By modelling the evaporation and settling of droplets emitted during respiratory releases and using previous measurements of droplet size distributions and SARS-CoV-2 viral load, estimates of the evolution of the liquid mass and the number of viral copies suspended were performed as a function of time from the release. The settling times of a droplet cloud and its suspended viral dose are significantly affected by the droplet composition. The aerosol (defined as droplets smaller than 5 μm) resulting from 30 s of continued speech has O(1 h) settling time and a viable viral dose an order-of-magnitude higher than in a short cough. The time-of-flight to reach 2 m is only a few seconds resulting in a viral dose above the minimum required for infection, implying that physical distancing in the absence of ventilation is not sufficient to provide safety for long exposure times. The suspended aerosol emitted by continuous speaking for 1 h in a poorly ventilated room gives 0.1–11% infection risk for initial viral loads of 108–1010 copies mll−l, respectively, decreasing to 0.03–3% for 10 air changes per hour by ventilation. The present results provide quantitative estimates useful for the development of physical distancing and ventilation controls.

中文翻译：

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呼吸道释放的喷雾和气溶胶的演变：深入了解病毒传播的理论估计


通过对呼吸释放过程中喷出的液滴的蒸发和沉降进行建模，并使用之前对液滴尺寸分布和 SARS-CoV-2 病毒载量的测量，对液体质量的演变和悬浮病毒拷贝数的估计作为以下函数进行：距离发布的时间。液滴云的沉降时间及其悬浮病毒剂量受液滴成分的显着影响。持续讲话 30 秒产生的气溶胶（定义为小于 5 μm 的液滴）的沉降时间为 O(1 小时)，且活病毒剂量比短时咳嗽高出一个数量级。到达 2 m 的飞行时间仅为几秒钟，导致病毒剂量高于感染所需的最低剂量，这意味着在缺乏通风的情况下保持物理距离不足以为长时间暴露提供安全保障。在通风不良的房间内连续说话 1 小时所释放的悬浮气溶胶，对于初始病毒载量为 108-1010 拷贝 mll−l 的感染风险分别为 0.1-11%，每小时换气 10 次，感染风险降低至 0.03-3%通风。目前的结果提供了有助于制定物理距离和通风控制的定量估计。