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| Titel |
Ozone uptake and formation of reactive oxygen intermediates on glassy, semi-solid and liquid organic matter |
| VerfasserIn |
Thomas Berkemeier, Sarah S. Steimer, Ulrich K. Krieger, Thomas Peter, Ulrich Pöschl, Markus Ammann, Manabu Shiraiwa |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250135731
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| Publikation (Nr.) |
 EGU/EGU2016-16630.pdf |
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| Zusammenfassung |
| Heterogeneous and multiphase reactions of ozone are important pathways for chemical
ageing of atmospheric organic aerosols (Abbatt, Lee and Thornton, 2012). The
effects of particle phase state on the reaction kinetics are still not fully elucidated and
cannot be described by classical models assuming a homogeneous condensed phase
(Berkemeier et al., 2013). We apply a kinetic multi-layer model, explicitly resolving gas
adsorption, condensed phase diffusion and condensed phase chemistry (Shiraiwa et al.,
2010), to systematic measurements of ozone uptake onto proxies for secondary
organic aerosols (SOA). Our findings show how moisture-induced phase changes
affect the gas uptake and chemical transformation of organic matter through change
in the physicochemical properties of the substrate: the diffusion coefficients are
found to be low under dry conditions, but increase by several orders of magnitude
toward higher relative humidity (RH). The solubility of ozone in the dry organic
matrix is found to be one order of magnitude higher than in the dilute aqueous
solution.
The model simulations reveal that at high RH, ozone uptake is mainly controlled by
reaction throughout the particle bulk, whereas at low RH, bulk diffusion is retarded
severely and reaction at the surface becomes the dominant pathway, with ozone uptake
being limited by replenishment of unreacted organic molecules from the bulk phase.
The experimental results can only be reconciled including a pathway for ozone
self-reaction, which becomes especially important under dry and polluted conditions.
Ozone self-reaction can be interpreted as formation and recombination of long-lived
reactive oxygen intermediates at the aerosol surface, which could also explain several
kinetic parameters and has implications for the health effects of organic aerosol
particles.
This study hence outlines how kinetic modelling can be used to gain mechanistic insight into
the coupling of mass transport, phase changes, and chemical reactions in complex multiphase
reaction systems.
References
J. P. D. Abbatt, A. K. Y. Lee and J. A. Thornton, Chem. Soc. Rev., 2012, 41,
6555-6581.
T. Berkemeier et al., Atmos. Chem. Phys., 2013, 13, 6663-6686.
M. Shiraiwa, C. Pfrang and U. Pöschl, Atmos. Chem. Phys., 2010, 10, 3673-3691. |
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