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| Titel |
Smog Chamber Investigation on the Iron-Catalyzed Activation of Chloride from Modeled Saltpans |
| VerfasserIn |
Julian Wittmer, Sergej Bleicher, Franz Dietrich Oeste, Cornelius Zetzsch |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250086987
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| Publikation (Nr.) |
 EGU/EGU2014-941.pdf |
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| Zusammenfassung |
| Halogen activation on sea spray aerosols and other halide surfaces and thus the formation of
reactive halogen species (RHS), influencing trace and greenhouse gases, has become an
important topic of research in recent years. In this context the chloride and bromide
activation, in particular the formation of RHS by photochemically induced halogen release
from (sea) salt surface and reactions with ozone (O3) and nitrogen oxides (NOx), came into
focus [1,2].
Our studies concentrate on the quantification of atomic chlorine (Cl), bromine (Br) and
hydroxyl (OH) radicals in the gas phase above lab-models of salt pans, enriched in iron(III)
chloride (FeCl3), that are exposed to simulated sunlight in a smog chamber. The applied
radical clock method [3] results in time profiles and source strengths for Cl, Br and OH,
which are combined with the various compositions of humidified salts. In particular, the
influence of bromine, sulfate, oxalate, and catechol on the FeCl3 enriched salt is investigated.
Comparable investigations only exist for the aqueous phase chemistry of FeCl3 (e.g.
[4]).
Driven by the photolytic reduction from Fe(III) to Fe(II), an enormous amount of chlorine
atoms (>107 cm-3) could be detected for sodium chloride (NaCl) salt pans with low
addition of FeCl3 (0.5 - 2 wt%), even in an O3 and NOx free environment. The Cl2
source strength reaches a maximum of 8x1011 Cl2 molecules per cm3 within the
first hour of the experiment, corresponding to a Cl2 mixing ratio of 30 ppbv at
standard pressure.These concentrations exceeded the release above pure NaCl
samples by a factor of 1000. A crucial factor for the Cl2 release is the pH and thus the
formation of iron(III) complexes on the salt crystals that differ in their sensitivity for
photolysis. Whereas the presence of sodium bromide normally strengthens the chlorine
release, a suppression accompanied by strong bromine activation (>1010 cm-3)
could be observed for iron enriched samples. Furthermore, the addition of sodium
sulfate, sodium oxalate and catechol to NaCl/FeCl3 samples restrains the activation
of chloride. The observations are in accord with a simple equilibrium model that
shows the pH-dependence of the formed species in the quasi-liquid layer on the
salt.
[1] Vogt et al. (1996) Nature, 383, 327-330 [2] Buxmann et al. (2012) Int. J. Chem.
Kinetics, 44, 312-326 [3] Behnke et al. (1988) Atmos. Environ., 22, 1113-1120 [4] Lim et al.
(2006) Journal of Photochemistry and Photobiology A: Chemistry, 183, 126-132 |
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