Aerosol Dynamics on Inhalation at High Relative Humidity

呼吸道飞沫是COVID-19等疾病传播的原因。呼吸道飞沫的物理化学动力学尚不清楚。目前用于实验室研究的呼出气溶胶替代物的代表性仍存在争议。在这项研究中，使用了两种互补的仪器来测量呼吸替代溶液的微物理动力学和液滴ph的时间演变。结果表明，在环境相对湿度值范围内，病毒存活的不确定性取决于液滴的复杂相变行为，而这又取决于液滴的组成。呼出的气溶胶在一毫秒的时间尺度内经历pH值从中性到碱性的转变，这是导致病毒在气溶胶阶段失去传染性的原因。未来的实验将在更真实的二氧化碳调节环境下进行，更好地模拟飞沫所经历的气相条件，从而提高对空气传播疾病的认识。

Respiratory droplets are responsible for transmission of diseases such as COVID-19. The physicochemical dynamics of respiratory droplets are not well understood. The representativeness of surrogates for exhaled aerosol currently used for laboratory studies remains debated. In this study, two complementary instruments are used to measure the microphysical dynamics of respiratory surrogate solutions and the temporal evolution of droplet pH. Results show that within the range of ambient relative humidity values, uncertainty in viral survival is dependent upon the complex phase change behaviour of droplets, which in turn is dependent upon droplet composition. Exhaled aerosol experience a shift in pH, from neutral towards alkaline within a millisecond timescale, which is responsible for the infectivity loss of the virus in the aerosol phase. Future experiments will be carried out under a more realistic CO2-regulated environment to better simulate the gas phase conditions experienced by respiratory droplets thus improving the understanding of airborne disease transmission.