preliminary results from spectral characterization of aerosol absorption during flame gavin...

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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 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

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Preliminary results from spectral characterization of aerosol absorption during FLAME

Gavin McMeekingSonia KreidenweisJeffrey Collett, Jr.

Lynn RinehartGuenter Engling

Rich CullinKip Carrico

Melissa LundenThomas Kirchstetter

Pat ArnottKristin Lewis

Cyle WoldPatrick Freeborn

Colorado State University

Lawrence Berkeley NL

University of Nevada/DRI

US Forest Service

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 carbonTerms describing carbonaceous aerosol are defined from how each is measured and used

Light

Abso

rbin

g C

arb

on

Chemical structure controls light absorption (electrons are highly mobile in EC/BC)

Evidence of visible light absorption by organic carbon

Brown carbon: Light-absorbing organic matter in atmospheric aerosols of variousorigins – 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, 2001Observed smoldering material and residential coal combustion can contain large amounts of Cbrown

Demonstrated an OC contribution to spectral light absorption for several biomass from SAFARI – same technique used in this study

Andreae and Crutzen, 1997Biogenic materials and their oxidation and polymerization products can absorb light

Fine continental aerosol contains organic carbon with properties similar to naturalhumic/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 assumedfor 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 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 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).

Thermochemical analysis

Experimental setup for FLAMEMay/June 2006

Filter samplers for chamber burns

IMPROVEHi Vol

Biomass types burned during FLAME (chamber)

Lawrence Berkeley Lab visitSeptember/October 2006

Visible light attenuation measurements

Light box

400 – 1100 nm range with sub nanometer resolution

Spectrometer(Ocean Optics S2000)

Ten LED light source

Attenuation calculation

TATN

1ln100

r

or

os

s

I

I

II

T ,

,

Attenuation Transmission

Sample intensity

Sample filter intensity

Reference filter intensities

βλKATN wavelength

attenuation exponentassumed = 1 for EC

constant

Attenuation spectral dependence (Bohren and Huffman, small particles) :

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

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 treatmentsSelected 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

water extraction results in no change

0.9

~ 1.5

acetone extraction reduces attenuation coefficient

1.0

(norm

aliz

ed)

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)

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

O2 carrier gas

light source

sample oven catalyst oven

light collector

fiber optic to spectromete

r

fan

EGA light source upgrade

filter holder

brighter light source

solid quartz tube

Example EGA (no treatment)

Burn B, chamise

EC

OC

attenuation at 544 nm

- flaming combustion- Low OC/EC ratio

Example EGA (no treatment)

Burn P, southern pine

ECOC

pyrolized carbon ATN

- mixed combustion

slight increasedue to oven heat

Example EGA (no treatment)

Burn G, Alaskan duff

no EC?

OC

pyrolized carbon ATN

- Smoldering combustion- High OC/EC ratio

Attenuation coefficientsAttenuation 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

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

EGA spectrometer measurements

No attenuation

‘charring’

Burn M, PR fern- mixed combustion

Large change in ATN(EC evolving here)

oven signal

EGA spectrometer measurements

No attenuation

‘charring’

Burn G, Alaskan duff- smoldering combustion- very little EC

No large ATN changeas seen in PR fern

oven 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.

Attenuation

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

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

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

Acknowledgements

Joint Fire Science ProgramNational Park Service

USFS – Missoula Fire Science LaboratoryUS DOE Global Change Education Program

Jeff GaffneyMilton Constantin

LBNL staffJohn 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

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 CO2/H2O IR gas analyzerMagnesium dioxide catalyst at 800 C

Evolved C converted to CO2

Attenuation for selected burns (log)

smoldering

flaming