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| Titel |
Glyoxal processing by aerosol multiphase chemistry: towards a kinetic modeling framework of secondary organic aerosol formation in aqueous particles |
| VerfasserIn |
B. Ervens, R. Volkamer |
| 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 ; 10, no. 17 ; Nr. 10, no. 17 (2010-09-02), S.8219-8244 |
| Datensatznummer |
250008746
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| Publikation (Nr.) |
 copernicus.org/acp-10-8219-2010.pdf |
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| Zusammenfassung |
This study presents a modeling framework based on laboratory data to
describe the kinetics of glyoxal reactions that form secondary organic
aerosol (SOA) in aqueous aerosol particles. Recent laboratory results on
glyoxal reactions are reviewed and a consistent set of empirical reaction
rate constants is derived that captures the kinetics of glyoxal hydration
and subsequent reversible and irreversible reactions in aqueous inorganic
and water-soluble organic aerosol seeds. Products of these processes include
(a) oligomers, (b) nitrogen-containing products, (c) photochemical oxidation
products with high molecular weight. These additional aqueous phase
processes enhance the SOA formation rate in particles and yield two to three
orders of magnitude more SOA than predicted based on reaction schemes for
dilute aqueous phase (cloud) chemistry for the same conditions (liquid water
content, particle size).
The application of the new module including detailed chemical processes in a
box model demonstrates that both the time scale to reach aqueous phase
equilibria and the choice of rate constants of irreversible reactions have a
pronounced effect on the predicted atmospheric relevance of SOA formation
from glyoxal. During day time, a photochemical (most likely
radical-initiated) process is the major SOA formation pathway forming
∼5 μg m−3 SOA over 12 h (assuming a constant glyoxal mixing
ratio of 300 ppt). During night time, reactions of nitrogen-containing
compounds (ammonium, amines, amino acids) contribute most to the predicted
SOA mass; however, the absolute predicted SOA masses are reduced by an order
of magnitude as compared to day time production. The contribution of the
ammonium reaction significantly increases in moderately acidic or neutral
particles (5 < pH < 7).
Glyoxal uptake into ammonium sulfate seed under dark conditions can be
represented with a single reaction parameter keffupt that does not
depend on aerosol loading or water content, which indicates a possibly
catalytic role of aerosol water in SOA formation. However, the reversible
nature of uptake under dark conditions is not captured by keffupt, and
can be parameterized by an effective Henry's law constant including an
equilibrium constant Kolig = 1000 (in ammonium sulfate solution). Such
reversible glyoxal oligomerization contributes <1% to total predicted
SOA masses at any time.
Sensitivity tests reveal five parameters that strongly affect the predicted
SOA mass from glyoxal: (1) time scales to reach equilibrium states (as
opposed to assuming instantaneous equilibrium), (2) particle pH, (3)
chemical composition of the bulk aerosol, (4) particle surface composition,
and (5) particle liquid water content that is mostly determined by the
amount and hygroscopicity of aerosol mass and to a lesser extent by the
ambient relative humidity.
Glyoxal serves as an example molecule, and the conclusions about SOA
formation in aqueous particles can serve for comparative studies of other
molecules that form SOA as the result of multiphase chemical processing in
aerosol water. This SOA source is currently underrepresented in atmospheric
models; if included it is likely to bring SOA predictions (mass and O/C
ratio) into better agreement with field observations. |
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