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| Titel |
Aerosol-halogen interaction: Halogenation of secondary organic aerosols |
| VerfasserIn |
Johannes Ofner, Natalja Balzer, Sergej Bleicher, Joelle Buxmann, Hinrich Grothe, Heinz-Ulrich Krüger, Ulrich Platt, Philippe Schmitt-Kopplin, Cornelius Zetzsch |
| Konferenz |
EGU General Assembly 2011
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250056724
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| Zusammenfassung |
| The release of reactive halogen species from sea-salt aerosol contributes a new class of
reactants for heterogeneous reactions. These heterogeneous reactions have been overlooked
so far, although they may occur with internal and external mixtures of sea-salt aerosol and
organic aerosol and organic matter in soil. Such reactions might constitute sources of gaseous
organohalogen compounds or halogenated organic aerosol in the atmospheric boundary
layer.
To study the interaction of organic aerosols with released halogen species, secondary organic
aerosol (SOA) was produced from α-pinene, catechol and guaiacol using an aerosol
smog-chamber and characterized. Those aerosols were exposed to molecular halogens in the
presence of UV/VIS irradiation and to halogens, released from simulated natural
halogen sources like salt-pans, to study their behavior against those reactive trace
gases.
The entire organic aerosol and its physico-chemical transformation process were monitored
using various spectroscopic methods: Long-path-absorption- and Attenuated-Total-Reflectance
(ATR-)-FTIR were used to determine the changes of functional groups and structural
elements of the macromolecular aerosols. The optical properties in the UV/VIS range were
monitored using Diffuse-Reflectance-UV/VIS-Spectroscopy. The evolution and
change of the aerosol size distribution by the reaction with halogens was observed
using an electrostatic classifier coupled to a condensation nuclei counter. Finally,
Temperature-Programmed-Pyrolysis Mass-Spectroscopy (TPP-MS) and ultra-high resolution
Fourier-Transform-Mass-Spectroscopy (ICR-FT/MS) were used to determine the degrees of
halogenation and single halogenated molecules.
The heterogeneous reaction of reactive halogen species with those model aerosols leads to
different gaseous species like CO2, CO and small reactive molecules like phosgene. Methyl
groups (and possibly other C-H containing groups) on the aerosol particles are destroyed to
form HCl. Also carbon-oxygen bonds are affected by the reaction with these halogens, and a
significant formation of C-Br bonds could be verified in the particle phase. Overall, the
optical properties of the processed organic aerosols are significantly changed. Further,
the aerosol size distribution of the organic aerosols is strongly influenced by the
heterogeneous reaction. Studying the reaction of organic aerosols with molecular halogens at
different simulated environmental conditions allowed us to allocate changes of the
described physico-chemical parameters to specific reactive species and to interpret the
complex changes shown by the reaction with halogens released from the simulated
salt-pan.
The heterogeneous reaction of secondary organic aerosols with atmospheric halogen species
leads to changes of several physico-chemical features of the aerosol, influencing
their chemical composition, structural elements, their optical properties and size
distribution. Changes of the physical aerosol properties are carried out by the chemical
reaction, e.g. changing the ability to act as CCN or the contribution to radiative
forcing. |
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