Interpersonal droplet transmission is a rapid routine of spreading of airborne pathogens and subsequently respiratory infectious diseases not only in enclosed indoor spaces but also in semi-open outdoor spaces such as urban street canyons. Among many factors, droplet sizes, background wind speed, and relative humidity greatly affect interpersonal droplet transmission. And social distancing is also confirmed to be an effective method to prevent the transmission of virus between citizens.
This study uses four droplet sizes: 10μm, 25μm, 50μm, and 100μm; two background wind speeds: 3 m/s and 13 m/s, three relative humidity: RH=35%, 60%, and 95%, and four separation distances between two persons: D=0.5m, 1m, 2m, 4m to investigate the effects of these factors on interpersonal droplet transmission in a deep and narrow street canyon using computational fluid dynamics (CFD) simulation.
The results revealed low-speed background wind moves droplets upward and suspends them in the air for a longer time while high-speed background wind uniformly distributes droplets without relating them for longer periods in the street canyon. Furthermore, droplets with smaller diameters and dry air allow droplets to travel longer distances and deposit on the surrounding buildings’ walls or be suspended in the air. In contrast, larger droplets and moist air decrease the interpersonal droplet transmission by forcing rapid deposition of droplets either on the ground or the infected person’s body, who exhaled contaminated droplets. Moist air renders low viral inhalation and deposition to the susceptible person. While in dry condition, safe distances of 4m and 2m are recommended under low and high background wind speed respectively.
 

urban street canyon,interpersonal droplet transmission,CFD simulation,Speaking,Social distancing