Visible light absorption by organic carbon during FLAME
Preliminary results from spectral characterization of aerosol absorption during FLAME Colorado State University University of Nevada/DRI Gavin McMeeking Pat Arnott Sonia Kreidenweis Kristin Lewis Jeffrey Collett, Jr. Lawrence Berkeley NL
Lynn Rinehart Melissa Lunden US Forest Service Cyle Wold Guenter Engling Thomas Kirchstetter Patrick Freeborn Rich Cullin Kip Carrico October 30, 2006 Group meeting Biomass burning climate effects
Focus of this work Biomass burning visibility effects Focus of this work adapted from Malm et al. (2004) Classifying carbon Terms describing carbonaceous aerosol are defined from how each is measured and used
Light Absorbing Carbon Chemical structure controls light absorption (electrons are highly mobile in EC/BC) Evidence of visible light absorption by organic carbon ndreae and Gelencser, 2006 (AG06) rown carbon: Light-absorbing organic matter in atmospheric aerosols of various
rigins soil humics, HULIS, tarry materials from combustion, bioaerosols tterson and McMahon, 1984 and Bond, 2001 Observed smoldering material and residential coal combustion can contain arge amounts of Cbrown Kirchstetter et al, 2004 Demonstrated an OC contribution to spectral light absorption for several biomass rom SAFARI same technique used in this study
et al., 2005, Havers et al., 1998, Gelencser et al. 2000 and o Fine continental aerosol contains organic carbon with properties similar to natura humic/fulvic substances. Andreae and Crutzen, 1997 Biogenic materials and their oxidation and polymerization products can absorb lig 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 assumed Tropospheric photochemistry for soot. 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.
oud 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. Impacts of Cbrown (AG06) Thermochemical analysis Significant contributions of Cbrown to tropospheric fine aerosol could bias traditional measurement techniques that are carried on to calculations of light
absorption. Cbrown is volatilized over a wide range of temperatures and may be classified partly as OC and partly as EC (Mayol-Bracero et al., 2002). Biomass smoke contains inorganic components that catalyze oxidation of soot and Cbrown, resulting in lower evolution temperatures (Novakov and Corrigan, 1995). Experimental setup for FLAME May/June 2006
Filter samplers for chamber burns Hi Vol IMPROVE Biomass types burned during FLAME (chamber) Lawrence Berkeley Lab visit September/October 2006
Visible light attenuation measurements Light box Ten LED light source Spectrometer (Ocean Optics S2000) 400 1100 nm range with sub nanometer resolution
Attenuation calculation 1 ATN 100ln T Attenuation Transmission Sample intensity
I s I r ,o T I s,o I r Reference filter intensities Sample filter intensity Attenuation spectral dependence (Bohren and Huffman, small particles) : constant
attenuation exponent assumed = 1 for EC ATN K wavelength Untreated ATN measurements Base case measurement
of filter attenuation as a function of wavelength Measured for all burns AS on at least one 1.14 cm2 punch from B HiVol quartz filter sample (PM2.5) Ceanothus HiVol sample Normalized light ATN for selected burns Absorption exponent ranged from 0.8 (chamise, lignin) to
~ 3.5 (Alaskan duff, rice straw) ATN base case results 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
Filter solvent treatments Puerto Rican mixed woods No treatment Acetone extraction Filter treatments: Lodgepole Pine (normalized) water extraction results in no change
water extraction results in largest reduction 3.1 2.3 1.0 Filter treatments: Alaskan duff very weak attenuation by back half of filter Total carbon measurements: Evolved Gas Analysis (EGA)
Total carbon measurements: Evolved Gas Analysis (EGA) to CO2 analyzer light source fan fiber optic to spectromete r
sample oven catalyst oven O2 carrier gas light collector EGA light source upgrade solid quartz tube
brighter light source filter holder Example EGA (no treatment) Burn B, chamise - flaming combustion - Low OC/EC ratio EC attenuation at 544 nm
OC Example EGA (no treatment) Burn P, southern pine - mixed combustion OC EC slight increase
due to oven heat pyrolized carbon ATN Example EGA (no treatment) Burn G, Alaskan duff - Smoldering combustion - High OC/EC ratio OC no EC?
pyrolized carbon ATN Attenuation coefficients Attenuation divided by total carbon mass How will results change when ATN divided by EGA-determined OC and EC? Effect of solvent treatments on EGA
Front/back half filter EGA results Burn L, lodgepole pine - mixed combustion whole filter (26 ug cm-2) front half (20.5 ug cm-2) back half (5.1 ug cm-2) EGA spectrometer measurements
Burn M, PR fern - mixed combustion oven signal No attenuation Large change in ATN (EC evolving here) charring EGA spectrometer measurements Burn G, Alaskan duff
- smoldering combustion - very little EC oven signal No attenuation No large ATN change as seen in PR fern charring 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 Attenuation Work to be done
- 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 Evolved gas analysis -- Compare results otherdetermination studies (fresh to vs.Sunset
aged smoke?) Compare FLAME EGA results fortoOC/EC analyzer -- Develop method to deconvolute attenuation into brown and Analyze spectrometer measurements
taken during EGA carbon runs and try to black carbon components determine optical properties of pyrolized carbon 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 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 EGA measurement details ample heated in pure oxygen atmosphere Only temperature and light transmission can be used to make OC/EC split. onstant heating rate of 40 C / minute No temperature steps as seen in the IMPROVE and NIOSH methods.
t 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 Attenuation for selected burns (log)
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