Airborne transmission during short-term events: Direct route over indirect route

Xiujie Li, Zhengtao Ai, Jinjun Ye, Cheuk Ming Mak, Hai Ming Wong

Research output: Journal article publicationJournal articleAcademic researchpeer-review

14 Citations (Scopus)


Numerous short-term exposure events in public spaces were reported during the COVID-19 pandemic, especially during the spread of Delta and Omicron. However, the currently used exposure risk assessment models and mitigation measures are mostly based on the assumption of steady-state and complete-mixing conditions. The present study investigates the dynamics of airborne transmission in short-term events when a steady state is not reached before the end of the events. Large-eddy simulation (LES) is performed to predict the airborne transmission in short-term events, and three representative physical distances between two occupants are examined. Both time-averaged and phase-averaged exposure indices are used to evaluate the exposure risk. The results present that the exposure index in the short-term events constantly varies over time, especially within the first 1/ACH (air changes per hour) hour of exposure between occupants in close proximity, posing high uncertainty to the spatial and temporal evolutions of the risk of cross-infection. The decoupling analysis of the direct and indirect airborne transmission routes indicates that the direct airborne transmission is the predominated route in short-term events. It suggests also that the general dilution ventilation has a relatively limited efficiency in mitigating the risk of direct airborne transmission, but determines largely the occurrence time of the indirect one. Given the randomness, discreteness, localization, and high-risk characteristics of direct airborne transmission, a localized method that has a direct interference on the respiratory flows would be better than dilution ventilation for short-term events, in terms of both efficiency and cost.

Original languageEnglish
JournalBuilding Simulation
Publication statusAccepted/In press - 2022


  • airborne transmission
  • direct exposure
  • exposure risk
  • short-term events
  • transient computational fluid dynamics (CFD)

ASJC Scopus subject areas

  • Building and Construction
  • Energy (miscellaneous)


Dive into the research topics of 'Airborne transmission during short-term events: Direct route over indirect route'. Together they form a unique fingerprint.

Cite this