Opinion: Influence of the mean free path of air on atmospheric particle growth
<p>Recent studies by Tsalikis et al. (2023, 2024) predicted that the mean free path of air (<span class="inline-formula"><i>λ</i><sub>air</sub></span>) could be significantly smaller than widely used values by a factor of <span class="inlin...
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Copernicus Publications
2025-05-01
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| Series: | Aerosol Research |
| Online Access: | https://ar.copernicus.org/articles/3/231/2025/ar-3-231-2025.pdf |
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| author | R. Cai M. Kulmala |
| author_facet | R. Cai M. Kulmala |
| author_sort | R. Cai |
| collection | DOAJ |
| description | <p>Recent studies by Tsalikis et al. (2023, 2024) predicted that the mean free path of air (<span class="inline-formula"><i>λ</i><sub>air</sub></span>) could be significantly smaller than widely used values by a factor of <span class="inline-formula">∼</span> 2. Given the fundamental importance of <span class="inline-formula"><i>λ</i><sub>air</sub></span>, the question of whether an overestimation of <span class="inline-formula"><i>λ</i><sub>air</sub></span> would have profound influence on a number of aerosol processes must be answered. Here we assume that the newly proposed value of <span class="inline-formula"><i>λ</i><sub>air</sub></span> is accurate and examine its influences on our understanding of atmospheric aerosols. We show that for collision-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 by <span class="inline-formula"><i>λ</i><sub>air</sub></span>. Similar to the cause of a smaller <span class="inline-formula"><i>λ</i><sub>air</sub></span>, the overlooked force field in pure elastic models may enhance vapor–particle collisions; however, this enhancement has been accounted for in previous studies. As a result, we find that the smaller <span class="inline-formula"><i>λ</i><sub>air</sub></span> does not substantially influence particle collisions; i.e., it does not challenge our previous understanding of particle growth in the lower troposphere. Other potential influences on growth involving high excess latent heat and the uncertainties in the sub-5 nm size range are also addressed.</p> |
| format | Article |
| id | doaj-art-b9d61a0d874f4c3bb7d23ee950493f69 |
| institution | DOAJ |
| issn | 2940-3391 |
| language | English |
| publishDate | 2025-05-01 |
| publisher | Copernicus Publications |
| record_format | Article |
| series | Aerosol Research |
| spelling | doaj-art-b9d61a0d874f4c3bb7d23ee950493f692025-08-20T03:10:58ZengCopernicus PublicationsAerosol Research2940-33912025-05-01323123510.5194/ar-3-231-2025Opinion: Influence of the mean free path of air on atmospheric particle growthR. Cai0M. Kulmala1Shanghai Key Laboratory of Atmospheric Particle Pollution and Prevention (LAP), Department of Environmental Science & Engineering, Fudan University, Shanghai 200438, ChinaInstitute for Atmospheric and Earth System Research/Physics, Faculty of Science, University of Helsinki, Helsinki 00014, Finland<p>Recent studies by Tsalikis et al. (2023, 2024) predicted that the mean free path of air (<span class="inline-formula"><i>λ</i><sub>air</sub></span>) could be significantly smaller than widely used values by a factor of <span class="inline-formula">∼</span> 2. Given the fundamental importance of <span class="inline-formula"><i>λ</i><sub>air</sub></span>, the question of whether an overestimation of <span class="inline-formula"><i>λ</i><sub>air</sub></span> would have profound influence on a number of aerosol processes must be answered. Here we assume that the newly proposed value of <span class="inline-formula"><i>λ</i><sub>air</sub></span> is accurate and examine its influences on our understanding of atmospheric aerosols. We show that for collision-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 by <span class="inline-formula"><i>λ</i><sub>air</sub></span>. Similar to the cause of a smaller <span class="inline-formula"><i>λ</i><sub>air</sub></span>, the overlooked force field in pure elastic models may enhance vapor–particle collisions; however, this enhancement has been accounted for in previous studies. As a result, we find that the smaller <span class="inline-formula"><i>λ</i><sub>air</sub></span> does not substantially influence particle collisions; i.e., it does not challenge our previous understanding of particle growth in the lower troposphere. Other potential influences on growth involving high excess latent heat and the uncertainties in the sub-5 nm size range are also addressed.</p>https://ar.copernicus.org/articles/3/231/2025/ar-3-231-2025.pdf |
| spellingShingle | R. Cai M. Kulmala Opinion: Influence of the mean free path of air on atmospheric particle growth Aerosol Research |
| title | Opinion: Influence of the mean free path of air on atmospheric particle growth |
| title_full | Opinion: Influence of the mean free path of air on atmospheric particle growth |
| title_fullStr | Opinion: Influence of the mean free path of air on atmospheric particle growth |
| title_full_unstemmed | Opinion: Influence of the mean free path of air on atmospheric particle growth |
| title_short | Opinion: Influence of the mean free path of air on atmospheric particle growth |
| title_sort | opinion influence of the mean free path of air on atmospheric particle growth |
| url | https://ar.copernicus.org/articles/3/231/2025/ar-3-231-2025.pdf |
| work_keys_str_mv | AT rcai opinioninfluenceofthemeanfreepathofaironatmosphericparticlegrowth AT mkulmala opinioninfluenceofthemeanfreepathofaironatmosphericparticlegrowth |