1

Carbon Functional Groups Identification and Source Apportionment of Fine Particulate Matter

withC(1s) NEXAFS Spectroscopy

Artur BraunDept. of Chemical & Materials Engineering

Consortium for Fossil Fuel SciencesUniversity of Kentucky, Lexington KY, USA

2

Acknowledgement• F.E. Huggins, N. Shah, G.P. Huffman, Univ. of Kentucky• K.E. Kelly, A. Sarofim, Univ. of Utah• B.S. Mun, Berkeley Nat’l Lab, Advanced Light Source• S. Wirick, C. Jacobsen, SUNY SB & Brookhaven Nat’l Lab, NSLS• M. Maricq, Ford Motor Company• W. Linak, US EPA Nat’l Risk Management Research Center• W. Harrison, USAF Wright Patterson AFB• J. Mcdonald, Lovelace Respiratory Research Institute• S. di Stasio, Istituto Motori, Napoli, Italy• A. Kubatova, EERC Univ. of North Dakota• M. Heuberger-Vernooij, EMPA

NSF Grant # CHE-0089133. NEXAFS was performed at Beamline 9.3.2 at theALS and Beamline X1A at the NSLS.

3

Direct correlation: Particle concentration ~ Mortality ratio

Suspected role in global climate forcing

Airborne fine particulate matter - Feinstaub

970

975

980

985

990

995

1000

0

10

20

30

40

50

1 2 3 4 5 6

Surv

ivor

s/10

00 p

erso

n ye

ars

Fine particles (μg/m3)

City

Portage, WI1Topeka, KS2Watertown, MS3Harriman, TN4St. Louis5Steubenville, OH6

Soot takes center stageW.L. Chameides, M. Bergin;Science (2002) 297 2214

“The 6 Cities Study”D.W. Dockery et.al., New Engl. J. of Medicine (1993):329/24 1753-1759.

4

NEXAFS

• Near-edge X-Ray Absorption Fine Structure Spectroscopy• For the analysis of soot molecular structure• Element specific – here we focus on the carbon

X-ray spectroscopy has been used for PM speciation before, but notfor carbon speciation !

Environm. Sci. & Technol. 41 (2007) 173.

5

C(1s) NEXAFS spectroscopy

- J. Stöhr, NEXAFS Spectroscopy, Springer, 1992, NY.- S.C.B. Myneni, Rev. Miner. Geochem. 49 (2002) 485.- A. Braun, J. Env. Monitoring., 2005, 7(11), 1059.

di Stasio, Braun. Energy & Fuels 2006, 20(1), 187 pp.

Element specific

• Sensitive to molecular structure

• Soot shows strong peak at 285 eVfrom C=C double bonds such as graphite or PAH

• Surface functional groups, SOM

• Goal: molecular fingerprint for sourceattribution

• Quantitative ?0

1

2

3

4

5

280 290 300 310 320 330

NEX

AFS

abs

orpt

ion

[a.u

.]

Energy [eV]

ethylene soot

carbon black

diesel soot

graphite

6

280 285 290 295 300

NEX

AFS

inte

nsity

[a.u

.]

Energy [eV]

SRM 1650Graphite SL-25

Environm. Sci. & Technol. 41 (2007) 173.

280 300 320 340 360 380 400

NEX

AFS

inte

nsity

[a.u

.]

Energy [eV]

7

NEXAFS of idle and load diesel soot

0.00

0.50

280 285 290 295

1.00

1.50

Energy [eV]

C-HC=O

C=C COOH

C-OHIdle

Load soot contains more graphitic material. Idle soot contains significantly more aliphatic material, incl. volatiles, residual oil, fuel, soluble organic matter,… .

phen

olic

arom

atic

alip

hatic

load

quin

oide

alky

late

d

Carbon 43/12 (2005), 2588

8282 284 286 288 290 292 294

Energy [eV]

C=C C=O

COOH

C-OH

C=Cgraphite-like

p-benzoquinoneNIST SRM 2975NIST SRM 1650

Utah, 2200 rpm

1800 rpm

1500 rpm

FTP 75

CNT

Utah, weathered

Exciton

Utah, generic

Comparison of various DPM samples

9

282 284 286 288 290 292 294Energy [eV]

LRRI

UND

DRY

MOIST

LEX

MIX

C=C

C-OH

COOH

C=O

C-H

NEX

AFS

abs

orpt

ion

[a.u

.]

Wood Smoke Studies

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

0 0.5 1 1.5 2 2.5 3 3.5

C-OHAromatic

Estimated Dry Time [yr]

LRRI MOISTLEX

MIXDRY

Rel

ativ

e Pe

ak H

eigh

t

Kreosote from dry wood and moist woodyields entirely different spectra

10282 284 286 288 290 292 294

Energy [eV]

LEX/LAW 103

LEX/LAW 86

LEX/Whalen

SRM NIST 1648

NEX

AFS

abs

orpt

ion

[a.u

.]

NEX

AFS

abs

orpt

ion

[a.u

.]

280 282 284 286 288 290 292 294

NIST 1648 Urban

LRRI Woodsmoke

FTP-75 day 3 DEP

90% DEP

50% DEP

10% DEP

Energy [eV]

Can We „Model“ Urban PM ?

c · Woodsmoke + (1-c) · DEP = Urban ?

11

0.72

0.76

0.8

0.84

0.88

0.92

0.96

0 10 20 30 40 50 60 70Weathering time [days]

PAHs Graphite

rela

tive

C=C

pea

kra

tio

DPM exposed to air, humidity, sun light for 2 monthsNEXAFS peak heights changeAromatic C=C peak decreases , then increasesPAHs decomposed ?

Diesel PM Weathering Study

282 284 286 288 290 292 294Energy [eV]

DEP

CNT

weathered

as received

12

Scanning Transmission X-ray Micro-spectroscopy

STXM is X-ray microscopy with chemical contrastResolution: ~ 100 nm, and chemical contrast of ~ 0.1 eVSoot core and extracts have different spectral characteristics

Spectrum = soot coreSpectrum = extract

Spectrum = graphiteand differential

Fuel (2004) 10 7/8, 997

13

Potential tool for in-situ reaction studies !(ozone + soot, etc…)

Photochemistry and De-carboxylation

0.6

0.7

0.8

0.9

1

1.1

1.2

282 284 286 288 290 292 294

Energy [eV]

C=C C=O

COOH

C-OH

Exposure time t = 120 msec

600 msec

600 msec

120 msec

0.5

1

1.5

100 200 300 400 500 600 700Exposure time [msec]

R2CO

3

Intense X-ray beam of the STXM microscope generates nascent oxy-gen from air.

Upon irradiation, COOH carboxyl peak intensity decreases, and new peak evolves - probably from an organo-carbonate.

Alginic acidAtm. Environment 40/30 (2006) 5837and Special Issue in J. Electron Spectr. & Related Phenomena on Radiation Damages; in press

14Energy [eV]

Diesel Soot

25 °C extract

282 284 286 288 290 292 294282 284 286 288 290 292 294

Energy [eV]

Urban PM

25 °C extract

282 284 286 288 290 292 294Energy [eV]

Wood Smoke

25 °C extract

C=C

C=C

C-O

H

C=O

C-O

H

C-O

H

C=O

C=O

CO

OH

CO

OH

CO

OH

C=C

NEX

AFS

abs

orpt

ion

[a.u

.]PM and extracts may have entirely different,if not controversal spectral characteristics

15

Diesel exhaust PM generated with oxidizer has higher genotoxicity

0.8

0.9

1.0

1.1

1.2

1.3

1.4

527 DEC 603 Ref

Incr

ease

in g

enot

oxic

ity

(pro

duct

ion

of b

-gal

acto

sida

se)

Incr

ease

in

geno

txic

ity

Total water extracts (25°-300°C)

280 285 290 295 300

527 DEC

603 Ref

Energy [eV]

A. Kubatova, A Braun, in preparationDe Marini et al., Bio-assay directed fractionation and mutagenicity of exhaust particles, Env. Health Persp. 2004, 112(8), 814-819

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Thank you

17

Carbon, 43(1), (2005) 117-124.

NEXAFS vs. EELS

EELS and NEXAFS have similar spectra. TEM microscopes often come with an EELS spectrometer. But EELS spectra from TEM look blurred, almost entirely useless for quantitative studies.280 285 290 295 300

Inte

nsity

[a.u

.]

Energy [eV]

NEXAFS BL 9.3.2 ALS(Total Electron Yield)

NEXAFS BL 9.3.2 ALS(Sample current)NEXAFS BL X1A NSLS(STXM)

EELS in connectionwith TEM

Diesel soot powder from oxygenateddiesel fuel under load engine

Note: this concerns not ISEELS such as the ones by Hitchcock & coworkers

18

0

0.5

1

1.5

280 285 290 295 300

ferrocenereference

Energy [eV]

C(1s) NEXAFS confirms WAXS results:catalytic suppression of soot formation by ferrocene

19

Suggested NEXAFS Peak Assignments for DPM Extract

Energy [eV]

NE

XA

FS in

tens

ity [a

.u.]

282 284 286 288 290 2920

1.05

2.1CO3

2-

COOH

C-OH

C=OC=C

C-H

20

C=C

CO

HC

OO

H

Energy [eV]280 284 300288 296292

Different PM samples show complex patterns in NEXAFS which cannot be easily attributed to the PM polarity

NE

XA

FS in

tens

ity [a

.u.]

21

NEXAFS of soot, oil, and fuel

0

0.5

1

1.5

280 285 290 295 300Photon energy [eV]

Soot

C=C

C-H

Oil

Mix A

Diesel

284 285 286

287 287.5 288

Spectra of soot, lubricant, fuel.

Allows for chemical speciation of samples, and determination of oxidation states.

Fuel (2004) 10 7/8 997-1000.

22

Catalytic suppression of soot formation in diesel engines

280 285 290 295 300

Diesel soot / ferrocene doped fuelGraphite SL 25Diesel soot / Ford motor vehicle

NEX

AFS

inte

nsity

[a.u

.]

Energy [eV]

FerroceneMetastable molecule = ironatom sandwiched between two cyclopentadienyl rings.

Dramatic decrease of C=C bond contribution in soot; increase in aliphatics

Mixing diesel fuel with ferrocene

23

Soot Extracts

280 285 290 295 300

Energy [eV]

25oC

50oC

100 oC

150 oC200 oC

250 oC

Soot powder

Diesel soot and extractsFord Motor Company

Separation of diesel soot into solid core and volatile fractions with sub-critical water facilitates subsequent decomposition of NEXAFS spectra.

0

0.5

1

1.5

2

280 285 290 295 300Energy [eV]

Extract

Residual

Soot as prepared

Extracts do contain material with C=C bonds

From reference diesel fuel

24

Soot ResidualsSeparation of diesel soot into solid core and volatile fractionswith sub-critical water facilitates subsequent decomposition of NEXAFS spectra.

280 285 290 295 300

25C 527250C 527300C 527

Energy [eV]

Soot Residuals

At low temperatures polar species like carboxylates and quinones are extracted.

282 284 286 288 290 2920

1.05

2.1

Energy [eV]

R2CO

3

COOH

C-OH

C=OC=C

C-H

benzo-quinone

Proposed peak assignment for extracts.

25

Correlation of Toxicological Results and Spectra ?

0.9

1

1.1

1.2

1.3

1.4

1.5

1.6

0 50 100 150 200 250 300 350

527/DEC603/Reference

Extraction Temperature [oC]

0.20.30.40.50.60.70.80.9

1

0 50 100 150 200 250 300 350

603 Ref527 DEC

Extract Temperature oC

Cell cultures exposed to a series of subcritical water extracts. Protein fold increase is a measure for toxic response.

A. Kubatova, A Braun, in preparation

26

Spectra of some solid carbon samples

280 285 290 295 300

Graphite SL 25Diesel soot / Ford motor vehicleFurnace deposits / Beech woodEthylene soot / Bunsen burnerNIST Urban PM

NEX

AFS

inte

nsity

[a.u

.]

Energy [eV]

Systematic and significant differences in the spectra depending on their origin

Soot spectra contain significant intensity from C=C bonds ~ 285 eV.Urban PM and wood creosote spectra contain significant intensity from aliphatics ~ 287 eV.

27

0.4

0.5

0.6

0.7

0.8

0.9

1

1.1

1.5

2

2.5

3

3.5

270 280 290 300 310 320

Urban_PM_summary

SC averaged NIST 1648 pellet

tey averaged NIST 1648 pellet

corrected energy

0.55

0.6

0.65

0.7

0.75

0.62

0.64

0.66

0.68

0.7

0.72

0.74

0.76

0.78

280 285 290 295 300

Urban_PM_summary

LAW 103 LAW 86

energy

-0.2

0

0.2

0.4

0.6

0.8

1

1.2

270 275 280 285 290 295 300 305

FTP-75 day 3LRRINIST 1648composition

Energy