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 Melissa Lunden Thomas Kirchstetter Pat Arnott Kristin Lewis Cyle Wold Patrick Freeborn Colorado State University Lawrence Berkeley NL University of Nevada/DRI US Forest Service 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 Light Absorbing Carbon Chemical structure controls light absorption (electrons are highly mobile in EC/BC)

5. Evidence of visible light absorption by organic carbon Brown carbon: Light-absorbing organic matter in atmospheric aerosols of various origins – soil humics, HULIS, tarry materials from combustion, bioaerosols Andreae and Gelencser, 2006 (AG06) Kirchstetter et al, 2004 Hoffer et al., 2005, Havers et al., 1998, Gelencser et al. 2000 and others Patterson and McMahon, 1984 and Bond, 2001 Observed smoldering material and residential coal combustion can contain large amounts of C brown Demonstrated an OC contribution to spectral light absorption for several biomass from SAFARI – same technique used in this study Andreae and Crutzen, 1997 Biogenic materials and their oxidation and polymerization products can absorb light Fine continental aerosol contains organic carbon with properties similar to natural humic/fulvic substances.

6. Impacts of C brown (AG06) The presence of C brown 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 measurements 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. Tropospheric photochemistry If a significant fraction of C brown 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

7. Impacts of C brown (AG06) Significant contributions of C brown to tropospheric fine aerosol could bias traditional measurement techniques that are carried on to calculations of light absorption. C brown 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 C brown, resulting in lower evolution temperatures (Novakov and Corrigan, 1995). Not known if C brown 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

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 Kirchstetter et al., 2004 Light box 400 – 1100 nm range with sub nanometer resolution Spectrometer (Ocean Optics S2000) Ten LED light source

13. Attenuation calculation Attenuation Transmission Sample intensity Sample filter intensity Reference filter intensities wavelength attenuation exponent assumed = 1 for EC constant Attenuation spectral dependence (Bohren and Huffman, small particles) :

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 cm 2 punch from “B” HiVol quartz filter sample (PM 2.5 ) 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 0.9 ~ 1.5 acetone extraction reduces attenuation coefficient 1.0 (normalized)

20. Filter treatments: Alaskan duff 1.0 2.3 3.5 3.1 water extraction results in largest reduction hexane extraction results in increase (normalized only)

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

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

23. to CO 2 analyzer O 2 carrier gas light source sample oven catalyst oven light collector fiber optic to spectrometer fan

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

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

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

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

28. Attenuation coefficients Kirchstetter et al., 2004 Attenuation divided by total carbon mass How will results change when ATN divided by EGA-determined OC and EC?

29. Effect of solvent treatments on EGA

30. Front/back half filter EGA results whole 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

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

32. EGA spectrometer measurements No attenuation ‘charring’ Burn G, Alaskan duff - smoldering combustion - very little EC No large ATN change as seen in PR fern oven signal

33. 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. Attenuation Kirchstetter et al., 2004 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

34. 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 components Attenuation Kirchstetter et al., 2004 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

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 Only temperature and light transmission can be used to make OC/EC split. Sample heated in pure oxygen atmosphere No temperature steps as seen in the IMPROVE and NIOSH methods. Constant heating rate of 40 C / minute 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. Light transmission measurement over entire visible range Measured with LiCor CO 2 /H 2 O IR gas analyzer Magnesium dioxide catalyst at 800 C Evolved C converted to CO 2

38. Attenuation for selected burns (log) smoldering flaming