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| Titel |
Iron-Catalyzed Activation of Chloride from Saline Media |
| VerfasserIn |
Julian Wittmer, Sergej Bleicher, Johannes Ofner, Cornelius Zetzsch |
| Konferenz |
EGU General Assembly 2015
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 17 (2015) |
| Datensatznummer |
250111216
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| Publikation (Nr.) |
 EGU/EGU2015-11306.pdf |
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| Zusammenfassung |
| Iron (Fe) occurs in highly saline media (e.g. sea salt aerosol, salt brines etc.). High salinity,
low pH, and organic constituents promote the dissolution of iron, forming photosensitive
complexes that are responsible for a gaseous Cl production when irradiated by sunlight
[1].
We studied the production of atomic Cl, Br and OH radicals from modeled salt pans [2]
and artificial sea-salt aerosols containing Fe(III) ions or pyrogenic Fe2O3particles (Sicotrans
Orange, BASF) at various compositions in a Teflon smog-chamber. The samples were
either spread on a Teflon sheet or they were nebulized from dilute brines (most
abundant particle diameter: ~0.4 μm, initial surface area: up to 3/
10-2 cm2cm-3) and
exposed to simulated sunlight at 60-90% relative humidity. The photochemical
formation of Cl, OH and Br (if possible) in the gas phase was quantified by the radical
clock method [3] resulting in time profiles of the radical-production rates and total
productions.
Simultaneous monitoring of the aerosol surface area enabled us to determine the initial
Cl production rate per cm2 aerosol surface. Whereas no significant Cl production
was detected employing a molar Cl-/Fe(III) ratio of 13, it increased to ~2.8/
1017
atoms cm-2s-1 (at a ratio of 101), ~4.1/
1017 atoms cm-2s-1(at a ratio of 53) and
~1.9/
1018 atoms cm-2s-1(at a ratio of 13). The presence of NO2 (~20 ppb) or
O3 (630 ppb) in the gas phase additionally increased the Fe(III)-induced chloride
activation to ~7/
1018 atoms cm-2s-1 and ~9/
1018 atoms cm-2s-1(at a Cl-/Fe(III)
ratio of 13), respectively. SO2 slightly restrained the Cl formation. Artificial sea
salt aerosols doped with Fe2O3 (Cl-/Fetot ~13) did not result in detectable Cl
concentrations. However, decreasing the pH below 2 favored the dissolution of
Fe and led to Cl production rates comparable to the Fe(III) experiments. These
observations are in accord with the speciation of the photolabile, aqueous Fe(III)
complexes obtained from an equilibrium model (PHREEQC) and supported by
SEM-EDX images (Scanning-Electron Microscope with an Energy-Dispersive X-ray
detector).
The aerosol experiments result in much higher effective Cl production rates with ~50%
of active Fe(III) in zero air compared to the salt pan experiments with a portion of
0.05-0.07% of active Fe(III), caused by the larger active surface area of the homogeneously
distributed aerosols.
[1] Lim et al. (2006) J. Photoch. Photobio. A: Chemistry, 183, 126-132 [2] Wittmer et al.
(2014) J. Phys. Chem. A, Article ASAP [3] Behnke et al. (1988) Atmos. Environ., 22,
1113-1120 |
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