Impact of thermal stratification on airborne transmission risk of SARS-CoV-2 in various indoor environments

There exist various vertical temperature gradients in different-type buildings. A holistic understanding of the impact of different temperature-stratified indoor environments on infection risk is necessary. In this work, the airborne transmission risk of SARS-CoV-2 in different thermally stratified indoor environments is assessed using our previously developed airborne infection risk model. Results show that the vertical temperature gradients in office building, hospital, classroom, etc. are within the range of −0.34 to 3.26 ℃/m. In large space such as coach station, airport terminal, and sport hall, the average temperature gradient ranges within 0.13–2.38 ℃/m in occupied zone (0–3 m); in ice rink with special requirements of indoor environment, the temperature gradient is higher than those in the above indoor spaces. The existence of temperature gradients causes multi-peaks of the transmission risk of SARS-CoV-2 with distancing, and our results show that in office, hospital ward and classroom, the second peak of the transmission risk is higher than 10⁻³ in most contact scenarios, while most being lower than 10⁻⁶ in large spaces like coach station and airport. The work is expected to provide some guidance on specific intervention policies in relation to the types of indoor environments.