COVID-19: Effects of Environmental Conditions on the Propagation of Respiratory Droplets

Abstract

As coronavirus disease 2019 (COVID-19) continues to spread, a detailed understanding on the transmission mechanisms is of paramount importance. The disease transmits mainly through respiratory droplets and aerosol. Although models for the evaporation and trajectory of respiratory droplets have been developed, how the environment impacts the transmission of COVID-19 is still unclear. In this study, we investigate the propagation of respiratory droplets and aerosol particles generated by speech under a wide range of temperatures (0–40 °C) and relative humidity (0–92%) conditions. We show that droplets can travel three times farther in low-temperature and high-humidity environment, whereas the number of aerosol particles increases in high-temperature and low-humidity environments. The results also underscore the importance of proper ventilation, as droplets and aerosol spread significantly farther in airstreams. This study contributes to the understanding of the environmental impact on COVID-19 transmission.

SARS-CoV-2 and Health Care Worker Protection in Low-Risk Settings: a Review of Modes of Transmission and a Novel Airborne Model Involving Inhalable Particles

“…These droplets are thought to be the main mode of transmission of COVID-19 (1), and they typically travel 1 to 2 m before landing on surrounding surfaces. However, they may be propelled further in the presence of ventilation (2) or forceful ejection (e.g., a violent sneeze) (3) and under certain environmental conditions (e.g., cool and humid) (4). The SARS-CoV-2 virus is also thought to be transmitted by direct contact person to person (e.g., exchange of saliva or a handshake) or by indirect contact through intermediate objects (e.g., sharing of cups, doorknobs).…”

Association between climate and new daily diagnoses of COVID-19

“…Second, longer sunlight exposure and higher outdoor temperature have also been associated with greater extent of viral inactivation (18, 19). Finally, reliable evidence has been provided that virus-containing droplets could travel 3-fold slower in higher temperature environments (20), thus consistently mitigating their air propagation and infective potential.…”

“…Background airspeed seems to be another important determinant of infectious disease transmission. Although it is quite understandable that viral-containing aerosols and droplets may propagate over longer distances as the airflow speed increases, it has also been demonstrated that higher air velocity may effectively dilute the number of infectious viral-containing particles (7, 20). In keeping with this theory, a decreased wind speed has been inversely associated with the number of COVID-19 cases in five major Saudi Arabian cities (21).…”

“…Finally, concerning humidity, Zhao et al recently showed that air transmission of virus-containing droplets is directly associated with humidity, increasing almost in parallel with the extent of environment humidity (20). Interestingly, these same authors concluded that the current 1 to 2 meters social distance standards might be insufficient in many ambient conditions, because droplets may travel far beyond such distances in extremely humid and cold environments.…”

The role of airborne particles and environmental considerations in the transmission of SARS-CoV-2

“…People may also become infected through physical contact of virus-contaminated objects such as solid waste ( Al Huraimel et al, 2020 , Ben-Shmuel et al, 2020 , Suman et al, 2020 ). Aerosol transmission in a relatively closed environment ( Azuma et al, 2020 , Zhao et al, 2020 , Tung et al, 2021 ), such as hospital locals have been confirmed ( Shi et al, 2020 ). In addition, environmental pollution caused by feces and urine aerosols ( Heller et al, 2020 ) or physical contact in toilets ( Hoseinzadeh et al, 2020 , Mehraeen et al, 2020 , Pamplona et al, 2020 ) could pose a major transmission risk.…”