aerosol optical properties and biogenic soa: effect on ... · aerosol optical properties and...
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Aerosol Optical Properties and Biogenic SOA: Effect on Hygroscopic Properties and Light
Absorption
Andrey Khlystov (DRI), R. Subramanian (CMU)
Antonis Tasoglou, Spyros Pandis (CMU),
Provat Saha , Andrew Grieshop (NCSU),
Amara Holder, Mike Hays, John Walker (EPA)
83541101
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Two field measurement campaigns• Two SE US sites
characterized by different degrees of biogenic and anthropogenic influence
• Investigate influence of organic aerosol on aerosol optical properties
NO2 column density from OMI averaged for summer of 2010,derived using techniques described in Russell et al. (2010)
Centerville, AL, 1 June – 15 July 2013 Duke Forest (Chapel Hill, NC), 30 May – 26 June 2015
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Science questions / approach
• What is bSOA contribution to hygroscopic growth and light scattering
• What is bSOA contribution to light absorption
– Brown carbon
– “Lensing” effect
RH conditioningContribution to hygroscopic growth and light scattering, Bscat(RH)
Thermodenuder
200oC(and higher)
Contribution to light absorption: • Brown carbon (also from wavelength
dependence of Babs)• Lensing effect (Babs,coated> Babs, not-coated)
Measurements at 3 wavelengths:
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Measurement setup during SOAS
RH and temperature conditioning:• “Dry” line: < 20% RH• “Intermediate” line: ~60-70% RH• “High RH” line: > 85% RH• Thermodenuder (TD): 180 C or
scanning• Lines are switched every 15 min
Measured parameters:• Aerosol scattering and absorption
at 405nm, 532nm, 870nm• Single particle black carbon and
coating thickness• Particle size distribution above
70nm (only in July)
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Relative humidity cycles
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Measurement setup (Duke Forest)RH, T
RH > 80% (Wet 2)
RH > 50 - 70% (Wet 1)
RH < 20% (Dry)
Aurora 3000 3 wavelengthEcoTech Nephelometer
RH < 20% (Dry)
T <= 400oC (TD)
SMPS
SP2
DMA
Ambient air
PAX 405 & 532 nm
7 wavelengthAethalometer
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Centerville, AL 1 June – 15 July 2013
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Dry scattering during SOAS
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Scattering during different measurement cycles (SOAS)
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Effect of RH on light scattering
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The aerosol is wet below 80% RH(upper hysteresis curve)
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Gamma at “intermediate” RH is lower than at “high” RH
• The “intermediate” RH gamma is ~20% lower than “high” RH gamma.
• Could indicate partial deliquescence at either “intermediate” RH or that the gamma approximation does not work
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Effect of OA on light scattering enhancement due to RH (SOAS)
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“Dry” absorption from PAX (SOAS)
“Biomass” burning event
Very low light absorption:
Blue: 1.53 Mm-1
Green: 0.35 Mm-1*
Red: 0.49 Mm-1
*Green PAX data
unreliable (unstable laser power, background, etc.)
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Angstrom Absorption Exponent during SOAS
• Defines dependence of Babs on wavelength:
• Brown carbon is characterized by AAE > 2
• During SOAS average AAE = 1. 5 (blue/red)
• No clear indication of brown carbon
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Biomass burning on 6/4/2013
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AAE during 6/4/13 event is about 3, indicating presence of brown carbon
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Small particle losses in the TD
18
6/10/2015 6/11/2015 6/12/2015 6/13/2015 6/14/2015 6/15/2015 6/16/2015 6/17/2015 6/18/2015 6/19/2015
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
MF
RB
C-
SP
2
MFRBC, avg= 0.97 ± 0.09
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Contribution of semi-volatile species to light absorption (SOAS)
• Campaign-average Babs:Dry: 1.53 Mm-1
TD: 1.21 Mm-1
Suggests 26% enhancement
• Pairwise heated/dry measurements suggest that there is only 4% difference
Babs,dry / Babs,TD
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Duke Forest (Chapel Hill, NC) 30 May – 26 June 2015
Data evaluation is in progress and not yet ready for sharing
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Summary
21
• SOAS:
– OA had small to positive effect on humidity enhancementof light scattering, though very uncertain.
– With a few exceptions, no significant effect of OA on lightabsorption was observed (probably due to the very lowabsorption relative to uncertainties).
• Duke Forest:
– Measurements are completed, data evaluation is inprogress
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