low enough to account for the absence of Pb
associated with particles larger than 10 μ, the new Pb NAAQS may not
provide additional protection to human health.

***Charge Question 2: What are your comments on the use of XRF as the
Pb-PM~10~ FRM analysis method?***

I support the approach proposed by Mr. Dirk Felton to use ICPMS (or AA
as he mentioned during previous consultation meeting) as FRM for sample
analysis and use XRF as FEM. A similar approach has worked well for
SO~2~ where a manual method is the reference method and instrumental
methods are FEM and widely used in day-to-day monitoring operations.

***Charge Question 3: What are your comments on the specific analysis
details of the XRF analysis method contained in the proposed Pb-PM~10~
FRM analysis method description?***

I don't have comments on this issue.

***Charge Question 4: Do you think the precision, bias, and MDL of the
XRF method for the proposed Pb range will be adequate?***

At this point, we really don't know what will be the final Pb NAAQS. It
appears that the proposed analysis method (either XRF or ICPMS) should
be adequate to produce needed monitoring data. However, it is highly
recommended to use the Data Quality Objective (DQO) model that EAP used
for evaluation of PMc in 2004. During the public conference call on July
14^th^, 2008, EPA indicated that EPA was working on a DQO model for Pb.
It would be most desirable to use the DQO model to help finalize these
parameters (precision, bias, and MDL).

***Charge Question 5: Are there any method interferences that we have
not considered?***

I don't have comments on this issue.

**Dr. Barbara Zielinska**

**Charge questions regarding FRM for Lead in Pb-PM10:**

1.  What are your comments on the use of the low-volume PM10c FRM
    sampler as the Pb-PM10 FRM sampler?

> As stated in my comments from March 23, 2008, regarding previous
> consultation on this subject, I support the use of the low-volume
> PM10c FRM sampler as the Pb-PM10 FRM sampler. This sampler has been
> well-tested, has well-defined cut-points and slopes and is readily
> available.

2.  What are your comments on the use of XRF as the Pb-PM10 FRM analysis
    method?

> Although XRF method has many advantages (is nondestructive, sensitive,
> relatively simple and inexpensive), it presents some problems related
> to the uniformity of material on the filter collection surface. ICP-MS
> method is extremely sensitive for lead, has traceable standards and
> the uniformity of material is not an issue. I would recommend ICP-MS
> as an FRM for the analysis of lead and XRF as an FEM (or one of the
> FEMs).

3.  What are your comments on the specific analysis details of the XRF
    method contained in the proposed Pb-PM10 FRM analysis method
    description?

> The XRF analysis method is well described in this document. Specific
> analysis details were addressed during the advisory teleconference
> meeting and are reflected in the lead discussants memos.

4.  Do you think the XRF method precision, bias and MDL for the proposed
    Pb range will be adequate?

> The method MDL, precision and bias seem to be adequate. However, for
> very low ambient concentrations of Pb, it may be challenging to
> achieve the required precision.

5.  Are there any method interferences that we have not considered?

    I am not aware of any additional interference.

    **Enclosure C -- Agency's Background and Charge Memorandum to the**

**CASAC AAMM Subcommittee**

![](media/image1.wmf){width="1.0833333333333333in"
height="1.0291666666666666in"}

**UNITED STATES ENVIRONMENTAL PROTECTION AGENCY**

**RESEARCH TRIANGLE PARK, NC 27711**

June 15, 2008

**[MEMORANDUM]{.underline}**

**SUBJECT:** CASAC Peer Review and Consultation on Monitoring Issues for
Lead National Ambient Air Quality Standard (NAAQS)

**FROM:** Lewis Weinstock

Acting Group Leader

Ambient Air Monitoring Group

Office of Air Quality Planning and Standards (C304-06)

**TO:** Fred Butterfield

Designated Federal Officer

Clean Air Scientific Advisory Committee

EPA Science Advisory Board Staff Office (1400F)

Attached are materials for review by the Clean Air Scientific Advisory
Committee's (CASAC) Ambient Air Monitoring and Methods (AAMM)
Subcommittee. These materials will be the subjects of a peer review and
consultation by the AAMM Subcommittee, scheduled for a teleconference to
be held on July 14, 2008. I am requesting that you forward these
materials to the AAMM Subcommittee to prepare for the peer review and
consultation.

This project, entitled *Lead (Pb) National Ambient Air Quality Standards
(NAAQS) Review: Monitoring Issues*, has been requested by EPA's Office
of Air Quality Planning and Standards (OAQPS), within EPA's Office of
Air and Radiation, in anticipation of potential revisions to the Pb
NAAQS. The peer review will cover the proposed Federal Reference Method
(FRM) for the measurement of Pb in particulate mater less than 10
micrometers in diameter (Pb-PM~10~). The consultation will cover the
need and approach for development of a low-volume Pb in total suspended
particulate (Pb-TSP) method as an FRM or Federal Equivalent Method
(FEM). Charge questions associated with both the peer review and the
consultation are provided below.

The upcoming consultation will support the EPA by providing scientific
advice as the EPA Administrator considers potential revisions to the Pb
NAAQS; a notice of final rulemaking is to be signed by September 15,
2008. We are requesting an expedited schedule to assist EPA in meeting
the September 15, 2008 deadline for finalizing the Pb NAAQS review.

We appreciate the efforts of you and the Subcommittee to prepare for the
upcoming meeting and look forward to discussing this project in detail
on July 14, 2008. Questions regarding the enclosed materials should be
directed to Mr. Kevin Cavender, EPA-OAQPS (phone: 919-541-2364; e-mail:
<cavender.kevin@epa.gov>).

**Document Associated with Subcommittee's Peer Review:**

-   **Attachment 1** -- ***Draft Federal Reference Method (FRM) Lead in
    PM10 (Pb-PM10)***

> **[Background and Summary]{.underline}**: In order for monitoring data
> to be used in determination of attainment with the NAAQS, the data
> must be collected with a FRM or FEM. A number of options under
> consideration for the Pb NAAQS indicator would require the EPA to
> develop a FRM and FEM criteria for the measurement of Pb in PM~10~.
> The EPA has proposed language for a FRM for Pb-PM~10~ based on the
> existing FRM sampler for low volume PM~10c~ in Appendix O to Part 50
> of the Code of Federal Regulations (CFR) coupled with analysis by
> x-ray fluorescence (XRF). The attached document includes the proposed
> regulatory text for the FRM for Pb in PM~10~.

**[Charge Questions]{.underline}**:

> *What are your comments on the use of the low-volume PM~10c~ FRM
> sampler as the Pb-PM~10~ FRM sampler?*

*What are your comments on the use of XRF as the Pb-PM~10~ FRM analysis
method?*

> *What are your comments on the specific analysis details of the XRF
> analysis method contained in the proposed Pb-PM~10~ FRM analysis
> method description?*
>
> *Do you think the precision, bias and MDL of the XRF method for the
> proposed Pb range will be adequate?*

*Are there any method interferences that we have not considered?*

**Document Associated with Subcommittee's Consultation:**

-   **Attachment 2 -- *Options for the Development of a Low Volume Lead
    in Total Suspended Particulate (Pb-TSP) Sampler***

**[Background and Summary]{.underline}**: Problems with the current
high-volume Pb-TSP sampler have been highlighted as part of the on-going
Pb NAAQS review. As part of the NAAQS review, EPA proposed network
design requirements that could result in the need for a significant
expansion and/or reallocation of Pb monitors. Due to the concerns over
the existing high-volume Pb-TSP sampler, EPA requested comments on the
need for a FRM or FEM low-volume Pb-TSP sampler. The attached document
discusses options for the development of a low-volume Pb-TSP sampler for
use in the Pb network.

**[Charge Questions]{.underline}**:

> *Would a low-volume Pb-TSP sampler be an improvement over the existing
> high-volume Pb-TSP sampler? What advantages and disadvantages do you
> see associated with a low-volume Pb-TSP sampler?*
>
> *What inlet designs would be best suited for a low volume Pb-TSP
> sampler? What designs are not appropriate for a low-volume Pb-TSP
> sampler?*
>
> *What is your preferred approach for the development of a low-volume
> Pb-TSP sampler, and why?*
>
> *If the EPA were to develop a low-volume Pb-TSP FRM, how important is
> it that the sampling capture efficiency be characterized for varying
> particle sizes?*
>
> *If the EPA were to develop a low-volume Pb-TSP FRM, should the new
> FRM replace the existing high-volume Pb-TSP FRM, or should the EPA
> maintain the existing FRM?*

*Is it appropriate to accept alternative sampler and inlet designs as
FEM?*

> *Are the proposed FEM testing criteria for Pb methods adequate to
> ensure equivalence of alternative sampler and inlet designs? If not,
> what additional testing requirements should be considered?*

Attachments

cc: Fred Dimmick, OAQPS/NERL

Robert Vanderpool, ORD/NERL

Karen Martin, OAQPS/HEID

Deirdre Murphy, OAQPS/HEID

Kevin Cavender, OAQPS/AQAD

Tim Hanley, OAQPS/ AQAD

Joann Rice, OAQPS/ AQAD

Phil Lorang, OAQPS/ AQAD

James Hemby, OAQPS/ AQAD

[^1]: "Standard Operating Procedure for the Determination of Metals in
    Ambient Particulate Matter Analyzed by Inductively Coupled
    Plasma/Mass Spectrometry (ICP/MS)", prepared by ERG for EPA under
    Work Assignment 5-03, ERG No.: 0143.04.005, EPA Contract No.:
    68-D-00-264, September 2005.