Strategies for Respiratory Droplet Removal in Indoor Environments to Mitigate the Spread of Airborne Diseases

Airborne transmission occurs when infected respiratory particles are released through breathing, coughing, or sneezing. Diseases spread this way include COVID-19, SARS, chickenpox, smallpox, tuberculosis, measles, and influenza. Direct inhalation occurs when someone near an infected person breathes in their exhaled respiratory particles. Tiny exhaled droplet nuclei can remain airborne, spread with air currents, and pose a risk even beyond safe distancing. The project aims to hypothesize, test, and evaluate strategies for removing respiratory droplets in indoor environments, with the goal of reducing the spread of airborne infectious diseases. The proposed strategies involve the deployment of electrostatic devices and microscale air purifiers, specifically designed for widespread use in crowded indoor environments. These systems target the capture of a substantial fraction of exhaled respiratory droplets, thereby mitigating the risk of airborne disease transmission. Their performance will be assessed through detailed modeling and evaluation of droplet removal efficiency…. Droplet trajectories will be analyzed using analytical models, while the exhaled breath cloud will be simulated through an unsteady Eulerian CFD analysis of humid airflow. By integrating these complementary approaches, the project aims to achieve a robust prediction of respiratory particle behavior, balancing accuracy with computational efficiency….. Following an initial modeling campaign, the devices will undergo experimental validation in laboratory settings. Multiple testing methods can be employed to assess their effectiveness: (i) aerosol generation using a propylene glycol solution, with particle counters measuring the emitted droplets; (ii) tracer gas experiments (commonly N2O or CO2), which offer simplicity and applicability across various environments when combined with multi-gas analyzers. To account for droplet evaporation, an effect that progressively alters particle dynamics after emission, the team has also developed a novel methodology based on an ultrasonic emitter. This system aerosolizes and disperses particles in a way that closely replicates the dispersion behavior of human-generated respiratory droplets. A patent covering this methodology has already been issued to the PI and the research group (industrial patent no. 102020000032021). The choice of testing techniques will be guided by insights gained from the initial modeling campaign. The engineering team also brings extensive expertise in prototyping, demonstrated by numerous publications in the energy field. This experience will be pivotal in designing and refining droplet-collection devices, such as the Electrostatic Precipitator, which must be optimized to capture droplets efficiently through ionization while remaining safe and energy-efficient. The same expertise will support the development and testing of fan-and-filter systems for droplet removal. Experimental validation will play a crucial role in verifying the accuracy of simulations. This integrated approach will allow models to be progressively refined, accelerate the evaluation of alternative solutions, and ultimately ensure the identification of the most effective strategies. The results of the modeling and experimental analyses will be utilized by the team from the Department of Maternal, Child, and Adult Medical and Surgical Sciences. Their expertise will be critical for evaluating the epidemiological impact of the proposed droplet-removal strategies, with the aim of developing and validating effective countermeasures. Specifically, they will assess the extent to which contagion can be mitigated by lowering droplet concentrations in indoor environments across different infectious diseases. The analysis will also integrate key epidemiological parameters, such as the quanta emission rate, Minimum Infectious Dose (MID), and Median Infectious Dose (ID50).