| 26 Feb 2025
Opinion: Influence of mean free path of air on atmospheric particle growth
Abstract. Recent studies by Tsalikis et al. (2023, 2024) predicted that the mean free path of air (λair) could be significantly smaller than widely used values by a factor of ~2. Given the fundamental importance of λair, it has been a question that whether an overestimation of λair would have profound influences on a number of aerosol processes. Here we assume that the newly proposed value of λair is accurate and examine its influences on our understanding of atmospheric aerosols. We show that for collisions-induced aerosol dynamics such as the condensation growth of atmospheric particles, the collision rate and hence the growth rate are determined by an effective mean free path for vapor and particle collision rather than λair. Similar to the cause of a smaller λair, the overlooked force field in hard-sphere models may enhance vapor-particle collisions; however, this enhancement has been accounted for in previous studies. As a result, we find that the smaller λair does not directly influence particle collisions, i.e., it does not challenge the previous understandings on particle growth in the lowertroposhpere. Other potential influences on growth involving a high excess latent heat and the uncertainties in the sub-5 nm size range are also addressed.
Competing interests: At least one of the (co-)authors is a member of the editorial board of Aerosol Research.
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