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Quanti tat ive Scann ing Electron Microsco py Method s to

Character ize A m bient A ir PM 2.5

D. V. Martello, R. R. An derson, C. M. White - NETLG. S. Casuc cio , S. F. Sch laegle, - R. J. Lee Group , Inc .

[email protected]

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Different Missions

EPA Protect the public health

DOE Assist the private sector in supplying

clean, abundant, and affordable energy

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PM 2.5 Regulatory Process

1997 National Ambient Air Quality Standards(NAAQS) for PM 2.5 based on health effects

Mean annual concentration < 15 g/m 3 Maximum concentration < 65g/ m 3

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Why Is DOE Concerned About PM 2.5 ?

Coal-based power systems contribute to PM 2.5 Primary particles:

Ultra-fine fly-ash (Spherical Alumino-silicates,SAS), carbon soot

Gaseous precursors: SO 2, SO 3, NO x React with NH 3 in the atmosphere to form ammonium sulfate and

ammonium nitrate particles

SIPs will likely restrict emissions from coal power plants.

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Ambient PM Monitoring and CharacterizationCurrent Project Portfol io

Upper Ohio River

Valley Project (UORVP)

Southeastern AerosolResearch andCharacterization Program(SEARCH)

Bravo Project

Great Smoky MountainsProject (GSMP)

Aerosol Research InhalationEpidemiology Study (ARIES)

Stuebenvil le Comp rehensive Air Monitoring Project (SCAMP)

DOE-NETL Prim ary Funding

DOE-NETL Cost-sharing

NETL-PGH In-hous e Monitorin g Stat ion

CMU/EPASupersite

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Regional Ambient PM Monitoring Sites

Coal-firedpower plants

1

2

UORVP Sites- Lawrenceville

- Holbrook

- Satellites

1

2

SCAMP Sites- Primary

- Satellites

1

1

- NETL In-house site

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Project Objective

Measure the degree that coal-fired utilitiescontribute to the primary fine-particulatematter load in ambient air.

Use Spherical Alumino-Silicates (SAS) as themeasure of coal-fired utilities contribution to theprimary fine-particulate matter load in ambient air.

Experimental Approach

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Experimental Objectives

Quantitatively validate the SEM methods.

Assess comparability of polycarbonate filters toFRM teflon filters.

Improve methods to account for most particlespecies on the filters.

Identify particle species including SAS, sulfates,and carbonaceous.

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Secondary Electron Image

SAS Particle

Carbon-rich Particle

Sulfur Droplet1 m

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Experimental Sample Collection

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Andersen RAAS 400 Speciation Sampler

Four flow channels

One at 16.7 L/m, teflon filter for FRM comparison

Two at 7 L/m, polycarbonate filters for SEM

One at 16.7 L/m, quartz filter for EC/OC

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Channel configurations

1: FRM teflon filter

2: Carbon denuder, Pd coated polycarbonatefilter, Nylasorb filter

3: Carbon denuder, uncoated polycarbonatefilter, Nylasorb filter

4: Carbon denuder, quartz filter, carbon filter

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Pre-weigh and post-weigh filters.

Sample SEM flow channels at 7 L/m found toproduce good particle dispersion at typical15 g/m 3 ambient air loading.

Sample ambient air for 24 hours.

Analyze SEM filters ASAP after sampling or store particle filters under controlledconditions.

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Comparison of Gravimetric Filter LoadingVariation:

RAAS Polycarbonate versus FRM andRAAS Teflon versus FRM

Filter TypeNumber of Filters

Avg. abs.difference,%

StandardDeviation

Polycarbonate 46 9.6 6.8

Teflon 163 5.6 6.8

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Scanning Electron Microscopy (SEM)

SEM analysis can provide both morphologyand composition information for use inindividual particle species determination.

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Scanning Electron Microscopy (SEM)

Image information

Secondary Electron (SE): Morphology

Backscattered Electron (BSE): Chemistry,Morphology

Composition information

X-ray (EDX/EDS): Chemistry

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Secondary Electron Image

SAS Particle


Sulfur Droplet1 m

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Backscattered Electron Image

SAS Particle


Sulfur Droplet1 m

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SEM Technique Validation

Test for uniform particle dispersion over thefilter surface.

Test for reasonable particle size distributionswithin measured fields.

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Experimental SEM Analysis

Mount filters with double-sided silver tape; no filter postsampling coating with carbon or metals

SEM conditions: 15kV; stable beam current; fixed WD

SE image fields at 1000x; center to perimeter of filter wedge analyzed; particle ID threshold monitored

Reference spectra used; 7 sec spectra acquisition

Pd coated filters for carbon particle identification C:Pd EDX ratio used for ID particle threshold

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Perim.Number

%

Center Number

%

Perim.Volume

%

Center Volume

%Particle TypeSAS 1.8 1.4 4.1 4.3C-rich 85.5 79.6 69.7 68.8Crustal 8.6 14.4 21.3 23.8S-rich 4.1 4.6 4.9 3.1

Comparison of Particle Species from filter Center and filter Perimeter, Excluding

Ammonium Sulfate Blobs

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23KX 0.2 m 33KX 0.2 m

Secondary Electron ImagesSAS

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Secondary Electron ImagesCarbon Chain Agglomerates

15KX 0.5 m 1 m7500X

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16KX 0.5 m 22KX 0.2 m

Secondary Electron ImagesCrustal

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Secondary Electron ImagesSulfur Deposits

15KX 0.5 m 0.2 m27KX

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Secondary Electron ImagesPlant Material

19KX 0.2 m 22KX 0.2 m

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Distributions - Spherical ParticlesAll Quads, Aspect < 1.5, - 2198 Particles

0

50

100

150

200

250

300

350

400

0 . 2

0

0 . 4

4

0 . 6

8

0 . 9

2

1 . 1

6

1 . 4

0

1 . 6

4

1 . 8

8

2 . 1

2

2 . 3

6

2 . 6

0

2 . 8

4

3 . 0

8

3 . 3

2

3 . 5

6

3 . 8

0

Average Diameter, um

# o

f P a r

t i c

l e s

All Quads, Aspect 0, 948 Particles

0

50

100

150

200

250

0 . 2

0

0 . 4

5

0 . 6

9

0 . 9

4

1 . 1

8

1 . 4

3

1 . 6

7

1 . 9

2

2 . 1

6

2 . 4

1

2 . 6

5

2 . 9

0

3 . 1

4

3 . 3

9

3 . 6

3

3 . 8

8


# o

f P a r t

i c l e s

All Quads, Aspect < 1.5, Si=0, S>0,1065 Particles

0

50

100

150

200

250

300

0 . 2

0

0 . 3

9

0 . 5

9

0 . 7

8

0 . 9

7

1 . 1

6

1 . 3

6

1 . 5

5

1 . 7

4

1 . 9

4

2 . 1

3

2 . 3

2

2 . 5

1

2 . 7

1

2 . 9

0

3 . 0

9

3 . 2

8


# o

f P a r t

i c l e s

All Quads, Aspect < 1.5, Si=0, S=0,185 Particles

0

510

1520

2530

35

40

45

50

0 . 2

0

0 . 3

0

0 . 4

0

0 . 5

0

0 . 6

0

0 . 7

0

0 . 8

0

0 . 9

0

1 . 0

0

1 . 1

0

1 . 2

0

1 . 3

0

1 . 4

0

1 . 5

0


# o

f P a r t

i c l e s

From Quantitative Scanning Electron Microscopy of Ambient Air 2.5m Particles Using, Air Quality II Conference, McLean, Virginia, September 19-21, 2000.

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Non-spherical ParticlesAll Quads, Aspect >= 1.5, Si>0,

2166 Particles

0

100

200

300

400

500

600

0 . 2

0

0 . 5

0

0 . 8

1

1 . 1

1

1 . 4

1

1 . 7

1

2 . 0

2

2 . 3

2

2 . 6

2

2 . 9

3

3 . 2

3

3 . 5

3

3 . 8

3

4 . 1

4

4 . 4

4

4 . 7

4


# o

f P a r t

i c l e s

All Quads, Aspect >= 1.5, Si=0, S>0,2533 Particles

0

100

200

300

400

500

600

700

0 . 2

0

0 . 5

6

0 . 9

1

1 . 2

7

1 . 6

2

1 . 9

8

2 . 3

3

2 . 6

9

3 . 0

4

3 . 4

0

3 . 7

5

4 . 1

1

4 . 4

6


# o f

P a r t

i c l e s

All Quads, Aspect >= 1.5, Si=0, S=0,382 Particles

0

50

100

150

200

250

300

0 . 2

0

0 . 3

9

0 . 5

9

0 . 7

8

0 . 9

7

1 . 1

6

1 . 3

6

1 . 5

5

1 . 7

4

1 . 9

4

2 . 1

3

2 . 3

2

2 . 5

1

2 . 7

1

2 . 9

0

3 . 0

9

3 . 2

8


# o f

P a r

t i c l e s

All Quads, Aspect >= 1.5, - 5081 Particles

0

100

200

300

400

500

600

700

800

900

1000

0 . 2

0

0 . 5

3

0 . 8

5

1 . 1

8

1 . 5

1

1 . 8

4

2 . 1

6

2 . 4

9

2 . 8

2

3 . 1

4

3 . 4

7

3 . 8

0

4 . 1

2

4 . 4

5

4 . 7

8


# o

f P a r t

i c l e s

From Quantitative Scanning Electron Microscopy of Ambient Air 2.5m Particles Using, Air Quality II Conference, McLean, Virginia, September 19-21, 2000.

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SampleStartDate

24Hour FRMug/m 3

SEM Ammonium

Sulfate

SEMCarbon

Particles

SEM AllCrustalParticleTypes

SEMSpherical Alumino-Silicates

SEMCrustal

SEMCa/SRich

SEM FeRich

Spheres

SEMMetalOxide

Particles

SEMMisc.

Particles

08/06/00 20.8 9.77 5.97 5.06 0.87 3.79 0.30 0.06 0.02 0.0308/08/00 23.4 13.95 4.93 4.51 0.24 3.67 0.51 0.00 0.01 0.0708/10/00 15.7 7.94 6.34 1.37 0.03 0.92 0.00 0.09 0.30 0.0308/12/00 7.6 2.08 3.57 1.95 0.09 1.10 0.07 0.09 0.39 0.2108/14/00 17.8 9.07 6.20 2.53 0.08 2.04 0.03 0.22 0.15 0.0108/16/00 9.5 4.76 2.72 2.02 0.26 0.60 0.67 0.00 0.37 0.1308/18/00 14.0 8.17 3.66 2.17 0.07 1.17 0.41 0.22 0.24 0.07

Analysis ResultsFRM and SEM particle class data

normalized to g/m 3

FRM and SEM particle class data normalized to g/m 3 (SEM particle class volume fraction x daily FRM). SEM datanormalized to IC ammonium sulfate analysis . From Quantitative Analysis of Ambient Air 2.5m Particles Using ScanningElectron Microscopy, 11 th International Conference on Coal Science, San Francisco, Oct. 2001.

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Carbon Values

0.000

1.000

2.000

3.000

4.000

5.000

6.000

7.000

8.000

0.00 0.50 1.00 1.50 2.00 2.50 3.00 3.50 4.00 4.50 5.00

R&P 5400 Total Carbon ug/m3

C C S E M C a r

b o n

u g

/ m 3

R&P Carbon versus SEM Carbon

From Quantitative Analysis of Ambient Air 2.5m Particles Using Scanning Electron Microscopy, 11 th International Conferenceon Coal Science, San Francisco, Oct. 2001.

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Conclusions

SEM sampling methodology is reasonablycomparable to the FRM, based on ug/m 3 filter loading.

The SEM technique provides satisfactoryresults to continue the method development.

Although the methodology may be subject toimprovement, it is of sufficient quality to applyit to the comparative measurement of SASparticles in a more comprehensive study.

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Future Work

Correlate the SEM results with bulk analysesof companion filters.

Analyze more filters to develop statistics on

distributional analysis of particle classes.

Use the palladium coating as an internalstandard for quantifying the particle species.

Revisit uncoated filters (check validity of calculating carbon by difference).

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Acknowledgements

Dr. Elias J. George NETL EnvironmentalSafety and Health Division

Traci Lersch R.J. Lee Group

The other PM 2.5 Sampling and Analysis team

members

Mr. Thomas J. Feeley Product Manager:Environmental and Water Resources, NETL

Documents

222_ACS_PM25_sem