Measuring light absorption by freshly emitted organic aerosols: optical artifacts in traditional solvent-extraction-based methods

Recent studies have shown that organic aerosol (OA) could have a nontrivial role in atmospheric light absorption at shorter visible wavelengths. Good estimates of OA light absorption are therefore necessary to better estimate radiative forcing due to these aerosols in climate models. One of the comm...

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Bibliographic Details
Published in:Atmospheric chemistry and physics 2019-07, Vol.19 (13), p.8817-8830
Main Authors: Shetty, Nishit J, Pandey, Apoorva, Baker, Stephen, Hao, Wei Min, Chakrabarty, Rajan K
Format: Article
Language:English
Subjects:
Absorbance
Absorption
Absorption coefficient
Absorptivity
Acetone
Aerosol absorption
Aerosols
Air pollution
Albedo
Analysis
Atmospheric absorption
Atmospheric models
Bias
Biomass burning
Burning
Climate models
Dependence
Electromagnetic absorption
Light absorption
Measurement
Methanol
Methods
Organic carbon
Particulate matter
Photometry
Radiative forcing
Scaling
Scaling factors
Solvent extraction
Solvents
Spectrophotometers
Suspended particulate matter
Wavelengths
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Summary:Recent studies have shown that organic aerosol (OA) could have a nontrivial role in atmospheric light absorption at shorter visible wavelengths. Good estimates of OA light absorption are therefore necessary to better estimate radiative forcing due to these aerosols in climate models. One of the common techniques used to measure OA light absorption is the solvent extraction technique from filter samples which involves the use of a spectrophotometer to measure bulk absorbance by the solvent-soluble organic fraction of particulate matter. Measured solvent-phase absorbance is subsequently converted to particle-phase absorption coefficient using scaling factors. The conventional view is to apply a correction factor of 2 to absorption coefficients obtained from solvent-extracted OA based on Mie calculations. The appropriate scaling factors are a function of biases due to incomplete extraction of organic carbon (OC) by solvents and size-dependent absorption properties of OA. The range for these biases along with their potential dependence on burn conditions is an unexplored area of research.
ISSN:1680-7324
1680-7316
1680-7324
DOI:10.5194/acp-19-8817-2019