I am getting decrease of absorption enhancement during aging of biomass burning aerosol. Nothing help on looking size distribution data. Can anyone explain to me why such happening?
Would you please provide more details on the measurements of absorption?
Your question is vague.
Did you mean 'decrease in the enhancement' of absorption in aged bio-mass burning aerosols? That is, you made a spectral absorption measurement, and the spectral steepness decreased with aging of the aerosols?
If so, it is possible that in fresh biomass burning the organic (brown) carbon content would be significant leading to a steeper absorption spectrum. As the aerosol ages, these are chemically and physically transformed and get mixed with other aerosol types, which would reduce its absorptivity in the blue (short wavelength regime) and this would manifest as a decrease in the spectral steepness.
@ Moorthy & Zhang: Let me clear about my question.
Actually we measured absorption due to biomass smoke in dry phase and after thermal denuded at blue and red wavelengths. Our plan was try to differentiated black and Brown carbon absorption. We calculated absorption enhancement by comparing dry and denuded absorption. But in our chamber study absorption enhancement gets lower on aging. Our plan was to measured effect of SOA formation on aging and its effect on absorption enhancement (with initial guess increase in absorption enhancement). We analyze size distribution also but did not help to explain. Can you guys help me to figured that out why we are getting such interesting facts?
How did you measure the size distribution? AT what interval? for how long? and in what particle size regime?
What instrument was used?
did you cover the nucleation size regime ?
How is the trend for the absolute absorption for dry and denuded particles? Is it possible that the formed SOA are absorptive like Brown carbon?
@ Moorthy
we used SMPS to measured volume and number distribution in the particles size regime of 10.9-478.3 nm. Yes our measurement cover nucleation size regime and we observed nice nucleation( banana shape nucleation structure).
@ Zhang
We observed mixed pattern of dry and denuded absorption (increasing ,decreasing) on different perturbation we used ( like ozone,Nox, exposed of UV etc). Our expectation was SOA are like Brown or something but what we observed is different.
Hi,
very interesting in my opinion.
it is possible that by aging the aerosols, your actually reduce the light absorption, since your aging process increase the O/C ratio and breaks down the double bonds which are responsible to the absorption in the visible range. sometime people call this aging that cause a reduction in the absorption as ''bleaching''.
To support this assumption, you need to conduct detailed chemical analysis of your precursors and SOA. if you got This is not an easy task but it is definitely interesting and a hot topic.
Aging means removal of particles because of settling, because of coagulation, because of was and/or rain out. Obviously those processes remove absorbing particles in your case. Are you certain, that your size Distribution is not changing during aging?
Very interesting thought by Avi
But in this case the signal in the UV channel should be decreasing. At the other lambdas the absorption is more du to inert EC/BC
@Rudra
Does the decrease in light absorption depend on the wavelength of the aethalometer?
This question is directly related to my comment to the idea in the reply by Avi Lavi.
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