The airborne dynamics of respiratory droplets, and the transmission routes of pathogens embedded within them, are governed primarily by the diameter of the particles. These particles are composed of the fluid which lines the respiratory tract, and is primarily mucins and salts, which will interact with the atmosphere and evaporate to reach an equilibrium diameter. Measuring organic volume fraction (OVF) of cough aerosol has proved challenging due to large variability and low material volume produced after coughing. Here, the diametric hygroscopic growth factors (GF) of the cough aerosol produced by healthy participants were measured in situ using a rotating aerosol suspension chamber and a humidification tandem differential mobility analyser. Using hygroscopicity models, it was estimated that the average OVF in the evaporated cough aerosol was 0.88 ± 0.07 and the average GF at 90% relative humidity (RH) was 1.31 ± 0.03. To reach equilibrium in dry air the droplets will reduce in diameter by a factor of approximately 2.8 with an evaporation factor of 0.36 ± 0.05. Hysteresis was observed in cough aerosol at RH = ∼35% and RH = ∼65% for efflorescence and deliquescence, respectively, and may depend on the OVF. The same behaviour and GF were observed in nebulized bovine bronchoalveolar lavage fluid.

呼吸道飞沫在空气中的动态以及其中嵌入的病原体的传播途径主要取决于颗粒的直径。这些颗粒由呼吸道内的液体组成，主要是粘蛋白和盐，它们会与大气相互作用并蒸发以达到平衡直径。由于咳嗽后产生的物质体积大且变异性大，测量咳嗽气溶胶的有机体积分数 (OVF) 已被证明具有挑战性。在这里，使用旋转气溶胶悬浮室和加湿串联微分迁移率分析仪原位测量健康参与者产生的咳嗽气溶胶的直径吸湿生长因子（GF） 。使用吸湿性模型，估计蒸发的咳嗽气溶胶中的平均 OVF 为 0.88 ± 0.07，90% 相对湿度 (RH) 下的平均 GF 为 1.31 ± 0.03。为了在干燥空气中达到平衡，液滴的直径将减小约 2.8 倍，蒸发系数为 0.36 ± 0.05。在咳嗽气雾剂中观察到风化和潮解的滞后现象分别为 RH = ∼35% 和 RH = ∼65%，并且可能取决于 OVF。在雾化牛支气管肺泡灌洗液中观察到相同的行为和 GF。