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| Titel |
Competition of homogeneous and heterogeneous ice nucleation on secondary organic aerosol particles: The role of particle phase state |
| VerfasserIn |
Thomas Berkemeier, Manabu Shiraiwa, Ulrich Pöschl, Thomas Koop |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250098261
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| Publikation (Nr.) |
 EGU/EGU2014-13925.pdf |
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| Zusammenfassung |
| Recently, secondary organic aerosol (SOA) particles have been found to exhibit a highly
viscous, amorphous state under atmospherically relevant conditions (Virtanen et al., 2010).
Besides retardation of chemical reactions (Shiraiwa et al., 2011) and incomplete
gas-to-particle partitioning of semi-volatile constituents (Vaden et al., 2011), these particles
were found to suppress homogeneous ice nucleation (Murray et al., 2008), which normally
takes place when a liquid particle reaches its respective homogeneous nucleation limit (Koop
et al., 2000). In turn, glassy SOA particles may act themselves as heterogeneous ice
nuclei as recent studies suggest (e.g. Murray et al., 2010, Wang et al., 2012). The
predominant nucleation pathway for SOA particles is thus controlled by particle phase
state.
The phase state of SOA particles depends on several factors such as composition,
temperature and relative humidity. In atmospheric updrafts, inducing a change in temperature
and relative humidity, moisture- and temperature-induced phase transitions can occur (e.g.
Shiraiwa et al., 2011). In fast updrafts, these particles may also deviate from humidification
equilibrium, i.e. the agreement between ambient relative humidity and water activity inside
the particle may not be established at any point in time. The extent of this temporal delay is
governed by the updraft velocity, the particle size and the diffusivity of water inside the
glassy organic particle matrix.
Here we show how the delayed deliquescence of SOA particles can be quantified for SOA
from a variety of precursors. A kinetic flux model (Shiraiwa et al., 2012) is applied
and the predominant ice nucleation pathway is inferred from particle phase state
at the respective homogeneous and heterogeneous nucleation limits. To estimate
diffusivities inside the organic particle matrix for the relevant range of temperature and
humidity, we developed a novel method that relies on glass transition and hygroscopic
growth data that are more easily available. The model simulations suggest upper
temperature boundaries, below which heterogeneous ice nucleation of glassy aerosols may
occur, depending on updraft velocities and particle size. We also show that the
predominant ice nucleation pathway depends on precursor material and oxidation
state.
References
Koop, T. et al. (2000) Nature 406, 611.
Murray, B. J. (2008) Atmos. Chem. Phys. 8, 5423.
Murray, B. J. et al. (2010) Nature Geosci. 3, 233.
Shiraiwa, M. et al. (2011) Proc. Natl. Acad. Sci. 108, 11003.
Shiraiwa, M. et al. (2012) Atmos. Chem. Phys. 12, 2777.
Virtanen, A. et al. (2010) Nature 467, 824.
Vaden, T. D. et al. (2011) Proc. Natl. Acad. Sci., 108, 2190.
Wang, B. et al. (2012) J. Geophys. Res., 117, D16209. |
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