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| Titel |
Artifacts in measuring aerosol uptake kinetics: the roles of time, concentration and adsorption |
| VerfasserIn |
L. H. Renbaum, G. D. Smith |
| 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. 14 ; Nr. 11, no. 14 (2011-07-18), S.6881-6893 |
| Datensatznummer |
250009921
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| Publikation (Nr.) |
 copernicus.org/acp-11-6881-2011.pdf |
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| Zusammenfassung |
| In laboratory studies of organic aerosol particles reacting with gas-phase
oxidants, high concentrations of radicals are often used to study on the
timescale of seconds reactions which may be occurring over days or weeks in
the troposphere. Implicit in this approach is the assumption that radical
concentration and time are interchangeable parameters, though this has not
been established. Here, the kinetics of OH- and Cl-initiated oxidation
reactions of model single-component liquid (squalane) and supercooled
(brassidic acid and 2-octyldodecanoic acid) organic aerosols are studied by
varying separately the radical concentration and the reaction time. Two
separate flow tubes with residence times of 2 and 66 s are used, and [OH] and
[Cl] are varied by adjusting either the laser photolysis fluence or the
radical precursor concentration ([O3] or [Cl2], respectively) used
to generate the radicals. It is found that the rates measured by varying the
radical concentration and the reaction time are equal only if the precursor
concentrations are the same in the two approaches. Further, the rates depend
on the concentrations of the precursor species with a Langmuir-type
functional form suggesting that O3 and Cl2 saturate the surface of
the liquid particles. It is believed that the presence of O3 inhibits
the rate of OH reaction, perhaps by reacting with OH radicals or by O3
or intermediate species blocking surface sites, while Cl2 enhances the
rate of Cl reaction by participating in a radical chain mechanism. These
results have important implications for laboratory experiments in which high
concentrations of gas-phase oxidants are used to study atmospheric reactions
over short timescales and may explain the variability in recent measurements
of the reactive uptake of OH on squalane particles in reactor systems used in
this and other laboratories. |
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