Crossing scales to assess the risks of viral transmission in a crowd
A chasm of several orders of magnitude in lengthscales separates viruses and the respiratory droplets carrying them from the typical distances over which a crowd evolves. Therefore, it does not come as a surprise that spanning this gap to get a robust assessment of the risks of short-range viral transmission in a crowd is a major theoretical and numerical challenge. That being said, such a junction is necessary, because both the details of the microscopic propagation of droplets and the motion of people in the crowd drastically affect the air-borne transmission of viral carriers.
With Simon MENDEZ (CNRS / IMAG), we proposed a computationally efficient and versatile method to bridge this gap, via the generation of coarse-grained dynamic maps of aerosol concentrations around any potential emitter. This method was applied to (mostly outdoor) empirical situations with crowds, using field data, and enabled us to rank the situations by the risks of viral transmission that they raise. Aa a by-product of this detailed study, the dramatic effects of even light winds and air flows on transmission risks was quantitatively ascertained.
The paper was published in Advanced Science and is openly accessible.