1. Atmospheric Black/Brown Carbons
Mary K. Gilles
Rebecca Hopkins
Alexei Tivanski
Bryan Marten
Zi Wang
Lawrence Berkeley National Laboratory, Chemical Sciences Division, Berkeley, CA, USA.
*Lowell High School, 1101 Eucalyptus Drive, San Francisco, CA, USA.
Engineering, UC Berkeley

2. Interests What is the range of “soot” in the atmosphere
Can we distinguish between biomass burn & fossil fuel combustion
Can spectra be correlated with optical properties
Influence of burn type, fuel
Influence of aging and atmospheric processing

3. Black Carbon what to use in the lab for experiments?
GRAPHITE
- Highly ordered with strong sp2 bonds.
We have studied soot from resistively heated and micronized graphite.
Highly oriented pyrolytic graphite (HOPG) is essentially 100% sp2.
CARBON BLACKS
- Amorphous structure with a mixture of sp2 and sp3 bonds.
- Little or no presence of oxygen, nitrogen or hydrogen.
We have studied amorphous carbon and Palas soot.
COMBUSTION SOOT
- Lower carbon content than carbon blacks.
- A variety of oxygen containing functional groups are present.
We have studied soot produced in n-hexane, ethylene and methane flames, in addition to diesel soot.
What would you use in the lab to do an experiment
What is the range in possible things to use versus what the range is in the atmosphere
What is the range of black /brown carbon (soot )in the atmosphere?

4. Experimental Approach – STXM/NEXAFS
Scanning transmission X-ray microscopy (STXM) at the ALS
Experiments conducted at beamlines and at the Advanced Light Source.
Energy range of both beamlines covers the carbon and oxygen absorption edges.
K absorbs in carbon spectrum
Sample is distributed on Si3N4 substrate or coated TEM grid.
NEXAFS - element specific, sensitive to local bonding structure.
T. Tyliszczak, A.L.D. Kilcoyne designed & built

5. Data Acquisition Modes
Image at a single energy
Raster scan sample at a fixed energy
Stack
Records a sequence of images at multiple, closely spaced energies.
Allows a spectrum to be extracted from each image pixel.
Transmission spectrum
Vary X-ray energy and scan over a line.
less radiation exposure
than e-beam

6. Extracting Information C/O ratio
C=C
1s- s*
1s- p*
C-O, C=O
C=O
This spectrum on the left is a real black carbon
High pi* peak, second hump,
Tough to assign transitions in region , phenolic pi* obvious if present, but

7. Fitting and Assigning NEXAFS Spectra
Similar functional groups, different proportions BC
Reference Material
Carbonyls
Biomass Burn Aerosol
Carbonyls
Calculate the % that each functional group
contributes to total carbon
Compare sp2 to standard-HOPG 100%
Highly Oriented Pyrolytic Graphite

8. Quantifying the differences between “soots”
Flame soot
Biomass “soot”
more oxygen
higher sp2, more ordered
Submitted to J. Aerosol. Science

9. AGED BIOMASS BURN TAR BALLS Size Dependent Chemical composition
Tar balls: soot or HULIS?
tar ball: 55% C, 45% O;
BC: C>85%;
HULIS: ~55% C, ~35% O, ~10% H,N,S;
same shell thickness for all sizes
Δ << d
uniform shell density
Oxygenated Shell
Δ=42 ± 5 nm (sh=)
Tar balls-spectra & chemical composition more similar to HULIS than soot
Tar ball samples A. Laskin, J. Hand
Submitted to J. Phys. Chem. A

10. WHY? HOW? Flame What is the range of “soot” in the atmosphere
Can we distinguish between biomass burn & fossil fuel combustion
Can the spectral properties be correlated to optical properties
Influence of burn type, fuel
Influence of aging and atmospheric processing
A. Laskin, Desyaterik, collaboration & sample collection (EMSL, PNNL)
Samples collected w/ Moudi impactor-stage 7
Came in through back door-need to acknowledge people who actually organized the project
B. Malm, W. Hao (FSL), S. Kreidenweis, J. Collet
CSU & NPS,USFS
- sorry if list is incomplete)

11. Several types of images
Category 1,
Mostly C and O, generally have some type of inclusion in them, may look like a soot inclusion or look like an inorganic inclusion
Puddles of oil surround these
Category 2,
Mostly inorganic salts with some C and O, no oily puddles
Category 3
Look like soot, but may have some inorganic inclusions
SEM/EDX measurements, sample collection, motivation
Y. Desyaterik and A. Laskin
William R. Wiley Environmental Molecular Sciences Laboratory,
Pacific Northwest National Laboratory,

12. Carbon & Oxygen spectra Determine C/O
Determine% sp2
Correlate w/ other properties?
Row 1 pine needles, pine duff, alaskan core duff
Row 2, rice straw
Row 3 Chamise, juniper foliage stick, manzanita-problem w scan but first part looks like soot
~ 3x3 microns

13. FLAME Biomass burn
K doublet
C=C p*
C=O p*
C=C s*

14. Calculate the % sp2 from SpectraBC
Reference Material
Carbonyls
Compare % sp2 to standard-HOPG 100%
Highly Oriented Pyrolytic Graphite

15. Soot like cores in oily puddle Oily puddles w/ solid core
Category 1
C/O
%sp2
Ponderosa Pine Needles
70/30 32
Ponderosa Pine Duff
87/13 40
Alaskan Tundra Core Duff
82/18 25
Southern Pine Needles
69/31 44
Ceanothus (I)
78/22 31
Mean 77/23
Mean 34
Category 2
Rice Straw (I) 49
Puerto Rico Fern (dry) (I)
74/26 56
Puerto Rico Mixed Woods
80/20 60
Palmetto (I)
77/23 48
Mean 53
Category 3
Chamise (I) 81
Utah Juniper Foliage & Stick (I)
91/9 82
Utah Sage Rabbit Brush (I)
84/16 86
Mean 85/15
Mean 83
Soot Standard
Methane Soot 79
Mostly C & O
Soot like cores in oily puddle
Oily puddles w/ solid core
No oil puddles-external mixture?
Oil inorganic inclusion, no soot
KCl particles dominate, least soot/
Round C & O particle, some inclusions
Round particles, mostly C & O
KCl, NaCl dominate
Most sootish
Very sootish, no oil puddle
Similar to chamis, dominant soot , some K, no oil
Soot standard

16. Correlation between % sp2 & optical properties
532 nm 405 nm
Relationship  between single scattering albedo (ω) and % sp2 hybridization for the twelve wildland fuels and methane soot. Black and gray symbols represent ω recorded at 532 and 405 nm, respectively. ω for the twelve wildland fuels was measured using a dual wavelength photoacoustic instrument
The lessened ability of category 3 materials to absorb light may be attributed to the inorganic inclusions present in the biomass burn material, which could perturb extended p networks that give rise to long range order. These inorganic impurities are clearly not present in methane soot samples generated in the laboratory.
Optical measurements: K. Lewis and W. P. Arnott

17. Conclusions/Acknowledgements
STXM coupled with NEXAFS spectroscopy examine C/O ratios, % sp2 hybridization
Particulate matter ranges from high C/O w low % sp2 , high salt & lower C/O to “pure” soot
Potential for correlation of % sp2 hybridization w/optical properties
Burn type?
FLAME Organizers
Collaborators
A. Laskin, Y. Desyaterik-many many thanks
K. Lewis, P. Arnott-optical data
Jenny Hand-Tar Balls