Soft Xray Spectromicroscopy of Black Carbon Aerosols

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Soft X-ray Spectromicroscopy of Black Carbon
Aerosols

• Fresnel zone plate focuses monoenergetic X-rays
  to a first-order focal spot (25-50 nm) at the
  sample plane
• Aperture blocks non-focused light and higher
  orders from the sample
• Transmitted X-rays are measured by single photon
  counting

Mary K. Gilles, Chemical Sciences
Division Lawrence Berkeley National Laboratory
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Data acquisition modes

• Image obtain image at fixed energy
• 1000x1000 micron to 1x1 micron

Linescan trace line as a function of energy
Line
Energy

• Stacks Images as a function of energy
• spectrum at each pixel
• spectromicroscopy

Stack Figure A. Hitchcock
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Single Energy Images
Biomass Burn
Marine Boundary Layer
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Near-Edge X-ray Absorption Fine Structure (NEXAFS)
Excitation of inner-shell (core) electrons
(K,L,M) Electron promoted to unoccupied
states form a short lived excited state, or
ionized All elements have an absorption edge in
the soft X-ray range (100-1200 eV)
Increasing Enegy

• Ionization
• 1s ? ? transitions saturated (single) bonds
• 1s ? ? transitions lowest energy-double or
  triple bonds

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Atmospheric Particle NEXAFS
Carbon edge 285-320 eV
1s?? CC CO carbonate
1s?s C-H phenolic OH
Marine boundary layer
Biomass burn
Lynn Russell-Marine boundary Layer Peter
Buseck-African Biomass Burn
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Metal Oxidation States
STXM-11 Feb 27 2004 evening
40227029
5 microns
5 microns
40x40 micron image
Metal oxidation states Binding information
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Objectives Atmospheric Science Program

• Mapping of Black Carbon/soot in Single Particles
• Lynn Russell
• Optical density
• Compositional mapping
• Organic vs inorganic (CaCO3)
• Assess the variation in Black Carbon/soot NEXAFS
  spectra
• soot surrogate for laboratory studies?
• Spectromicroscopy of Laboratory Generated soots
• Hope Michelsen
• Hybridization changes upon irradiation?

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Collaborative Participation
Current Needs

• Samples of either extracted/ BC or carbon with
  organics removed

Future-Mexico City Campaign

• Distance between two sites permits studies on
  atmospheric aging processes and development of
  mixing states
• Examine samples for details in carbon spectra,
  then collaborate to have same particles looked at
  by TEM EELS to get additional elemental data
• Samples collected on either TEM grids or Silicon
  nitride windows

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Acknowledgements
Funding BER Atmospheric Sciences
Program Bryan Marten Teacher, Lowell High
School, San Francisco Romain Planques Student
Intern, Ecole Normale Superieure,Paris ALS
Beamlines Tolek Tyliszczak, A.D. Kilcoyne, Tohru
Araki, Sirine Fakra Collaborators/Samples Lynn
Russell, Hope Michelsen Marin Robinson, P.
Buseck, K. Prather, D. Smith
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Microspeciation Technique Comparison