size does matter

Aerodynamics of COVID-19 virus aerosols


Aerodynamic characteristics of COVID-19 virus aerosols for future prevention and control measures decision-makings

Despite of the SARS outbreak in 2003, studies on the aerosol transmission mechanism is still very scarce, and thus when the large scale COVID-19 virus human-to-human transmission epidemic outbreak happened beyond the normal droplets or contact transmission scenarios, great attention is needed on the possibility and mechanism of aerosol transmission. Nevertheless, even though numerous studies with the COVID-19 pandemics have been done so far, the lacking of direct evidence on the aerosol transmission is the main reason for agencies to take long-term stringent measures on social distancing. As such, understanding the aerosol transmission is critically important for the prevention and control of COVID-19, environmental protection in medical work, and effective blocking of transmission routes.

New study on the relationship of the movement of air and COVID-19 virus aerosols fills important gaps of knowledge

In a joint study with Wuhan University, Shanghai Environmental Monitoring Center, Fudan University and The Chinese University of Hong Kong, Prof Zhi NING of HKUST and his team was engaged in studying:

  1. Real world RNA concentration of COVID-19 virus aerosol in patient area, medical staff area, public area and its relationship with patient activities, ventilation conditions;
  2. Size distribution of COVID-19 virus aerosol and possible aerosol transmission modes in the air; and
  3. Natural deposition rate of COVID-19 virus on the object surface.

Thirty-five aerosol samples of three different types (total suspended particle, size segregated and deposition aerosol) were collected in (1) Patient Areas and (2) Medical Staff Areas of Renmin Hospital of Wuhan University (Renmin) and Wuchang Fangcang Field Hospital (Fangcang), and (3) Public Areas in Wuhan, China during COVID-19 outbreak. A robust droplet digital polymerase chain reaction (ddPCR) method was employed to quantitate the viral COVID-19 virus RNA genome and determine aerosol RNA concentration.

key findings and Conclusions

The ICU, Coronary Care Unit and general patient rooms inside Renmin, patient hall inside Fangcang had undetectable or low airborne COVID-19 virus concentration, but deposition samples inside ICU (on the floor 2-3 meters away from the patient bed) and air sample in Fangcang patient toilet tested positive.

The airborne COVID-19 virus in Fangcang Medical Staff Area had bimodal distribution –– "sub-micron aerosols" (0.25-0.5 μm aerodynamic diameter) probably from protective apparels and super-micron aerosols (>2.5 μm aerodynamic diameter) probably the resuspension of dust particles from the floors or other hard surfaces –– with a higher concentration than those in Renmin during the outbreak but turned negative after patients number reduced and rigorous sanitization implemented.

Public Areas had undetectable airborne COVID-19 virus concentration but obviously increased with accumulating crowd flow (such as one crowd gathering site about 1 meter to the entrance of a department store).

Room ventilation, open space, proper use, and disinfection of toilets can effectively limit aerosol transmission of the COVID-19 virus. Gathering of crowds with asymptomatic carriers is a potential source of airborne COVID-19 virus. The virus aerosol deposition on protective apparel or floor surface and their subsequent re-suspension is a potential transmission pathway and effective sanitization is critical in minimizing aerosol transmission of COVID-19.

Hear from Prof. Zhi Ning