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| Titel |
Kinetic smog-chamber studies on halogen activation from a simulated salt pan, using dry and wet NaCl/NaBr surfaces |
| VerfasserIn |
Sergej Bleicher, Natalja Balzer, Cornelius Zetzsch, Joelle Buxmann, Ulrich Platt |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250036730
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| Zusammenfassung |
| Field experiments and laboratory studies have shown that atomic Br and Cl are released from
sea-salt aerosol and saline soils. This halogen release is based on the uptake of
gaseous HOX by aqueous, acidified salt surfaces. Br and Cl play an important role in
atmospheric ozone depletion and the destruction of hydrocarbons. Furthermore, Secondary
Organic Aerosol (SOA) and HUmic LIke Substances (HULIS) may take part in
these reaction cycles by halogenation and production of volatile organic halogen
compounds.
Aerosol smog-chamber facilities (coolable to -25°C) enable us to simulate the halogen
release mechanism under arctic tropospheric conditions. Mechanistic and kinetic studies are
carried out to investigate the influence of SOA and HULIS on halogen cycles and to
determine halogenated gaseous and solid organic products.
The present laboratory measurements study halogen activation from salt surfaces, which are
similar to typical salt pan environments. In these experiments we placed different
artificial salt mixtures with NaCl/NaBr ratios up to 300:1 on a Teflon pan located in a
Teflon chamber with a volume of 3.5 m3. Under clean air conditions we inject ozone
and a mixture of non-methane hydrocarbons with well-known reactivities against
OH and Cl and irradiated the chamber with a solar simulator. Beside the usual
observing instruments like an ozone monitor and a gas chromatograph we used
Differential Optical Absorption Spectroscopy (DOAS) in a White cell with a light
path up to 320 m to observe various gas-phase species including BrO radicals.
A dry air / dry salt pan environment showed no ozone depletion and no halogen
activation. At relative humidity above 50%, a rapid ozone depletion (4.7 h half-life)
was observed, which is much faster than for pure NaCl under the same conditions
(77 h). Furthermore, the mixed salt was acidified with H2SO4 to a pH value of
4.3, no difference in ozone depletion and halogen activation was observed at this
point.
The DOAS measurements are the first simultaneous observations of ozone depletion and BrO
radicals in the laboratory. Using the radical clock technique we measured concentration time
profiles of OH and Cl with integrated values up to 8 -
1010 molec/cm3 for OH and up to
5 -
108 molec/cm3 for Cl.
With such halogen release out of a salt pan we can study the halogenation of SOA particles in
environmentally relevant conditions.
Acknowledgement
We would like to thank the DFG for funding the HALOPROC project (research unit
963). |
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