Impact of high-altitude conditions and low ambient pressure on saliva evaporation rate and airborne transmission of viruses

Understanding saliva droplet behavior under high-altitude, low-pressure conditions are essential for evaluating virus transmission risks in aircraft cabins. This study investigated saliva evaporation dynamics at the High Altitude Research Station Jungfraujoch (at 3580 m), simulating aircraft cabin conditions, and compared results with prior study results (at 300 m). Experimental measurements revealed that saliva's relative evaporation rate (RER) to water increased from 0.8569 at ground level to 0.9722 at high altitude. Residue-to-initial droplet size ratios were also higher at the high altitude (0.2522 against 0.2157). Numerical modeling, incorporating saliva droplet properties and viral loads, demonstrated significantly prolonged airborne lifetimes of saliva droplets exhaled by coughing, sneezing, and talking and airborne RNA which is high potential infectious at high altitudes. These findings underscore the critical role of environmental factors, especially ambient pressure and altitude in influencing airborne transmission dynamics in aircraft-like conditions. Combining experimental and numerical approaches, this study provides key parameters for computational fluid dynamics (CFD) simulations of virus transmission in aircraft cabin conditions. These findings highlight the importance of optimized environmental controls, such as ventilation and humidity regulation, to mitigate airborne viral spread in confined spaces like aircraft cabins.