preliminary results from spectral characterization of aerosol absorption during flame

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Preliminary results from spectral characterization of aerosol absorption during FLAME. Gavin McMeeking Sonia Kreidenweis Jeffrey Collett, Jr. Lynn Rinehart Guenter Engling Rich Cullin Kip Carrico. Colorado State University. University of Nevada/DRI. Pat Arnott Kristin Lewis. - PowerPoint PPT Presentation


  • Preliminary results from spectral characterization of aerosol absorption during FLAMEGavin McMeekingSonia KreidenweisJeffrey Collett, Jr.Lynn RinehartGuenter EnglingRich CullinKip CarricoMelissa LundenThomas KirchstetterPat ArnottKristin LewisCyle WoldPatrick FreebornColorado State UniversityLawrence Berkeley NLUniversity of Nevada/DRIUS Forest ServiceOctober 30, 2006 Group meeting

  • Biomass burning climate effectsFocus of this work

  • Biomass burning visibility effectsFocus of this workadapted from Malm et al. (2004)

  • Classifying carbonTerms describing carbonaceous aerosol are defined from how each is measured and usedLight Absorbing CarbonChemical structure controls light absorption (electrons are highly mobile in EC/BC)

  • Evidence of visible light absorption by organic carbonBrown carbon: Light-absorbing organic matter in atmospheric aerosols of various origins soil humics, HULIS, tarry materials from combustion, bioaerosolsAndreae and Gelencser, 2006 (AG06)Kirchstetter et al, 2004Hoffer et al., 2005, Havers et al., 1998, Gelencser et al. 2000 and others

    Patterson and McMahon, 1984 and Bond, 2001Observed smoldering material and residential coal combustion can contain large amounts of CbrownDemonstrated an OC contribution to spectral light absorption for several biomass from SAFARI same technique used in this studyAndreae and Crutzen, 1997Biogenic materials and their oxidation and polymerization products can absorb lightFine continental aerosol contains organic carbon with properties similar to natural humic/fulvic substances.

  • Impacts of Cbrown (AG06)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 for soot.

    Light absorption measurementsCare 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.

    Tropospheric photochemistryIf 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.

    Cloud chemistry and cloud light absorption

  • Impacts of Cbrown (AG06)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).

    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 and laboratory-generated soot samples (Chow et al., 2001).

    Thermochemical analysis

  • Experimental setup for FLAMEMay/June 2006

  • Filter samplers for chamber burnsIMPROVEHi Vol

  • Biomass types burned during FLAME (chamber)

  • Lawrence Berkeley Lab visitSeptember/October 2006

  • Visible light attenuation measurementsKirchstetter et al., 2004Light box400 1100 nm range with sub nanometer resolution Spectrometer (Ocean Optics S2000)Ten LED light source

  • Attenuation calculationAttenuationTransmissionSample intensitySample filter intensityReference filter intensitieswavelengthattenuation exponentassumed = 1 for ECconstantAttenuation spectral dependence (Bohren and Huffman, small particles) :

  • Untreated ATN measurementsBase case measurement of filter attenuation as a function of wavelengthMeasured for all burns A-S on at least one 1.14 cm2 punch from B HiVol quartz filter sample (PM2.5)Ceanothus HiVol sample

  • Normalized light ATN for selected burnsAbsorption exponent ranged from 0.8 (chamise, lignin) to ~ 3.5 (Alaskan duff, rice straw)

  • ATN base case resultsKirchstetter et al., 2004

  • Filter solvent treatmentsSelected filter samples were extracted with hexane, acetone and water to determine role of organic carbon and water soluble carbon on filter attenuationEach organic solvent extraction was performed for ~ one hour and water extraction for 12 hours

  • Filter solvent treatmentsPuerto Rican mixed woodsNo treatmentAcetone extraction

  • Filter treatments: Lodgepole Pinewater extraction results in no change0.9~ 1.5acetone extraction reduces attenuation coefficient1.0(normalized)

  • Filter treatments: Alaskan duff1. extraction results in largest reductionhexane extraction results in increase (normalized only)

  • Filter treatments: Alaskan duffvery weak attenuation by back half of filter

  • Total carbon measurements:Evolved Gas Analysis (EGA)

  • Total carbon measurements:Evolved Gas Analysis (EGA)to CO2 analyzerO2 carrier gaslight sourcesample ovencatalyst ovenlight collectorfiber optic to spectrometerfan

  • EGA light source upgradefilter holderbrighter light sourcesolid quartz tube

  • Example EGA (no treatment)Burn B, chamiseECOCattenuation at 544 nm- flaming combustion- Low OC/EC ratio

  • Example EGA (no treatment)Burn P, southern pineECOCpyrolized carbon ATN- mixed combustionslight increase due to oven heat

  • Example EGA (no treatment)Burn G, Alaskan duffno EC?OCpyrolized carbon ATN Smoldering combustion High OC/EC ratio

  • Attenuation coefficientsKirchstetter et al., 2004Attenuation divided by total carbon massHow will results change when ATN divided by EGA-determined OC and EC?

  • Effect of solvent treatments on EGA

  • Front/back half filter EGA resultswhole filter (26 ug cm-2) front half (20.5 ug cm-2)back half (5.1 ug cm-2)Burn L, lodgepole pine- mixed combustion

  • EGA spectrometer measurementsNo attenuationcharringBurn M, PR fern- mixed combustionLarge change in ATN (EC evolving here)oven signal

  • EGA spectrometer measurementsNo attenuationcharringBurn G, Alaskan duff- smoldering combustion- very little ECNo large ATN change as seen in PR fernoven signal

  • Summary of work done so far 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.AttenuationKirchstetter et al., 2004Evolved 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

  • 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 Compare FLAME results to other studies (fresh vs. aged smoke?) Develop method to deconvolute attenuation into brown carbon and black carbon componentsAttenuationKirchstetter et al., 2004Evolved 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

  • AcknowledgementsJoint Fire Science ProgramNational Park ServiceUSFS Missoula Fire Science LaboratoryUS DOE Global Change Education ProgramJeff GaffneyMilton ConstantinLBNL staffJohn McLaughlin and Jeff Aguiar

  • Front half vs back half ATNPunches 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 detailsOnly temperature and light transmission can be used to make OC/EC split.

    Sample heated in pure oxygen atmosphereNo temperature steps as seen in the IMPROVE and NIOSH methods.

    Constant heating rate of 40 C / minuteUse 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.

    Light transmission measurement over entire visible rangeMeasured with LiCor CO2/H2O IR gas analyzerMagnesium dioxide catalyst at 800 C

    Evolved C converted to CO2

  • Attenuation for selected burns (log)smolderingflaming


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