Overview and Status of Lead NAAQS Review and Overview of Agency Technical Documents on Lead NAAQS Monitoring Issues

1
Overview and Status of Lead NAAQS Review and
Overview of Agency Technical Documents on Lead
NAAQS Monitoring Issues

• Kevin Cavender and Joann Rice
• Presented at Clean Air Scientific Advisory
  Committees Ambient Air Monitoring and Methods
  Subcommittee
• Public Teleconference
• July 14, 2008

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Outline

• Status of lead NAAQS review
• Proposed Federal Reference Method (FRM) for
  Pb-PM10
• Options for the development of a low-volume
  Pb-TSP sampler

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Status of Pb NAAQS Review

• Proposed rule signed May 1, 2008
• Comment period closes August 4, 2008
• Final rule due to be signed October 15, 2008

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Proposed Pb-PM10 FRM
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Background on current FRM for Pb-TSP

• Existing FRM based on high-volume TSP sampler
  with atomic absorption (AA) analysis.
• 21 existing FEM all based on high-volume TSP
  sampler with various analysis options
• CASAC and others have expressed concerns with TSP
  sampler
• Cut point is affected by wind speed and
  direction

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Draft Federal Reference Method (FRM) for Pb-PM10

• Sampling and analysis method considerations for
  the proposed FRM for Pb-PM10
• Sampling considerations
• Recently promulgated low-volume (16.7 L/min)
  PM10c sampler with 46.2-mm PTFE filters from
  PM10-2.5 FRM
• Advantages
• More demanding performance criteria of Appendix L
  (PM2.5 FRM) with sampling at local conditions
• Sequential sampling capability to meet increase
  sampling frequency if needed
• Affords network efficiencies and consistencies
  with other PM monitoring networks with low-volume
  samplers
• Consistent with QA requirements for PM2.5 and
  PM10-2.5

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Draft Federal Reference Method (FRM) for Pb-PM10

• Analysis Method Considerations
• X-Ray Fluorescence (XRF)
• Advantages
• No complicated sample preparation or extraction
  prior to analysis
• Non-destructive
• Relatively cost effective
• Relatively low method detection limits (MDLs)
• On the order of 0.001 µg/m3 for low-volume
  collection
• Also used in other PM speciation monitoring
  programs (e.g., CSN and IMPROVE)

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FRM Charge Questions

• What are your comments on the use of the
  low-volume PM10c FRM sampler as the Pb-PM10 FRM
  sampler ?
• What are your comments on the use of XRF as the
  Pb-PM10 FRM analysis method?
• What are your comments on the specific analysis
  details of the XRF method contained in the
  proposed Pb-PM10 FRM analysis method description?
  
• Do you think the XRF method precision, bias and
  MDL for the proposed Pb range will be adequate?
• Are there any method interferences that we have
  not considered?

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Options for the Development of a Low-volume
Pb-TSP Sampler
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Overview of a Potential Low-Volume Pb-TSP Sampler

• A low-volume Pb-TSP sampler would consist of two
  parts the inlet and the air sampler.
• The air sampler could be based on the low-volume
  air samplers used in the PM2.5 and PM10 networks.
  
• A particular inlet design (either existing or
  new) would need to be specified.

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Low-Volume Pb-TSP Inlet Considerations

• A number of vendors offer what they refer to as a
  low-volume TSP inlet
• In many cases, these low-volume TSP inlets are a
  low-volume inlet with the PM10 impactor removed.
  
• An inlet of this design has many potential
  benefits
• the PM10 FRM inlet is commercially available,
• PM10 FRM inlet designs are uniform,
• the PM10 FRM inlet design is already promulgated.
• None of the samplers which use this inlet have
  currently been approved as a TSP FRM or FEM.
• Although the overall effectiveness of the PM10
  FRMs inlet (including its internal PM10
  fractionator) has been well-characterized, the
  aspiration characteristics of the inlet itself
  have not been well-characterized
• The omni-directional inlet design would eliminate
  variability in sampling efficiency due to wind
  direction.
• For larger particles (gt PM10), the sampling
  efficiency would vary with particulate size due
  to windspeed-dependent aspiration characteristics
  and internal particle losses through the sampler.
  
• Limited information at low wind speeds is
  available in the literature (Lee Kenny et. al.,
  JEM 2005)

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Plot of High Volume Sampler Efficiency vs. Wind
Direction
Data from - Wedding, et. al., (1977)
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Plot of Sampler Efficiency vs. Wind Speed

1. High volume data from - McFarland, et.al, (1979)
2. Low volume (louvered inlet) data from Kenny,
   et. al., (2005)

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Overview of a Potential Low-Volume Pb-TSP Sampler

• Advantages of a low-volume Pb-TSP sampler over a
  conventional high-volume Pb-TSP sampler include
• No variability in sampling efficiency due to wind
  direction
• Improved flow control
• Improved precision and bias
• Sequential sampling capabilities
• Reduced footprint requirement
• Reduced noise
• Network efficiencies with other low-volume PM
  samplers (i.e., PM2.5 and PM10 networks)
• No metal interferences for other metals (e.g.,
  copper) from brushes on motors

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Potential Approaches for Development

• Two approaches could potentially be used to
  develop a low-volume Pb-TSP sampler
• Develop a new Pb-TSP FRM
• Test and approve a new Pb-TSP FEM

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FRM Approach

• One option for the development of a low-volume
  TSP sampler is to describe in detail and formally
  promulgate a new FRM for TSP sampling based on
  the modern low-volume sampler platform, and then
  designate.
• Many of the FRM specifications from the PM10 FRM
  could be referenced
• Geometric specifications for a TSP inlet design
  would need to be selected from designs currently
  available or newly developed
• Available commercial products that met the
  promulgated description could be designated as
  FRMs

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FRM Approach (continued)

• Ideally, the sampler capture efficiencies over a
  wide particulate size distribution would be
  understood prior to promulgation as an FRM.
• Due to difficulties in generating and
  transporting the large diameter particles
  required for wind tunnel evaluation of a TSP
  sampler, it may not be feasible to develop the
  data necessary to determine sampler capture
  efficiencies for ultra-coarse particulate matter.
  
• It would be especially difficult to develop the
  necessary data under the short timeline of the Pb
  NAAQS Review.
• Rather than waiting to develop the sampler
  capture efficiency data prior to promulgation of
  a low volume TSP FRM, the EPA could promulgate
  the new FRM without a full characterization of
  the sampler capture efficiency

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FRM Approach (continued)

• Advantages of this approach include
• Faster low-volume TSP sampler development and
  approval
• No need to match old high-volume TSP FRM
  performance
• No wind-tunnel or field test data needed
• Issues with this approach include
• Performance of new FRM could be worse than
  current FRM
• Difficulties in relating historic Pb-TSP data to
  new data

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FEM Approach

• The second option for development of a low volume
  Pb-TSP sampler is to allow alternative inlet and
  sampler designs to be accepted as FEM Pb methods.
  
• Currently, the Pb FEM requirements do not specify
  if different sampler and inlet designs can be
  designated as FEM 53.33(d) seems to indicate
  that alternative samplers could be approved as
  FEM
• The EPA has historically only approved Pb-TSP
  methods based on alternative analysis methods
• The EPA requested comments on the appropriateness
  of allowing alternative Pb-TSP sampler designs
  based on the Pb FEM requirements
• Under this approach, collocated field testing of
  the low volume Pb-TSP sampler versus the current
  Pb-TSP FRM would be conducted. If the two
  samplers readings matched within some acceptable
  level, the EPA would accept the low volume Pb-TSP
  sampler as part of a FEM Pb method.

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FEM Approach (continued)

• The current Pb FEM requirements (40 CFR 53.33)
  call for field testing
• One or more site
• 10 or more filter pairs per site (5 valid pairs)
• Samplers orientated to minimize wind-direction
  differences
• Each filter is analyzed three times
• Precision of replicate analyses required to be
  15 or less
• Comparability for each filter pair (FEM vs. FRM)
  must be 20 or less

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FEM Approach (continued)

• Advantages of this approach include
• Fast FEM development and approval
• No need to perform wind tunnel testing to
  characterize sampler capture efficiency
• Some assurance of consistency with historic
  Pb-TSP data
• Issues with this approach include
• Requires field testing by vendors or other
  sponsors (e.g., the EPA, monitoring agencies)
• Low-volume Pb-TSP samplers may not match
  high-volume Pb-TSP samplers well enough to pass
  FEM requirements, especially considering the
  variability of the high-volume FRM

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Low Volume Pb-TSP Charge Questions

• 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?

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References

• Kenny, G Beaumont, G Gudmundsson, A Thorpe, A
  Koch (2005) Aspiration and sampling efficiencies
  of the TSP and louvered particulate matter
  inlets. J. Environ. Monitoring 7481-487.
• McFarland, A.R. Ortiz, C.A. and Rodes, C.E.
  Characteristics of aerosol samplers used in
  ambient air monitoring. Presented at 86th
  National Meeting of American Institue of Chemical
  Engineers (1979).
• Wedding, J.B. McFarland, A.R. and Cermak, J.E.
  (1977). Large particle collection characteristics
  of ambient aerosol samplers. Environ. Sci.
  Technol., 11(4)387-390.