  The globally supported social distancing rules to prevent airborne
transmission of COVID-19 assume small saliva droplets evaporate fast and large
ones, which contain most viral copies, fall fast to the ground. However, during
evaporation, solutes distribute non-uniformly within the droplets. We developed
a numerical model to predict saliva droplet drying in different environments.
We represent saliva droplets as a solution of NaCl mixed with water. In a hot
and dry ambiance, the solutes form a shell on the droplets' surface, producing
light, hollow particles. These hollow particles have a larger cross-sectional
area compared to their solid counterparts and can float longer and travel
farther in the air. We introduced the "hollowness factor," which serves as a
measure of the ratio of the volume of a hollow particle and the volume of a
solid residue formed during droplet drying. Through our investigations, we
determined that under specific conditions, namely an ambient humidity level of
10% and a temperature of 40{\deg}C, the highest hollowness factor observed was
1.610. This finding indicates that in the case of hollow particle formation,
the droplet nucleus expands by a factor of 1.610 compared to its original size.
