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mean free path, λ

The average distance a molecule travels between collisions. For a molecule, λ = ( 2 π n d m 2 ) −1, where n is the number of molecules per unit volume and d m is their mean diameter. For O2 at one atmosphere and 25 °C, this distance is only 9.7 × 10 −6 cm; at 10 −6 atmospheres and 25 °C it is 9.7 cm. For an aerosol particle, the mean free path, λ B in the Stokes region (see Stokes law) is given by: λ B = 3 k T m m B where m is the mass of the particle, k is the Boltzmann constant (1.381 × 10 −23 J K −1), T is the temperature (K) and B is the mobility.
Source:
PAC, 1990, 62, 2167 (Glossary of atmospheric chemistry terms (Recommendations 1990)) on page 2201
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IUPAC. Compendium of Chemical Terminology, 2nd ed. (the "Gold Book"). Compiled by A. D. McNaught and A. Wilkinson. Blackwell Scientific Publications, Oxford (1997). XML on-line corrected version: http://goldbook.iupac.org (2006-) created by M. Nic, J. Jirat, B. Kosata; updates compiled by A. Jenkins. ISBN 0-9678550-9-8. doi:10.1351/goldbook.
Last update: 2014-02-24; version: 2.3.3.
DOI of this term: doi:10.1351/goldbook.M03778.
Original PDF version: http://www.iupac.org/goldbook/M03778.pdf. The PDF version is out of date and is provided for reference purposes only. For some entries, the PDF version may be unavailable.
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