Using a computer model, scientists at IIT Bombay have shown that a hotter and drier weather is linked to lower survival chance of the novel COVID-19 on surface, a finding that may lead to better sanitisation guidelines for public places all around the world.
The study, published in the journal physics of Fluid, asessed how long COVID-19, remains viable for infection after anyone with Coronavirus coughs or sneezes.
In order to calculate this, researchers from IIT Bombay, examined the drying time of respiratory droplets from infected patients on various surfaces in six cities around the world, including Singapore and New York.
These respiratory droplets, which are about the size of width of a single human hair, are expelled from the nose or mouth when a Coronavirus infected patient sneezes, coughs or even speaks moistly, the study noted.
Once the respiratory droplets carrying the Coronavirus evaporate, the scientists said the residual Coronavirus becomes inactive, so the transmission and survival of Coronavirus are directly impacted by how long the respiratory droplets remain intact.
Based on their analysis, the researchers said the growth rate of Coronavirus is weakly linked to the outdoor weather, adding that the chances of the survival of the Coronavirus increases roughly by five times under a humid condition as compare to any dry condition.
In the research, the scientists used a mathematical model to assess the drying time for the respiratory droplets under several conditions and showed that ambiant temperature, humidity and the type of surface play critical roles.
Citing an example, the researchers said ambient temperature helped to dry out the respiratory droplets fatser, and drastically reduced the chances of survival of Coronavirus.
The researchers also added that in places with greater humidity, the respiratory droplets stayed on surfaces longer, and the Coronavirus survival chances improved.
Researchers also determined the respiratory droplet drying time in different outdoor weather conditions and examined if this data connected to the growth rate of the Coronavirus in six major cities across the world - New York, Los Angeles, Miami, Singapore and Sidney.
When the researchers plotted the growth rate of Coronavirus infected patients in these places with the drying time of a typical droplet, they got that in the cities with a larger growth rate of COVID-19 pandemic, the drying time was longer.
In a way, that could explain whether slow or fast growth of the COVID-19 infection in a particular city. This may not be the sole factor, but definitely, the outdoor weather matters in the growth rate of the Coronavirus infection, said Rajneesh Bhardwaj, one among the co-authors of the research.
Reasoning COVID-19 survival in a drying respiratory droplet could be helpful for other transmissible disease that spread via respiratory droplets, just like influenza A, said Amit Agrawal, another author of the research.
Citing the limitations of the research, the researchers said they assumed air to be stationary in their model along with the consideration the water droplets evaporation time is expected to reduce in the presence of air currents.
The value of the predicted water droplets evaporation times is on the conservative side, and the actual water droplets evaporation time will be smaller than that obtained here, the researchers noted in the study.
Despite these drawbacks in the model, researchers believe that surfaces like cotton, wood and mobile screens should be cleaned more often than the steel and glass surfaces since the latter are relatively hydrophilic, and the respiratory droplets evaporate on these materials.