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Titel |
Quantification of the volatility of secondary organic compounds in ultrafine particles during nucleation events |
VerfasserIn |
J. R. Pierce, I. Riipinen |
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 |
250059752
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Zusammenfassung |
Condensation of secondary organic compounds onto ultrafine aerosols is important for
growing these particles to sizes where they can act as cloud condensation nuclei. The organic
flux to ultrafine particles depends strongly on the volatility of the condensing compounds.
This paper presents quantitative estimates of the volatility of secondary organic aerosol
(SOA) in freshly nucleated particles. We examine 13 nucleation/growth events in two remote
continental locations, Hyytiälä, Finland and Egbert, ON, Canada. Two independent
methods are used to quantify the volatility of the growing nucleation mode: (1)
modelling of the growing nucleation mode to determine which volatilities allow
the model to reproduce observed growth, and (2) modelling of the evaporation of
heated aerosols in a Volatility Differential Mobility Particle Sizer to determine which
volatilities allow the model to reproduce the observed evaporation. We find that
the average saturation vapor concentration (C*) in the freshly nucleated particles
(once Dp > 3 nm) is likely less than 10-3-10-2 μg m-3 (this corresponds to
3-
106-3-
107 molecules cm-3 and a saturation vapor pressure of 10-8-10-7 Pa). This
maximum volatility depends somewhat on other uncertain factors that affect the
size-dependent condensation of secondary organic compounds such as the surface tension,
mass accommodation coefficient and the volatility of the pre-existing aerosols.
However, our tests suggest that under no reasonable assumptions can the SOA in the
ultrafine particles contain a majority of compounds with C* >10-2 μg m-3. We
demonstrate that the growth could be driven by either gas-phase or particle-phase
chemistry but cannot conclude which is responsible for the low-volatility SOA. |
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