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| Titel |
Ambient black carbon particle hygroscopic properties controlled by mixing state and composition |
| VerfasserIn |
D. Liu, J. Allan, J. Whitehead, D. Young, M. Flynn, H. Coe, G. McFiggans, Z. L. Fleming, B. Bandy |
| 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. 4 ; Nr. 13, no. 4 (2013-02-21), S.2015-2029 |
| Datensatznummer |
250018422
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| Publikation (Nr.) |
 copernicus.org/acp-13-2015-2013.pdf |
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| Zusammenfassung |
| The wet removal of black carbon aerosol (BC) in the atmosphere is a crucial
factor in determining its atmospheric lifetime and thereby the vertical and
horizontal distributions, dispersion on local and regional scales, and the
direct, semi-direct and indirect radiative forcing effects. The in-cloud
scavenging and wet deposition rate of freshly emitted hydrophobic BC will be
increased on acquisition of more-hydrophilic components by coagulation or
coating processes. The lifetime of BC is still subject to considerable
uncertainty for most of the model inputs, which is largely due to the
insufficient constraints on the BC hydrophobic-to-hydrophilic conversion
process from observational field data. This study was conducted at a site
along UK North Norfolk coastline, where the BC particles were transported
from different regions within Western Europe. A hygroscopicity tandem
differential mobility analyser (HTDMA) was coupled with a single particle
soot photometer (SP2) to measure the hygroscopic properties of BC particles
and associated mixing state in real time. In addition, a Soot Particle AMS
(SP-AMS) measured the chemical compositions of additional material associated
with BC particles. The ensemble of BC particles persistently contained a
less-hygroscopic mode at a growth factor (gf) of around 1.05 at 90% RH
(dry diameter 163 nm). Importantly, a more-hygroscopic mode of BC particles
was observed throughout the experiment, the gf of these BC particles extended
up to ~1.4–1.6 with the minimum between this and the less hygroscopic
mode at a gf ~1.25, or equivalent effective hygroscopicity parameter
κ ~0.1. The gf of BC particles (gfBC) was highly
influenced by the composition of associated soluble material: increases of
gfBC were associated with secondary inorganic components, and these
increases were more pronounced when ammonium nitrate was in the BC particles;
however the presence of secondary organic matter suppressed the gfBC
below that of pure inorganics. The Zdanovskii-Stokes-Robinson (ZSR) mixing
rule captures the hygroscopicity contributions from different compositions
within ±30% compared to the measured results, however is subject to
uncertainty due to the complex morphology of BC component and potential
artefacts associated with semivolatile particles measured with the HTDMA.
This study provides detailed insights on BC hygroscopicity associated with
its mixing state, and the results will importantly constrain the
microphysical mixing schemes of BC as used by a variety of high level models.
In particular, this provides direct evidence to highlight the need to
consider ammonium nitrate ageing of BC particles because this will result in
particles becoming hydrophilic on much shorter timescales than for sulphate
formation, which is often the only mechanism considered. |
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