Effects of temperature, humidity, and air saturation state on the transmission risk prediction of COVID-19 in typical scenarios (preprint)

Environmental parameters have a significant impact on the spread of respiratory viral diseases. Temperature and relative humidity are correlated with viral inactivation in the air, whereas supersaturated air can promote viral deposition in the respiratory tract. This study introduces a new concept, the dynamic virus deposition ratio (α), that reflects the dynamic changes in particle size and viral deposition under varying ambient environments. Moreover, a non-steady-state modified Wells-Riley model is established to predict the infection risk of shared air space under varying environmental parameters, including temperature, relative humidity, and air saturation state. The quanta emission rate of an asymptomatic infector during different respiratory activities (breath, voice, and cough) are explored, and the differences in the infection risk under saturated and unsaturated air conditions are also compared. Finally, six typical exposure scenarios from daily life are also explored, highlighting scenarios of higher risk. The results show that the highest infection risk (R max =5.2%) and the longest risk duration (T terminal =6.8h) are both reached in cold and damp conditions. This study quantitatively reflects how environmental parameters are linked to viral inactivation and particle deposition, affecting transmission risk.

Analysis on The Risk of Respiratory Virus Transmission By Air Conditioning System Operation-Based on Experimental Evidence (preprint)

It is important to know whether SARS-CoV-2 is spread through the air-conditioning systems. Taking the central air-conditioning system as an example, we analyze the mechanism and potential health risk of respiratory virus transmission in air-conditioned rooms, and propose a method to study the risk of virus transmission in central air-conditioning systems by investigating the data from medical experiments. The virus carrying capacity and the decay characteristics of indoor pathogen droplets are studied in this research. Additionally, the effects of air temperature and relative humidity on the virus survival in the air or on surfaces are investigated. The removal efficiency of infectious droplet nuclei by air-conditioning filter was then determined. Thus, the transmission risk during the operation of centralized air-conditioning system is evaluated. The results show that the indoor temperature and humidity are controlled in the range of 20-25℃ and 40%-70% by central air-conditioning during the epidemic period, which not only benefits the health and comfort of residents, but also weakens the vitality of the virus. The larger the droplet size, the longer the viruses survive. Since the filter efficiency of air-conditioning filter increases with the increase of particle size, increasing the number of air changes of the circulating air volume can accelerate the removal of potential pathogen particles. Therefore, scientific operation of centralized air conditioning systems during the epidemic period has more advantages than disadvantages.