Journal cover Journal topic
Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
Journal topic

Journal metrics

IF value: 5.414
IF 5-year value: 5.958
IF 5-year
CiteScore value: 9.7
SNIP value: 1.517
IPP value: 5.61
SJR value: 2.601
Scimago H <br class='widget-line-break'>index value: 191
Scimago H
h5-index value: 89
Volume 15, issue 10
Atmos. Chem. Phys., 15, 5585–5598, 2015
© Author(s) 2015. This work is distributed under
the Creative Commons Attribution 3.0 License.
Atmos. Chem. Phys., 15, 5585–5598, 2015
© Author(s) 2015. This work is distributed under
the Creative Commons Attribution 3.0 License.

Review article 21 May 2015

Review article | 21 May 2015

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

M. J. Tang1, M. Shiraiwa2, U. Pöschl2, R. A. Cox1, and M. Kalberer1 M. J. Tang et al.
  • 1Department of Chemistry, University of Cambridge, Cambridge CB2 1EW, UK
  • 2Multiphase Chemistry Department, Max Planck Institute for Chemistry, 55128, Mainz, Germany

Abstract. 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.

Publications Copernicus
Final-revised paper