Respiratory aerosols and droplets in the transmission of infectious diseases

The pandemic of coronavirus disease 2019 has led to a renewed focus on the physicochemical properties of the droplets and aerosol particles that are exhaled during breathing, speaking, singing, coughing, and sneezing. In this article, the properties of respiratory particles, including their number concentrations and size distributions, as well as their formation mechanisms at different sites in the respiratory system, are reviewed. The data in the literature are synthesized via a parametrization of the particle size distribution data using log-normal modes related to the different origin sites.