There is growing evidence that aerosols are an important route of transmission of COVID-19. The virus that causes the disease, SARS-CoV-2, has been found directly in the exhaled breath of patients and in the air of hospital rooms, and it can survive in aerosols for many hours. Certain superspreading events are best explained by aerosols. Transmission of infectious disease by aerosols is a highly interdisciplinary topic that draws upon epidemiology, virology, and aerosol science. Breathing, talking, coughing, and sneezing release respiratory droplets spanning a wide range of sizes. These may contain virus if a person is infected. Physically, virus-laden droplets are subject to the same transport and removal mechanisms as are airborne particles, so we can apply fundamental principles about particle behavior to understand the dynamics of virus in the air. Evaporation of respiratory droplets leads to shrinkage and changes in chemical composition, such as altered pH, increased salt and protein concentrations, crystallization, or phase separation, that may affect virus viability. Knowledge about transmission of COVID-19 and other disease by aerosols emphasizes the importance of interventions such as distancing, masks, and good ventilation.
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