What is Elemental Carbon and How Do Definitions Differ for...

3/18/2003 1Sunset Lab OCEC

What is ElementalCarbon and How DoDefinitions Differ for

DifferentApplications?

Bob Cary and David Smith

3/18/2003 Sunset Lab OCEC 2

Speciation of Carbon Aerosol

• Organic – Elemental – Inorganic• Sources : OC – Many

EC – Pyrolysis of OC’s


Analysis of Ambient Carbon Aerosols• HOW

-???• WHAT

-Elemental Carbon-Organic Carbon-Inorganic Carbonate Carbon

• WHY-Health-Visibility-Source Tracer-Climate Effects


Carbonate and Organic Carbon

• Inorganic Carbonate Carbon-e.g. CaCO3 (limestone dust – mostcommon)

• Organic Carbon-Nearly all remaining carbon-Primary-Secondary-Condensed Vapor-Wide Range of Chemical and PhysicalCharacteristics


EC Aerosol Species(BC, Graphitic Carbon; NOT Soot)

• Elemental Carbon-Extended Aromatic Rings of CarbonAtoms-Black (absorbs all visible light radiation)

(Degenerate Resonance Pi-bond electronsin conductance bands; Metal-like)-Refractory (does not melt or sublime,even at high temperatures; >2000 C)

- Insoluble and Chemically inert at normaltemperatures


Idealized ECStructure


STM of Graphitic Carbon


Fractal Structure of EC


Soot Representationfrom Akhter, Chughtal and Smith, Applied Spectroscopy, 1985


Formation of EC• EC created by Pyrolysis of OC• Thermal Energy breaks bonds creating

atoms and molecule fragments• Usually exist as Radicals• Subsequent collisions can cause

recombination to form new bonds• Extended C-C bonds build aromatics• Small atoms or fragments diffuse away

quickly; e.g., H2 or H-radicals


Quantitative Measurement of EC

• DIRECT• DIFFERENCE


Direct Measure of EC

• Using Optical Properties andSpectroscopic Techniquesi.e., Absorbance of ElectromagneticRadiation


Abs. Coeff. Vs. Size

e.g., from Horvath, Fuller, Taha


Absorbance by EC

• Depends on wavelength• Depends on size of particle• Depends on morphology of particle (e.g.,

small monomeric clusters or fractals oragglomerated fractals)


Difference Measure of ECby Removal of OC from TC

• Remove OC by Solvent of Chemical Means• Remove OC by Thermal Methods• Combinations of Above

e.g., heat in oxygen atmosphereFinally Do some Type of Direct Measurement


T/O Analysis of Diesel

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1 21 41 61 81 101 121 141 161 181 201 221 241 261 281 301 321 341 361 381 401 421 441 461 481 501 521 541 561 581 601 621 641 661 681 701 721 741 761 781 801

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\------------- He ------------\----------- Ox ---------------\

Note: Very Little Pyrolysis Note: EC Peak LocationNote: Small OC4 Peak

T = 870 C�

Laser Transmission.

FID response to Carbon

Int. Calib. Std.

OC/EC Split Pt.


T/O Analysis of Ambient( wood smoke and metal oxides)

[Fe] = 7.8 ug/sq cm

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1 17 33 49 65 81 97 113 129 145 161 177 193 209 225 241 257 273 289 305 321 337 353 369 385 401 417 433 449 465 481 497 513 529 545 561 577 593 609 625 641 657 673 689 705 721 737 753 769 785 801 817

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7200

Note: Abs Increase at OC4 Note: Location of EC Peaks

\-------------- He ----------------------\--------------- Ox ---------------------------\

-------------------------------------------------------------------------------------------

Absorbance

--------------------------------------------------------------------------------------------------

EC/OC Split Pt.

n.b., Sample Very Dark at Start


Sample with OC andCarbonate Carbon

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1 19 37 55 73 91 109 127 145 163 181 199 217 235 253 271 289 307 325 343 361 379 397 415 433 451 469 487 505 523 541 559 577 595 613 631 649 667 685 703 721 739 757 775 793 811

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Note: Sharp OC4 Peak

\------------------ He -----------------\--------------------- Ox ---------------------\

� CC

Cal. Pk.


T/O of Pure OrganicEDTA

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1 17 33 49 65 81 97 113 129 145 161 177 193 209 225 241 257 273 289 305 321 337 353 369 385 401 417 433 449 465 481 497 513 529 545 561 577 593 609 625 641 657 673 689 705 721 737 753 769 785 801 817

\------------------- He -------------\----------------- Ox -----------------\

Cal. Pk.


Further Pre-Treatments

• Solvent Extractions (organic or water)• Chemical Pre-Treatments• Other Thermal-Treatments


Pre-Treatment with Oxygen followed byFull Thermal-Optical Analysis

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1 11 21 31 41 51 61 71 81 91 101 111 121 131 141 151 161 171 181 191 201 211 221 231 241 251 261 271 281 291 301 311 321 331 341 351 361 371 381 391 401 411 421 431

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1 18 35 52 69 86 103 120 137 154 171 188 205 222 239 256 273 290 307 324 341 358 375 392 409 426 443 460 477 494 511 528 545 562 579 596 613 630 647 664 681 698 715 732 749 766

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\-----------------He and Oxygen -------------\

Cal. Pk

Cal Pk.

\------- He -----------\---------- Ox --------------\Residual then Analyzed with TOA

530 C�

870 C�


SUMMARY• There are Chemical and Physical Definitions of

EC• These Properties may differ for small particles

compared with bulk material• Analytical Methods should try to be consistent

with these definitions


Further Research on EC

• Can Additional Pre-treatments Help?• Do the Physical or Chemical Properties

Change?- From Source to final Collection or Measurement?

- During Analysis itself?

What is Elemental Carbon and How Do Definitions Differ for...

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