Following the work of Prather et al. (2020), we calculated the horizontal distances that can be traveled by respiratory droplets generated by coughing. Here, we assume that the particles will follow the flow field measured by Savory et al. (2014) in the horizontal direction. Droplets will evaporate during the transport. we further that coughing droplets are emitted at three different heights - 1.0, 1.5, and 1.7 m above the ground.

The results show that for droplets above 100 microns, the horizontal distance traveled by the droplets before they settle down to the ground are generally within 2.5 m. For droplets with sizes below 100 microns, the horizontal distance increases significantly, which is due to the more significant role of evaporation that increases the residence time of droplets in the air.

It is very useful to find a new size boundary to divide droplets and aerosols, and the size of 100 microns recommended by Prather et al. (2020) is an appropriate value.

Reference:
Prather, K.A., Marr, L.C., Schooley, R.T., McDiarmid, M.A., Wilson, M.E. and Milton, D.K., 2020. Airborne transmission of SARS-CoV-2. Science (New York, NY), p.eabf0521.
Savory, E., Lin, W.E., Blackman, K., Roberto, M.C., Cuthbertson, L.R., Scott, J.A. and Mubareka, S., 2014. Western Cold and Flu (WeCoF) aerosol study–preliminary results. BMC research notes, 7(1), p.563.