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| Titel |
The optical, physical and chemical properties of the products of glyoxal uptake on ammonium sulfate seed aerosols |
| VerfasserIn |
M. Trainic, A. Abo Riziq, A. Lavi, J. M. Flores, Y. Rudich |
| 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 ; 11, no. 18 ; Nr. 11, no. 18 (2011-09-20), S.9697-9707 |
| Datensatznummer |
250010089
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| Publikation (Nr.) |
 copernicus.org/acp-11-9697-2011.pdf |
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| Zusammenfassung |
| The heterogeneous reaction between gas phase glyoxal and ammonium sulfate
(AS) aerosols, a proxy for inorganic atmospheric aerosol, was studied in
terms of the dependence of the optical, physical and chemical properties of
the product aerosols on initial particle size and ambient relative humidity
(RH). Our experiments imitate an atmospheric scenario of a dry particle
hydration at ambient RH conditions in the presence of glyoxal gas followed
by efflorescence due to decrease of the ambient RH. The reactions were
studied under different RH conditions, starting from dry conditions (~20% RH) and up to 90% RH, covering conditions prevalent in many
atmospheric environments, and followed by consequent drying of the reacted
particles before their analysis by the aerosol mass spectrometer (AMS),
cavity ring down (CRD) and scanning mobility particle sizer (SMPS) systems.
At λ = 355 nm, the reacted aerosols demonstrate a substantial growth
in optical extinction cross section, as well as in mobility diameter under a
broad range of RH values (35–90%). The ratio of the product aerosol to
seed aerosol geometric cross section reached up to ~3.5, and the
optical extinction cross-section up to ~250. The reactions show a
trend of increasing physical and optical growth with decreasing seed aerosol
size, from 100 nm to 300 nm, as well as with decreasing RH values from 90%
to ~40%. Optically inactive aerosols, at the limit of the Mie range
(100 nm diameter) become optically active as they grow due to the reaction.
AMS analyses of the reaction of 300 nm AS at RH values of 50%, 75% and
90% show that the main products of the reaction are glyoxal oligomers,
formed by acetal formation in the presence of AS. In addition, imidazole
formation, which is a minor channel, is observed for all reactions, yielding
a product which absorbs at λ = 290 nm, with possible implications on
the radiative properties of the product aerosols. The ratio of absorbing
substances (C-N compounds, including imidazoles) increases with increasing
RH value. A core/shell model used for the investigation of the optical
properties of the reaction products of AS with gas phase glyoxal, shows that
the refractive index (RI) of the reaction products are n= 1.68(±0.10)+0.01(±0.02) at 50%
RH and n = 1.65(±0.06)+0.02(±0.01) at
75% RH at 355 nm. The observed increase in the ratio of the absorbing
substances is not indicated in the imaginary part of the products at RH
50% and 75%. A further increase in the ratio of absorbing substances
and a resulting increase in the imaginary part of the RI at higher RH values
is expected, and may become even more substantial after longer reaction
times, possibly in cloud or fog droplets. This study shows that the reaction
of abundant substances present in atmospheric aerosols, such as AS, and gas
phase glyoxal alters the aerosols' optical, physical and chemical properties
and may have implications on the radiative effect of these aerosols. |
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