Respiratory aerosols are complex mixtures of organic and inorganic compounds, such as proteins and sodium chloride. Previous studies provide evidence that there is a relative humidity (RH) dependency for airborne disease transmission, specifically that virus viability decreases at intermediate relative humidities (RH). The phase state of respiratory aerosols and droplets has been proposed to play a role in the RH-dependence of virus survival. However, phase changes associated with respiratory aerosols are not well characterized. Furthermore, virus survival studies are often performed within culture growth media with uncharacterized phase transitions. Here, we describe a levitation-based technique to characterize the phase changes associated with levitated droplets of model respiratory compounds (proteins, sodium chloride, and calcium chloride). In addition, we characterize the phase changes of various culture growth media that are commonly used in studies of RH-dependent survival of viruses. Using a dual-balance quadrupole electrodynamic balance to merge respiratory compounds and culture media under variable RH conditions, along with various imaging techniques, we can identify phase transitions. We observe multiple phase change types of interest, including crystal nucleation of the inorganic compounds (efflorescence) and amorphous phase changes (aggregation and gelation). The observations show that organic compounds undergo an aggregation or gelation before inorganic efflorescence. Discussion will focus on the specific methods that are used to conduct this research and the detailed observations about the phase changes of respiratory aerosols and culture media.

Method for studying aerosol phase changes relevant to airborne survival of pathogens

ACS Spring Meeting 2021

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