Measuring light absorption by freshly emitted organic aerosols: optical artifacts in traditional solvent-extraction-based methods
<p>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...
| Main Authors: | , , , , |
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| Format: | Article |
| Language: | English |
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Copernicus Publications
2019-07-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://www.atmos-chem-phys.net/19/8817/2019/acp-19-8817-2019.pdf |
| _version_ | 1818131885389250560 |
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| author | N. J. Shetty A. Pandey S. Baker W. M. Hao R. K. Chakrabarty R. K. Chakrabarty |
| author_facet | N. J. Shetty A. Pandey S. Baker W. M. Hao R. K. Chakrabarty R. K. Chakrabarty |
| author_sort | N. J. Shetty |
| collection | DOAJ |
| description | <p>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.</p>
<p>Here, we performed a comprehensive laboratory study involving three solvents
(water, methanol, and acetone) to investigate the bias in absorption
coefficients obtained from solvent-extraction-based photometry techniques as
compared to in situ particle-phase absorption for freshly emitted OA from
biomass burning. We correlated the bias with <span class="inline-formula">OC∕TC</span> (total carbon) mass ratio and single
scattering albedo (SSA) and observed that the conventionally used correction
factor of 2 for water and methanol-extracted OA might not be extensible to
all systems, and we suggest caution while using such correction factors to
estimate particle-phase OA absorption coefficients. Furthermore, a linear
correlation between SSA and the <span class="inline-formula">OC∕TC</span> ratio was also established. Finally, from
the spectroscopic data, we analyzed the differences in absorption
Ångström exponents (AÅE) obtained from solution- and
particulate-phase measurements. We noted that AÅE from
solvent-phase measurements could deviate significantly from their OA
counterparts.</p> |
| first_indexed | 2024-12-11T08:28:02Z |
| format | Article |
| id | doaj.art-3da69422f39c4177bb7d07c84b70e468 |
| institution | Directory Open Access Journal |
| issn | 1680-7316 1680-7324 |
| language | English |
| last_indexed | 2024-12-11T08:28:02Z |
| publishDate | 2019-07-01 |
| publisher | Copernicus Publications |
| record_format | Article |
| series | Atmospheric Chemistry and Physics |
| spelling | doaj.art-3da69422f39c4177bb7d07c84b70e4682022-12-22T01:14:31ZengCopernicus PublicationsAtmospheric Chemistry and Physics1680-73161680-73242019-07-01198817883010.5194/acp-19-8817-2019Measuring light absorption by freshly emitted organic aerosols: optical artifacts in traditional solvent-extraction-based methodsN. J. Shetty0A. Pandey1S. Baker2W. M. Hao3R. K. Chakrabarty4R. K. Chakrabarty5Center for Aerosol Science and Engineering, Department of Energy, Environmental and Chemical Engineering, Washington University in St. Louis, St. Louis, MO 63130, USACenter for Aerosol Science and Engineering, Department of Energy, Environmental and Chemical Engineering, Washington University in St. Louis, St. Louis, MO 63130, USAUSDA Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory, Missoula, Montana, USAUSDA Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory, Missoula, Montana, USACenter for Aerosol Science and Engineering, Department of Energy, Environmental and Chemical Engineering, Washington University in St. Louis, St. Louis, MO 63130, USAMcDonnell Center for the Space Sciences, Washington University in St. Louis, St. Louis, MO 63130, USA<p>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.</p> <p>Here, we performed a comprehensive laboratory study involving three solvents (water, methanol, and acetone) to investigate the bias in absorption coefficients obtained from solvent-extraction-based photometry techniques as compared to in situ particle-phase absorption for freshly emitted OA from biomass burning. We correlated the bias with <span class="inline-formula">OC∕TC</span> (total carbon) mass ratio and single scattering albedo (SSA) and observed that the conventionally used correction factor of 2 for water and methanol-extracted OA might not be extensible to all systems, and we suggest caution while using such correction factors to estimate particle-phase OA absorption coefficients. Furthermore, a linear correlation between SSA and the <span class="inline-formula">OC∕TC</span> ratio was also established. Finally, from the spectroscopic data, we analyzed the differences in absorption Ångström exponents (AÅE) obtained from solution- and particulate-phase measurements. We noted that AÅE from solvent-phase measurements could deviate significantly from their OA counterparts.</p>https://www.atmos-chem-phys.net/19/8817/2019/acp-19-8817-2019.pdf |
| spellingShingle | N. J. Shetty A. Pandey S. Baker W. M. Hao R. K. Chakrabarty R. K. Chakrabarty Measuring light absorption by freshly emitted organic aerosols: optical artifacts in traditional solvent-extraction-based methods Atmospheric Chemistry and Physics |
| title | Measuring light absorption by freshly emitted organic aerosols: optical artifacts in traditional solvent-extraction-based methods |
| title_full | Measuring light absorption by freshly emitted organic aerosols: optical artifacts in traditional solvent-extraction-based methods |
| title_fullStr | Measuring light absorption by freshly emitted organic aerosols: optical artifacts in traditional solvent-extraction-based methods |
| title_full_unstemmed | Measuring light absorption by freshly emitted organic aerosols: optical artifacts in traditional solvent-extraction-based methods |
| title_short | Measuring light absorption by freshly emitted organic aerosols: optical artifacts in traditional solvent-extraction-based methods |
| title_sort | measuring light absorption by freshly emitted organic aerosols optical artifacts in traditional solvent extraction based methods |
| url | https://www.atmos-chem-phys.net/19/8817/2019/acp-19-8817-2019.pdf |
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