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| Titel |
Compilation and evaluation of gas phase diffusion coefficients of reactive trace gases in the atmosphere: Volume 2. Diffusivities of organic compounds, pressure-normalised mean free paths, and average Knudsen numbers for gas uptake calculations |
| VerfasserIn |
M. J. Tang, M. Shiraiwa, U. Pöschl, R. A. Cox, M. Kalberer |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1680-7316
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 15, no. 10 ; Nr. 15, no. 10 (2015-05-21), S.5585-5598 |
| Datensatznummer |
250119743
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| Publikation (Nr.) |
 copernicus.org/acp-15-5585-2015.pdf |
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| Zusammenfassung |
| Diffusion of organic vapours to the surface of aerosol or cloud particles is
an important step for the formation and transformation of atmospheric
particles. So far, however, a database of gas phase diffusion coefficients
for organic compounds of atmospheric interest has not been available. In
this work we have compiled and evaluated gas phase diffusivities
(pressure-independent diffusion coefficients) of organic compounds
reported by previous experimental studies, and we compare the measurement
data to estimates obtained with Fuller's semi-empirical method. The
difference between measured and estimated diffusivities are mostly < 10%. With regard to gas-particle interactions, different gas molecules,
including both organic and inorganic compounds, exhibit similar Knudsen
numbers (Kn) although their gas phase diffusivities may vary over a wide
range. This is because different trace gas molecules have similar mean free
paths in air at a given pressure. Thus, we introduce the pressure-normalised
mean free path, λP ≈ 100 nm atm, as a near-constant
generic parameter that can be used for approximate calculation of Knudsen
numbers as a simple function of gas pressure and particle diameter to
characterise the influence of gas phase diffusion on the uptake of gases by
aerosol or cloud particles. We use a kinetic multilayer model of
gas-particle interaction to illustrate the effects of gas phase diffusion on
the condensation of organic compounds with different volatilities. The
results show that gas phase diffusion can play a major role in determining
the growth of secondary organic aerosol particles by condensation of
low-volatility organic vapours. |
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