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| Titel |
Impacts of volatilisation on light scattering and filter-based absorption measurements: a case study |
| VerfasserIn |
J. Backman, A. Virkkula, T. Petäjä, M. Aurela, A. Frey, R. Hillamo |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1867-1381
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Measurement Techniques ; 3, no. 5 ; Nr. 3, no. 5 (2010-09-06), S.1205-1216 |
| Datensatznummer |
250001286
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| Publikation (Nr.) |
 copernicus.org/amt-3-1205-2010.pdf |
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| Zusammenfassung |
Aerosol light absorption measurements most commonly rely on filter-based
techniques. These methods are influenced by light scattering
constituents in the aerosol phase deposited on the filters. The coating of
soot by non-absorbing constituents changes the mixing state of soot as
the aerosol ages and increase light absorption by the aerosol. Most light
scattering constituents in a sub-micron aerosol are volatile by their
nature due to their chemical composition and can be volatilized by
heating the sample air. The initial mixing state is lost but the remaining light
absorption by the aerosol should be by non-coated soot alone.
This was studied during a short field campaign with two groups of equipment
measuring in parallel for six days in April 2009 at the SMEAR III station in
Helsinki. When heated, the light scattering constituents were evaporated
thus reducing the single-scattering albedo (ω0) of the aerosol
by as much as 0.4. An oven was set to scan different temperatures which revealed the volatility
of the urban aerosol at different temperatures as well as the single-scattering
albedo's dependence on the non-volatile volume fraction remaining (NVFR).
The NVFR was 0.72 ± 0.13, 0.42 ± 0.06 and 0.22 ± 0.05 at
50, 150 and 280 °C respectively. ω0 behaved analogically,
it was 0.71 ± 0.05, 0.62 ± 0.06 and 0.42 ± 0.07 at the respective
temperatures. We found that absorption coefficients measured at different
temperatures showed a temperature dependency possibly indicating initially
different mixing states of the non-volatile constituents.
By heating the aerosol
the mode of the size distribution gets shifted to smaller sizes which in turn
changes the filter-based instrument's response due increased penetration
depth into the filter by the smaller residual particles. This was compensated
for by using size distribution data. |
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