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

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

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?

Experimental Approach – STXM/NEXAFS Scanning transmission X-ray microscopy (STXM) at the ALS Experiments conducted at beamlines 5.3.2 and 11.0.2 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

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. 104 - 105 less radiation exposure than e-beam

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 286-287, phenolic pi* obvious if present, but

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

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

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

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)

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,

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

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

Calculate the % sp2 from Spectra BC Reference Material Carbonyls Compare % sp2 to standard-HOPG 100% Highly Oriented Pyrolytic Graphite

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

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

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