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Characterization of Coarse PM Using Passive Samplers
R Willis1, G Norris1, T Watkins1
E Sawvel2, D Boysen2, N Kumar3, T Peters2
G Casuccio4
1US EPA, Office of Research and Development2Dept. of Occupational and Environmental Health, University of Iowa
3Dept. of Geography, University of Iowa4R.J. Lee Group, Inc.
2009 National Ambient Air Monitoring Conference
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UNC Passive Sampler
•
Consists of a standard SEM stub with a mesh cap
•
Small, unobtrusive (size and weight of a nickel)
• Easy to use
•
Inexpensive and reusable
• No power requiredWagner, J. and D. Leith. Aerosol Science and Technology. 2001, 34(2), 186-192.
Wagner, J. and D. Leith. Aerosol Science and Technology. 2001, 34(2), 193-201.
Wagner, J. and D. Leith. Journal of Aerosol Science. 2001, 32, 33-48.
Ott, D. and T. Peters. Aerosol Science and Technology. 2008, 42(4), 299-309.
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Large particles settle
SEM Stub
If wind speed is high,
particles affected by
turbulent inertia
Round Cap
with Hole in Center
Substrate
Screen
Small particles diffuse
glass (optical)
carbon tab or
polycarbonate (SEM)
grid (TEM)
How it Works
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Particle Loading on Passive Sampler Phoenix 7-day exposure, 100x magnification
Week 1 Week 2
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How it Measures
Calculated as function of particle size using theory checked in wind tunnel
Deposition Velocity
Ambient PM10-2.5
Concentration
Flux to Sampler=
Determined by Computer-
Controlled SEM or optical microscopy
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CCSEM with X-ray microanalysis provides size, composition, and morphology of individual particles
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Potential Applications
•
Evaluate spatial/temporal variability of PM10-2.5
mass and composition
Source apportionment
Nuisance dusts
•
Assess personal and workplace exposures for relating to adverse chronic health effects
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•
Phoenix (2005)•
Iowa City (2006, optical samplers)1
•
Birmingham (2005, 2006, 2008)•
St. Louis (2006, 2007)
•
Delhi, India (2007,2008)•
Cleveland (2008, 2009, 2010)
1Ott, D., N. Kumar and T. Peters. Atmospheric Environment. 2008, 42 746-756.
Field Evaluations
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Phoenix PM10-2.5 Results
0
10
20
30
40
50
60
Week 1 Week 2
PM10
-2.5 (u
g/m
3 )
FRM
UNC, Optical
RJLG
EPA
UNC, Photo SEM
CDHS
PM10-2.5 Accuracy and Precision Phoenix, 2005
UNC optical: optical microscopy, Univ. North CarolinaUNC photo SEM: SEM images + Image J, Univ. North CarolinaCDHS: CCSEM, California Dept. of Public HealthRJLG: CCSEM, RJ Lee Group, Inc.
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0
5
10
15
20
25
Trial 1 (10 d) Trial 2 (16 d) Trial 3 (12 d)
PM10
-2.5 (µ
g/m
3 )
FRM
Passive
PM10-2.5 Accuracy and Precision Birmingham, 2008
Passive sample precision = Std. Dev. of 2 co-located passive samples
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•
Objective: Assess the spatial variability of PM10-2.5
mass and composition in Cleveland using a network of passive samplers
Cleveland Scoping Study August 12 - September 2, 2008
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•
26 sampling sites selected to maximize the variability observed in preliminary surface PM10
concentrations•
Samplers deployed for 7-day intervals over 3 consecutive weeks
•
At each site, two passive samplers (one for optical and one for CCSEM analysis) co-
located within a protective shelter•
Results from CCSEM analysis are presented
Cleveland Field Sampling
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Cleveland sampling locations2008 Scoping Study
Sites selection maximizes the variability observed in preliminary surface PM10
estimates
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Weekly PM10-2.5 by Site
(samplers from site 3 went missing.)
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•
81.9 81.8 81.7 81.6
41.3
41.4
41.5
41.6
1
2
345
6
9
10
11
12
15
16
17
18
20
21
22
23
2627
30
32
34
35
36
4A
81.9 81.8 81.7 81.6
41.3
41.4
41.5
41.6
510152022253035
PM10-2.5 (μg/m3)
5 miles
Parma
East Cleveland
Brooklyn
Lake Erie
Lakewood
Brook Park
Valley View
Brooklyn Heights
Latit
ude
(deg
rees
)
Longitude (degrees)
ClevelandDowntown
81.9 81.8 81.7 81.6
41.3
41.4
41.5
41.6La
titud
e (d
egre
es)
Spatial variability of PM10-2.5
measured over 3-week study period
3-wk mean
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•
Distinct pattern with highest concentrations centered on the industrial valley
•
1-week average PM10-2.5
across sites
Low: 4 (±
3) µg/m3
High: 62 (±12) µg/m3
Spatial Variability: Mass
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Data Quality Results
•
Overall precision = 17% (field + analytical)•
CCSEM reproducibility = 4% (repeat analyses of 12 randomly-selected samples)
•
Blanks ~ 5 ±
3 µg/m3
(10 field blanks)•
Recovery = 96% (86 valid of 90 deployed samples)
•
FRM PM10-2.5
measurements were not available to determine passive sampling bias
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Data Quality Results •
Avg. passive sampling precision = 17% (field sampling variability plus CCSEM precision)
•
CCSEM analytical reproducibility = 4% based on repeat analyses of 12 randomly-selected samples
•
FRM PM10-2.5
measurements were not available to determine passive sampling bias
•
Avg. Blank ~ 5 ±
3 µg/m3
based on analysis of ten blanks
•
Only 4 of 90 samples collected were invalidated due to damage or loss
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•
X-ray microanalysis provides particle elemental composition
•
Particles classified into 9 particle types using chemistry-based rules
•
Number of particles analyzed ranged from 560 to 801
•
Preliminary results shown in comparison across 3 sites for week 3
Spatial Variability: Composition
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Inter-site Composition Variability PM10-2.5
mass fraction by particle type, Week 3
Site 4A12.0 µg/m3
Site 6 (GT Craig)30.2 µg/m3
Site 3012.5 µg/m3
Al-richCa/S-richCa-richC-richFe oxideFe-richmetal-richMisc.NaClNa-richpollenSi/Al-richSi-rich
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Random subset of low-
resolution CCSEM images from Site 6, week 3. Images show mix of dull gray (carbon-
rich and/or plant material) and brighter particles (minerals & metal-rich). Bright iron-
oxide spheres reflect steel processing activities.
Random subset of CCSEM images from Site 30, week 3. Carbon-
rich particles dominate.
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•
Central site monitoring of PM10-2.5 is unlikely to reflect true exposure given the observed spatial variability
•
Passive sampling can help identify local PM sources
•
An inexpensive network of passive samplers provides information typically unavailable with conventional PM10-2.5
instruments.
Implications
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•
Currently only 1 commercial lab (RJ Lee Group) provides CCSEM analysis of passive samplers
•
Concentrations are not available in real-time•
Long exposure periods (1 week or more) are typically required for ambient monitoring
•
Software tools to manage and interpret the large CCSEM data sets are still in development
•
PM2.5
underestimated; further evaluation of accuracy/precision required
Limitations
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Future Plans
•
Analyze composition variability across all Scoping Study sites
•
Process samples from Cleveland Summer ′09 Intensive
•
Winter ′10 Cleveland Intensive
•
Extend method to PM2.5
and ultrafines?
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•
Robert Vanderpool, EPA RTP
•
Robert Murdoch, RTI International
•
Michael Wheeler, Alion
Science and Technology
•
Mark Conti, EPA Region 5
•
George Young, Marvin Rogers, and Frank Saridakis, Cleveland Division of Air Quality
•
Jay Turner, Washington, University
•
Traci Lersch, and Roger West, RJ Lee Group, Inc.
•
Jeff Wagner, California Department of Public Health
•
Jerray
Battle, North Carolina Central University
Acknowledgements
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Although this work was reviewed by EPA and approved for presentation, it may not
necessarily reflect official Agency policy.