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| Titel |
The effect of fatty acid surfactants on the uptake of nitric acid to deliquesced NaCl aerosol |
| VerfasserIn |
K. Stemmler, A. Vlasenko, C. Guimbaud, M. Ammann |
| 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 ; 8, no. 17 ; Nr. 8, no. 17 (2008-09-02), S.5127-5141 |
| Datensatznummer |
250006355
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| Publikation (Nr.) |
 copernicus.org/acp-8-5127-2008.pdf |
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| Zusammenfassung |
| Surface active organic compounds have been observed in marine boundary layer
aerosol. Here, we investigate the effect such surfactants have on the uptake
of nitric acid (HNO3), an important removal reaction of nitrogen oxides
in the marine boundary layer. The uptake of gaseous HNO3 on deliquesced
NaCl aerosol was measured in a flow reactor using HNO3 labelled with
the short-lived radioactive isotope 13N. The uptake coefficient γ on pure
deliquesced NaCl aerosol was γ=0.5±0.2 at 60% relative humidity and 30 ppb HNO3(g). The uptake
coefficient was reduced by a factor of 5–50 when the aerosol was coated with
saturated linear fatty acids with carbon chain lengths of 18 and 15 atoms in
monolayer quantities. In contrast, neither shorter saturated linear fatty
acids with 12 and 9 carbon atoms, nor coatings with the unsaturated oleic
acid (C18, cis-double bond) had a detectable effect on the rate of HNO3
uptake. It is concluded that it is the structure of the monolayers formed,
which determines their resistance towards HNO3 uptake. Fatty acids (C18
and C15), which form a highly ordered film in the so-called liquid condensed
state, represent a significant barrier towards HNO3 uptake, while
monolayers of shorter-chain fatty acids (C9, C12) and of the unsaturated
oleic acid form a less ordered film in the liquid expanded state and do not
hinder the uptake. Similarly, high contents of humic acids in the aerosol, a
structurally inhomogeneous, quite water soluble mixture of oxidised high
molecular weight organic compounds did not affect HNO3 uptake. As
surfactant films on naturally occurring aerosol are expected to be less
structured due to their chemical inhomogeneity, it is likely that their
inhibitory effect on HNO3 uptake is smaller than that observed here for
the C15 and C18 fatty acid monolayers. |
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