Some infections, including e.g. influenza and currently active COVID 19, may be transmitted via air during sneezing, coughing, and talking. This pathway occurs via diffusion and gravity-induced drift of single virions and respiratory droplets consisting primarily of water, including small fraction of nonvolatile matter, and containing virions. These processes are accompanied by water evaporation resulting in reduction of the droplet size. The manifold of information concerning these steps is presented in textbooks and articles not related to virology and the focus is there frequently on biologically irrelevant conditions and/or droplet sizes. In this brief review, we systematically describe the behavior of virions and virion-carrying droplets in air with emphasis on various regimes of diffusion, drift, and evaporation, and estimate the rates of all these steps under virologically relevant conditions. In addition, we discuss the kinetic aspects of the first steps of infection after attachment of virions or virion-carrying droplets to the epithelium, i.e., virion diffusion in the mucus and periciliary layers, penetration into the cells, and the early stage of replication. The presentation is oriented to virologists who are interested in the corresponding physics and to physicists who are interested in application of the physics to virology.

一些感染，包括流感和当前活跃的 COVID 19，可能会在打喷嚏、咳嗽和说话时通过空气传播。该途径通过单个病毒粒子和主要由水组成的呼吸液滴的扩散和重力诱导漂移而发生，包括少量非挥发性物质，并含有病毒粒子。这些过程伴随着水蒸发，导致液滴尺寸减小。有关这些步骤的大量信息出现在与病毒学无关的教科书和文章中，并且重点经常放在与生物学无关的条件和/或液滴大小上。在这篇简短的综述中，我们系统地描述了空气中病毒粒子和携带病毒粒子的液滴的行为，重点是各种扩散、漂移和蒸发机制，并估计在病毒学相关条件下所有这些步骤的速率。此外，我们还讨论了病毒粒子或携带病毒粒子的液滴附着到上皮细胞后感染第一步的动力学方面，即病毒粒子在粘液和纤毛周层中的扩散、渗透到细胞中以及复制的早期阶段。该演示文稿面向对相应物理学感兴趣的病毒学家和对物理学在病毒学中的应用感兴趣的物理学家。