Preliminary results from spectral characterization of aerosol absorption during FLAME

1. 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 Lawrence Berkeley NL US Forest Service Melissa Lunden Thomas Kirchstetter Cyle Wold Patrick Freeborn October 30, 2006 – Group meeting

2. Biomass burning climate effects Focus of this work

3. Biomass burning visibility effects Focus of this work adapted from Malm et al. (2004)

4. 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

5. 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

6. 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.

7. 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).

8. Experimental setup for FLAME May/June 2006

9. Filter samplers for chamber burns IMPROVE Hi Vol

10. Biomass types burned during FLAME (chamber)

11. Lawrence Berkeley Lab visit September/October 2006

12. 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

13. 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

14. 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

15. Normalized light ATN for selected burns Absorption exponent ranged from 0.8 (chamise, lignin) to ~ 3.5 (Alaskan duff, rice straw)

16. ATN base case results Kirchstetter et al., 2004

17. 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

18. Filter solvent treatments Puerto Rican mixed woods No treatment Acetone extraction

19. Filter treatments: Lodgepole Pine water extraction results in no change (normalized) ~ 1.5 1.0 0.9 acetone extraction reduces attenuation coefficient

20. 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

21. Filter treatments: Alaskan duff very weak attenuation by back half of filter

22. Total carbon measurements:Evolved Gas Analysis (EGA)

23. Total carbon measurements:Evolved Gas Analysis (EGA) to CO2 analyzer light source fiber optic to spectrometer fan sample oven catalyst oven light collector O2 carrier gas

24. EGA light source upgrade solid quartz tube filter holder brighter light source

25. Example EGA (no treatment) Burn B, chamise - flaming combustion - Low OC/EC ratio EC attenuation at 544 nm OC

26. Example EGA (no treatment) Burn P, southern pine - mixed combustion OC EC slight increasedue to oven heat pyrolized carbon ATN

27. Example EGA (no treatment) Burn G, Alaskan duff • Smoldering combustion • High OC/EC ratio OC no EC? pyrolized carbon ATN

28. 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

29. Effect of solvent treatments on EGA

30. 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)

31. EGA spectrometer measurements Burn M, PR fern - mixed combustion oven signal No attenuation Large change in ATN(EC evolving here) ‘charring’

32. 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’

33. 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

34. 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

35. 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

36. 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

37. 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

38. Attenuation for selected burns (log) flaming smoldering