Evaporation of Respiratory Droplets Is Crucial in Coronavirus Transmission

With COVID-19 cases continuing to rise worldwide, it is now more crucial than ever to understand other factors that may affect the viability of the virus. Understanding how the climate can affect virus spread is more critical than ever as the winter approaches.

In the paper, Physics of Fluids, by AIP Publishing, researchers delved into the effects of relative humidity, environmental temperature, and wind speed on the viability of the virus. They found out that the drying time, evaporation of the respiratory droplets from a COVID-19 infected subject is critical in transmitting the infected particles.

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One of the authors of the paper, Dimitris Drikakis, said that by having a better understanding of evaporation and its effects on the climate, predicting the virus concentration or potential of survival can be done more accurately.

Despite the importance of airborne droplet transmission, there have been little studies done on the heat and mass transfer within respiratory droplets.

The researchers developed theoretical correlations regarding the unsteady evaporation of saliva droplets laden with coronavirus. They implemented the theory in an advanced computational fluid dynamics platform and studied how weather conditions can affect airborne virus transmission.

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Co-author Talib Dbouk said that with a high temperature and low relative humidity, there is a high evaporation rate of infected saliva droplets, which significantly reduces the virus viability. 

However, the researches observed that in areas with high temperature and humidity, the droplet cloud's travel distance and concentration continued to be significant. The speed at which the wind travels is another crucial factor that may change the rules for the social distancing guidelines.

These findings can help explain why the hot and humid weather conditions in Delhi and other crowded cities worldwide saw an increased number of coronavirus cases in July. This also warns of a possibility for a second wave of the pandemic with the coming autumn and winter seasons where the low temperatures and high wind speeds can increase how the virus is transmitted and prolong its survival. 

Winter Season and Coronavirus

During the cold, dry, winter weather, the mucous linings in our noses dry up, impairs the function of the cilia (tiny hairs lining the nasal passage) to clear viruses from the nose. This may be the reason why more people are susceptible to the virus during the colder seasons.

When the cold, dry air meets warm air from indoors, it reduces the humidity of the air by up to 20%. This lower humidity levels aid in the spread of virus aerosols and could make the virus more stable. 

In another study on how temperature and humidity affect coronavirus, it is shown how high temperatures and humidity have a synergistic effect on the inactivation of SARS CoV viability while lower temperatures and moisture prolong the survival rate of the virus on contaminated surfaces.  

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