Evaporation dynamics of airborne water-based droplets with contaminants*

Accurate measurement of bioaerosol particles is crucial to assess the risks associated with the airborne transmission of pathogens. However, the size of these airborne water-based pathogen-laden particles changes rapidly due to evaporation. The presence of contaminants that affect surface tension and viscosity pose a challenge for accurate prediction of droplet fate. In this study, this phenomenon is investigated experimentally under controlled ambient conditions. Droplets 53 micrometers in diameter are produced using an inkjet printhead and injected in a concurrent flow of pressurized air, under controlled temperatures and relative humidities. The evolution of the droplet size is quantitatively assessed through phase Doppler anemometry. Oil-based droplets are used as a reference as they do not evaporate significantly. Water droplets are then considered, first pure and then contaminated with a surfactant or dissolved Polyethylene glycol, to simulate the properties of potentially contaminated droplets from humans or engineered sources. The results will quantify the discrepancies in the evaporative behavior of solid-containing droplets compared to their pure water counterparts, highlighting how the infection risk is affected by ambient conditions and emphasizing the need to consider evaporation when measuring the size of potentially contaminated droplets.