Preliminary results from spectral characterization of aerosol absorption during FLAME

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Preliminary results from spectral
characterization of aerosol absorption during
FLAME
Colorado State University
University of Nevada/DRI

• Gavin McMeeking
• Sonia Kreidenweis
• Jeffrey Collett, Jr.
• Lynn Rinehart
• Guenter Engling
• Rich Cullin
• Kip Carrico

Pat Arnott Kristin Lewis
Lawrence Berkeley NL
US Forest Service
Melissa Lunden Thomas Kirchstetter
Cyle Wold Patrick Freeborn
October 30, 2006 Group meeting
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Biomass burning climate effects
Focus of this work
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Biomass burning visibility effects
Focus of this work
adapted from Malm et al. (2004)
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Classifying carbon
Terms describing carbonaceous aerosol are defined
from how each is measured and used
Chemical structure controls light absorption
(electrons are highly mobile in EC/BC)
Light Absorbing Carbon
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Evidence of visible light absorption by organic
carbon
Andreae and Gelencser, 2006 (AG06)
Brown carbon Light-absorbing organic matter in
atmospheric aerosols of variousorigins soil
humics, HULIS, tarry materials from combustion,
bioaerosols
Patterson and McMahon, 1984 and Bond, 2001
Observed smoldering material and residential coal
combustion can contain large amounts of Cbrown
Kirchstetter et al, 2004
Demonstrated an OC contribution to spectral light
absorption for several biomass from SAFARI
same technique used in this study
Hoffer et al., 2005, Havers et al., 1998,
Gelencser et al. 2000 and others
Fine continental aerosol contains organic carbon
with properties similar to naturalhumic/fulvic
substances.
Andreae and Crutzen, 1997
Biogenic materials and their oxidation and
polymerization products can absorb light
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Impacts of Cbrown (AG06)
Light absorption measurements
The presence of Cbrown will lead to uncertainty
in the conversion of measured attenuation to a
BC concentration if the conversion factor differs
from that assumedfor soot.
Tropospheric photochemistry
Care must be taken when extrapolating absorption
measurements at mid-visible wavelengths over the
solar spectrum. Downward UV irradiance can be
underestimated if the light absorbing carbon has
a stronger wavelength dependency than that
typically assumed for soot.
Cloud chemistry and cloud light absorption
If a significant fraction of Cbrown is soluble in
water it can alter cloud droplet light
absorption, particularly in the UV. Could be an
important process in clouds formed on/near smoke
plumes.
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Impacts of Cbrown (AG06)
Thermochemical analysis
Significant contributions of Cbrown to
tropospheric fine aerosol could bias
traditionalmeasurement techniques that are
carried on to calculations of light
absorption. Cbrown is volatilized over a wide
range of temperatures and may be classified
partly asOC and partly as EC (Mayol-Bracero et
al., 2002). Biomass smoke contains inorganic
components that catalyze oxidation of soot
andCbrown, resulting in lower evolution
temperatures (Novakov and Corrigan, 1995). Not
known if Cbrown is prone to charring and if so,
to what extent the TOT and TOR OC/EC correction
methods are applicable. Larger differences
between measurement techniques are seen for
non-urban and biomass burning samples than for
urban andlaboratory-generated soot samples (Chow
et al., 2001).
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Experimental setup for FLAME
May/June 2006
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Filter samplers for chamber burns
IMPROVE
Hi Vol
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Biomass types burned during FLAME (chamber)
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Lawrence Berkeley Lab visit
September/October 2006
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Visible light attenuation measurements
Spectrometer(Ocean Optics S2000)
Light box
Ten LED light source
400 1100 nm range with sub nanometer resolution
Kirchstetter et al., 2004
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Attenuation calculation
Sample intensity
Reference filter intensities
Attenuation
Transmission
Sample filter intensity
Attenuation spectral dependence (Bohren and
Huffman, small particles)
constant
attenuation exponent assumed 1 for EC
wavelength
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Untreated ATN measurements
Base case measurement of filter attenuation as a
function of wavelength
Measured for all burns A-S on at least one 1.14
cm2 punch from B HiVol quartz filter sample
(PM2.5)
Ceanothus HiVol sample
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Normalized light ATN for selected burns
Absorption exponent ranged from 0.8 (chamise,
lignin) to 3.5 (Alaskan duff, rice straw)
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ATN base case results
Kirchstetter et al., 2004
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Filter solvent treatments
Selected filter samples were extracted with
hexane, acetone and water to determine role of
organic carbon and water soluble carbon on filter
attenuation
Each organic solvent extraction was performed for
one hour and water extraction for 12 hours
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Filter solvent treatments
Puerto Rican mixed woods
No treatment
Acetone extraction
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Filter treatments Lodgepole Pine
water extraction results in no change
(normalized)
1.5
1.0
0.9
acetone extraction reduces attenuation coefficient
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Filter treatments Alaskan duff
hexane extraction results in increase (normalized
only)
3.5
water extraction results in largest reduction
3.1
2.3
1.0
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Filter treatments Alaskan duff
very weak attenuation by back half of filter
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Total carbon measurementsEvolved Gas Analysis
(EGA)
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Total carbon measurementsEvolved Gas Analysis
(EGA)
to CO2 analyzer
light source
fiber optic to spectrometer
fan
sample oven
catalyst oven
light collector
O2 carrier gas
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EGA light source upgrade
solid quartz tube
filter holder
brighter light source
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Example EGA (no treatment)
Burn B, chamise
- flaming combustion - Low OC/EC ratio
EC
attenuation at 544 nm
OC
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Example EGA (no treatment)
Burn P, southern pine
- mixed combustion
OC
EC
slight increasedue to oven heat
pyrolized carbon ATN
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Example EGA (no treatment)
Burn G, Alaskan duff

• Smoldering combustion
• High OC/EC ratio

OC
no EC?
pyrolized carbon ATN
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Attenuation coefficients
Attenuation divided by total carbon mass
How will results change when ATN divided by
EGA-determined OC and EC?
Kirchstetter et al., 2004
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Effect of solvent treatments on EGA
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Front/back half filter EGA results
Burn L, lodgepole pine
whole filter (26 ug cm-2)
- mixed combustion
front half (20.5 ug cm-2)
back half (5.1 ug cm-2)
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EGA spectrometer measurements
Burn M, PR fern
- mixed combustion
oven signal
No attenuation
Large change in ATN(EC evolving here)
charring
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EGA spectrometer measurements
Burn G, Alaskan duff
- smoldering combustion - very little EC
oven signal
No attenuation
No large ATN changeas seen in PR fern
charring
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Summary of work done so far
Attenuation

• Strong relationship between combustion phase and
  attenuation/absorption exponent
• Exponent decreases following acetone treatment
  and in one case water treatment
• Attenuation coefficients (by TC) higher for
  flaming fuels versus smoldering fuels
• Smoldering biomass fuel emissions that contain
  very little-to-no EC still attenuate light at low
  wavelengths.

Evolved gas analysis

• Measurements across entire visible range may
  provide additional insight on OC/EC charring
  issues and light attenuation as a function of
  carbon evolution temperature
• Smoldering fuels charred significantly during
  EGA analysis
• All treatments led to a reduction in TC, most
  likely due to mechanical separation of particles
  from the filter matrix
• Water treatment not only reduced amount of EC
  and increased the EC evolution temperature, most
  likely due to the removal of inorganic ions
  acting as catalysts

Kirchstetter et al., 2004
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Work to be done
Attenuation

• Quantify ATN and ATN coefficient changes under
  different treatments for TC and OC/EC
• Compare filter-based ATN measurements to
  photoacoustic absorption measurements,
  nephelometer scattering measurements and
  extinction cell data
• Compare ATN measurement results to chemical
  composition data from a variety of sources
• Explore the significance of ATN results to
  visibility, radiative forcing and UV
  photochemistry for areas influenced by biomass
  burning emissions
• Additional measurements of ATN for different
  polarity solvent treatments
• Compare smoldering and flaming phases of
  combustion for the same fuel (FLAME2)
• Analyze IMPROVE backup filters for gas-phase
  adsorption effects on ATN
• Compare FLAME results to other studies (fresh
  vs. aged smoke?)
• Develop method to deconvolute attenuation into
  brown carbon and black carbon components

Evolved gas analysis

• Compare EGA results for OC/EC determination to
  Sunset analyzer
• Analyze spectrometer measurements taken during
  EGA runs and try to determine optical properties
  of pyrolized carbon

Kirchstetter et al., 2004
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Acknowledgements
Joint Fire Science Program National Park
Service USFS Missoula Fire Science
Laboratory US DOE Global Change Education
Program Jeff Gaffney Milton Constantin LBNL
staff John McLaughlin and Jeff Aguiar
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Front half vs back half ATN
Punches from selected burn samples were sliced
into front and back halves and analyzed in an
attempt to characterize gasses adsorbed onto the
filter
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EGA measurement details
Sample heated in pure oxygen atmosphere
Only temperature and light transmission can be
used to make OC/EC split.
Constant heating rate of 40 C / minute
No temperature steps as seen in the IMPROVE and
NIOSH methods.
Light transmission measurement over entire
visible range
Use of white light and spectrometer gives light
transmission as a function of wavelength. Method
may aid OC/EC split determination if OC and
pyrolized OC has a different absorption
wavelength than EC.
Evolved C converted to CO2
Measured with LiCor CO2/H2O IR gas
analyzer Magnesium dioxide catalyst at 800 C
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Attenuation for selected burns (log)
flaming
smoldering