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| Titel |
Formation of halogen-induced secondary organic aerosol (XOA) |
| VerfasserIn |
J. Ofner, K. Kamilli, A. Held, C. Zetzsch |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250064432
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| Zusammenfassung |
| Reactive halogen species (RHS) are released to the atmosphere from sources like
photo-activated sea-salt aerosol and salt lakes. RHS seem to interact with SOA precursors
similarly to common atmospheric oxidizing gases like OH radicals and ozone. Aerosol
formation from reaction of RHS with typical SOA precursors was studied by Cai
et al. (2006, 2008) using an aerosol mass spectrometer. No data is available on
bromine-induced aerosol formation from organic precursors. The potential interaction of
RHS with secondary organic aerosol (SOA) has recently been studied by Ofner et al.
(2011).
A 700 Liter aerosol smog-chamber was used to generate halogen-induced secondary
organic aerosol (XOA). The chosen precursor concentration of 10 ppb for the biogenic
precursors and 2 ppb for molecular chlorine and 10 ppb for molecular bromine are
close to natural conditions. XOA formation in the smog chamber was initiated
using a solar simulator. To follow the aerosol formation process, the aerosol size
distribution, the ozone and NOx mixing ratios and the decay of the aerosol precursor
were measured and compared to the calculated photolysis of the molecular halogen
species.
Even very low precursor and RHS concentrations form XOA particles with a mode at
about 20 nm and a number concentration up to 104 particles cm-3. While the XOA
formation from chlorine is very rapid, the interaction of bromine with the organic
precursors is about five times slower. The present study compares the XOA formation
potential of photolyzed chlorine and bromine with several typical SOA precursors
and relates the formation to the calculated photolysis of the RHS. The formation
of XOA at atmospherically relevant concentrations in an aerosol smog-chamber
suggests natural XOA formation at marine sites, where organic precursor emissions
(biogenic or anthropogenic) are close to RHS emitting sea-salt aerosol or salt lakes. The
formation of XOA then interacts with the halogen-release cycles by slowing them
down.
References:
Cai, X., and Griffin, R. J.: Secondary aerosol formation from the oxidation of biogenic
hydrocarbons by chlorine atoms, J. Geophys. Res., 111, D14206/14201-D14206/14214,
2006.
Cai, X., Ziemba, L. D., and Griffin, R. J.: Secondary aerosol formation from the oxidation
of toluene by chlorine atoms, Atmos. Environ., 42, 7348-7359, 2008.
Ofner, J., Balzer, N., Buxmann, J., Grothe, H., Schmitt-Kopplin, Ph., Platt, U., and
Zetzsch, C., Halogenation processes of secondary organic aerosol and implications on
halogen release mechanisms, ACPD, 2011, submitted. |
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