Ken is right! While running with others, the six foot rule is a poor guideline. The breath of a person ahead is entrained into that person's slipstream and persists well beyond six feet. In absence of a strong wind or at least a mild crosswind, the person behind runs into the breath of the person ahead, like railroad cars behind Thomas the Tank Engine. We need to learn to be as aware of the wind as is a deer.
The basic conclusion of the paper is that if you are running in the slipstream of another runner you should be 10 meters or more back
. You can get the idea by looking at Fig. 12 in the preprint, "Towards aerodynamically equivalent COVID-19 1.5 m social distancing for walking and running", by B. Blocken, F. Malizia, T. van Druenen, T. Marchal: http://www.urbanphysics.net/COVID19.html
Fig. 12 of Blocken preprint
Bert Blocken, the aerodynamics guy who wrote the paper, is in a group at Eindhoven University of Technology (in the Netherlands) that does some cool stuff (http://www.urbanphysics.net/index.html
) about aerodynamics of bicyclists, as well as air flow in buildings.
For those technically inclined, here's a non-specialist overview of how droplets behave in air, as they diffuse, fall, and evaporate to smaller size: https://arxiv.org/abs/2003.13689
(just in case you were wondering...)
Be aware of the wind direction, visualize slipstreams, and keep 10 meters apart if not running into clean air!