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| Titel |
Water uptake is independent of the inferred composition of secondary aerosols derived from multiple biogenic VOCs |
| VerfasserIn |
M. R. Alfarra, N. Good, K. P. Wyche, J. F. Hamilton, P. S. Monks, A. C. Lewis, G. McFiggans |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1680-7316
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 13, no. 23 ; Nr. 13, no. 23 (2013-12-04), S.11769-11789 |
| Datensatznummer |
250085855
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| Publikation (Nr.) |
 copernicus.org/acp-13-11769-2013.pdf |
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| Zusammenfassung |
| We demonstrate that the water uptake properties derived from sub- and
super-saturated measurements of chamber-generated biogenic secondary organic
aerosol (SOA) particles are independent of their degree of oxidation,
determined using both online and offline methods. SOA particles are formed
from the photooxidation of five structurally different biogenic VOCs,
representing a broad range of emitted species and their corresponding range
of chemical reactivity: α-pinene, β-caryophyllene, limonene,
myrcene and linalool. The fractional contribution of mass fragment 44 to the
total organic signal (f44) is used to characterise the extent of
oxidation of the formed SOA as measured online by an aerosol mass
spectrometer. Results illustrate that the values of f44 are dependent on
the precursor, the extent of photochemical ageing as well as on the initial
experimental conditions. SOA generated from a single biogenic precursor
should therefore not be used as a general proxy for biogenic SOA. Similarly,
the generated SOA particles exhibit a range of hygroscopic properties,
depending on the precursor, its initial mixing ratio and photochemical
ageing. The activation behaviour of the formed SOA particles show no temporal
trends with photochemical ageing. The average κ values derived from
the HTDMA and CCNc are generally found to cover the same range for each
precursor under two different initial mixing ratio conditions. A positive
correlation is observed between the hygroscopicity of particles of a single
size and f44 for α-pinene, β-caryophyllene, linalool and
myrcene, but not for limonene SOA. The investigation of the generality of
this relationship reveals that α-pinene, limonene, linalool and
myrcene are all able to generate particles with similar hygroscopicity
(κHTDMA ~0.1) despite f44 exhibiting a
relatively wide range of values (~4 to 11%). Similarly,
κCCN is found to be independent of f44. The same
findings are also true when sub- and super-saturated water uptake properties
of SOA are compared to the averaged carbon oxidation state
(OSC) determined using an offline method. These
findings do not necessarily suggest that water uptake and chemical
composition are not related. Instead, they suggest that either f44 and
OSC do not represent the main dominant
composition-related factors controlling water uptake of SOA particles, or
they may emphasise the possible impact of semi-volatile compounds on limiting
the ability of current state-of-the-art techniques to determine the chemical
composition and water uptake properties of aerosol particles. |
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