What is Elemental
Carbon and How Do
Definitions Differ for
Different
Applications?
Bob Cary and David Smith
3/18/2003
Sunset Lab OCEC
1
Speciation of Carbon Aerosol
• Organic – Elemental – Inorganic
• Sources: OC – Many
EC – Pyrolysis of OC’s
3/18/2003
Sunset Lab OCEC
2
Analysis of Ambient Carbon Aerosols
• HOW
-???
• WHAT
-Elemental Carbon
-Organic Carbon
-Inorganic Carbonate Carbon
• WHY
-Health
-Visibility
-Source Tracer
-Climate Effects
3/18/2003
Sunset Lab OCEC
3
Carbonate and Organic Carbon
• Inorganic Carbonate Carbon
-e.g. CaCO3 (limestone dust – most
common)
• Organic Carbon
-Nearly all remaining carbon
-Primary-Secondary-Condensed Vapor
-Wide Range of Chemical and Physical
Characteristics
3/18/2003
Sunset Lab OCEC
4
EC Aerosol Species
(BC, Graphitic Carbon; NOT Soot)
• Elemental Carbon
-Extended Aromatic Rings of Carbon
Atoms
-Black (absorbs all visible light radiation)
(Degenerate Resonance Pi-bond electrons
in conductance bands; Metal-like)
-Refractory (does not melt or sublime,
even at high temperatures; >2000 C)
- Insoluble and Chemically inert at normal
temperatures
3/18/2003
Sunset Lab OCEC
5
Idealized EC
Structure
3/18/2003
Sunset Lab OCEC
6
STM of Graphitic Carbon
3/18/2003
Sunset Lab OCEC
7
STM of Graphitic Carbon
3/18/2003
Sunset Lab OCEC
8
Fractal Structure of EC
3/18/2003
Sunset Lab OCEC
9
Soot Representation
from Akhter, Chughtal and Smith, Applied Spectroscopy, 1985
3/18/2003
Sunset Lab OCEC
10
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
3/18/2003
Sunset Lab OCEC
11
Quantitative Measurement of EC
• DIRECT
• DIFFERENCE
3/18/2003
Sunset Lab OCEC
12
Direct Measure of EC
• Using Optical Properties and
Spectroscopic Techniques
i.e., Absorbance of Electromagnetic
Radiation
3/18/2003
Sunset Lab OCEC
13
Abs. Coeff. Vs. Size
e.g., from Horvath, Fuller, Taha
3/18/2003
Sunset Lab OCEC
14
Absorbance by EC
• Depends on wavelength
• Depends on size of particle
• Depends on morphology of particle (e.g.,
small monomeric clusters or fractals or
agglomerated fractals)
3/18/2003
Sunset Lab OCEC
15
Difference Measure of EC
by 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 atmosphere
Finally Do some Type of Direct Measurement
3/18/2003
Sunset Lab OCEC
16
T/O Analysis of Diesel
\------------- He ------------\----------- Ox ---------------\
1000
1000
900
T = 870 C 900
800
Int. Calib. Std.
800
700
700
600
500
600
Laser Transmission.
400
500
300
400
OC/EC Split Pt.
200
300
100
FID response to Carbon
0
200
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
Note: Very Little Pyrolysis
3/18/2003
Note: Small OC4 Peak
Sunset Lab OCEC
Note: EC Peak Location
17
T/O Analysis of Ambient
( wood smoke and metal oxides)
\-------------- He ----------------------\--------------- Ox ---------------------------\
35000
n.b., Sample Very Dark at Start
7200
30000
6200
25000
5200
20000
EC/OC Split Pt.
4200
15000
Absorbance
3200
10000
-------------------------------------------------------------------------------------------
2200
5000
1200
-------------------------------------------------------------------------------------------------200
0
1
17
33
49
65
81
97
Note: Location of EC Peaks
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
Note: Abs Increase at OC4
[Fe] = 7.8 ug/sq cm
3/18/2003
Sunset Lab OCEC
18
Sample with OC and
Carbonate Carbon
\------------------ He -----------------\--------------------- Ox ---------------------\
1000
Cal. Pk.
9200
900
8200
800
7200
700
6200
600
5200
500
CC
400
4200
300
3200
200
2200
100
1200
0
200
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
Note: Sharp OC4 Peak
3/18/2003
Sunset Lab OCEC
19
T/O of Pure Organic
EDTA
\------------------- He -------------\----------------- Ox -----------------\
30000
25000
20000
Cal. Pk.
15000
10000
5000
0
1
3/18/2003
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
Sunset Lab OCEC
20
Further Pre-Treatments
• Solvent Extractions (organic or water)
• Chemical Pre-Treatments
• Other Thermal-Treatments
3/18/2003
Sunset Lab OCEC
21
Pre-Treatment with Oxygen followed by
Full Thermal-Optical Analysis
Residual then Analyzed with TOA
\------- He -----------\---------- Ox --------------\
1000
2000
900
1800
870 C
800
1600
\-----------------He and Oxygen -------------\
Cal Pk.
700
1400
2000
600
530 C 500
600
1800
1200
1600
Cal. Pk
400
500
1000
1400
400
1200
800
300
300
1000
200
600
800
200
600
400
100
100
400
0
200
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
200
0
1
3/18/2003
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
Sunset Lab OCEC
22
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
3/18/2003
Sunset Lab OCEC
23
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?
3/18/2003
Sunset Lab OCEC
24