Articles | Volume 3, issue 1
https://doi.org/10.5194/ar-3-231-2025
https://doi.org/10.5194/ar-3-231-2025
Opinion
 | 
05 May 2025
Opinion |  | 05 May 2025

Opinion: Influence of the mean free path of air on atmospheric particle growth

Runlong Cai and Markku Kulmala

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Cited articles

Allen, M. D. and Raabe, O. G.: Slip Correction Measurements of Spherical Solid Aerosol Particles in an Improved Millikan Apparatus, Aerosol Sci. Tech., 4, 269–286, https://doi.org/10.1080/02786828508959055, 1985. 
Cai, R.: Data for “Influence of the mean free path of air on atmospheric particle growth”, Zenodo [data set], https://doi.org/10.5281/zenodo.15294074, 2025. 
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Fuchs, N. A. and Sutugin, A. G.: Highly Disperse Aerosols, in: Topics in current aerosol research, edited by: Hidy, G. M. and Brock, J. R., Pergamon, New York, https://doi.org/10.1016/B978-0-08-016674-2.50006-6, 1971. 
Halonen, R., Zapadinsky, E., Kurtén, T., Vehkamäki, H., and Reischl, B.: Rate enhancement in collisions of sulfuric acid molecules due to long-range intermolecular forces, Atmos. Chem. Phys., 19, 13355–13366, https://doi.org/10.5194/acp-19-13355-2019, 2019.  
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Short summary
The concept of the mean free path is fundamentally important to aerosol studies. Recent studies suggest that the mean free path of air (λair) could have been significantly overestimated by a factor of ~2. Here we show that this potential overestimation does not directly affect collision-induced aerosol dynamics in atmospheric conditions without high excess latent heat, while a similar influence of the mean free path of vapor (λ) on aerosol dynamics has been accounted for in current studies.
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