Simple quantitative assessment of the outdoor versus indoor airborne transmission of viruses and COVID-19

In this paper we develop a simple model of the inhaled flow rate of aerosol particles of respiratory origin i.e. that have been exhaled by other people. A connection is made between the exposure dose and the probability of developing an airborne disease. This allows a simple assessment of the outdoor versus indoor risk of contamination to be made in a variety of meteorological situations. It is shown quantitatively that for most cases, the outdoor risk is orders of magnitude less than the indoor risk and that it can become comparable only for extremely specific meteorological and topographical situations. It sheds light on various observations of COVID19 spreading in mountain valleys with temperature inversions while at the same time other areas are much less impacted.

Automated summary

The paper develops a simple model to assess the inhaled flow rate of aerosol particles of respiratory origin and its connection to the probability of developing airborne diseases. It demonstrates that outdoor contamination risk is generally significantly lower than indoor risk, except for specific meteorological and topographical situations. The research sheds light on COVID19 spreading patterns in mountain valleys with temperature inversions compared to other less impacted areas.