Modeling the Impact of Indoor Relative Humidity on the Infection Risk of Five Respiratory Airborne Viruses

Abstract

With a modified version of the Wells-Riley model, we simulated the size distribution and dynamics of five airborne viruses (measles, influenza, SARS-CoV-2, human rhinovirus, and adenovirus) emitted from a speaking person in a typical residential setting over a relative humidity (RH) range of 20 to 80 % and air temperature of 20-25 °C. Besides the size transformation of virus-containing droplets due to evaporation, respiratory absorption and then removal by gravitational settling, the modified model also considered the removal mechanism by ventilation. The trend and magnitude of RH impact depended on the respiratory virus. For rhinovirus and adenovirus humidifying the indoor air from 20/30 % to 50 % will be increasing the relative infection risk, however, this relative infection risk increase will be negligible for rhinovirus and weak for adenovirus. Humidification will have a potential benefit in decreasing the infection risk only for influenza when there is a large infection risk decrease for humidifying from 20 % to 50 %. Regardless of the dry solution composition, humidification will overall increase the infection risk via long-range airborne transmission of SARS-CoV-2.Compared to humidification at a constant ventilation rate, increasing the ventilation rate to moderate levels 0.5 → 2.0 h−1 will have a more beneficial to infection risk decrease for all viruses except for influenza. Increasing the ventilation rate from low values of 0.5 h−1 to higher levels of 6 h−1 will have the dominating effect on reducing the infection risk regardless of virus type.

Proposal and application of indexes for dynamic evaluation of indoor humidity and thermal environment

“…In addition, larger plants produce more water-vapor 4 . When a source continuously releases large amounts of wet-components, humidity increases rapidly, which can produce dew and mold on the walls 5 , cause respiratory discomfort and allergies [6][7][8] , and increase the infection risk of in uenza or SARS-Cov-2 [9][10][11] . When the humidity is overly low (≤ 30%) due to the sources absorbing wet-components, dryness will not only affect the thermal comfort of occupants 12 but also cause respiratory pain 13,14 , eye itching 15,16 and static electricity.…”