Cough drops travel longer in cold and humid – new Covid model

The researchers describe the early spread of respiratory viruses, including Covid-19, and a new mathematical model that can be used to predict the role of respiratory droplets in that spread. (File photo)

A new study shows that respiratory droplets from coughs and sneezes travel longer and last longer in cold, humid climates than in dry, hot climates.

This study, conducted by researchers at the University of California San Diego (UCSD) Indian Institute for Science (Bengaluru) and University of Toronto, is published in the Physics of Fluids journal.

How do you reach these findings?

Researchers describe a new mathematical model they say can be used to predict the initial spread of respiratory viruses COVID-19, And the role of respiratory droplets in its spread. The model is a combination of droplet physics and spread. Pandemic It is based on population size interactions. Find out how fast the splash spreads and how long it lasts.

“We’ve included a detailed kinetic model for infection as droplets migrate/evaporate,” said Saptarshi Basu of IISc, one of the study authors. Indian Express.. “It is based on the molecular collision theory adopted from combustion. The key to this work is to correlate the physics of droplets with the kinetics of infection to arrive at a reaction or infection rate and subsequent growth. did.”

Modification from Saha et al / Physics of Fluids

Collision theory predicts the rate of chemical reactions based on the frequency of collisions between molecules. “The frequency with which a healthy person comes into contact with an infected droplet cloud can measure how quickly the disease spreads,” said Professor Abhishek Saha of UCSD, one of the study authors, in a statement.

The team applied a model of chemical reactions and physics using droplets of saline solution (saliva is often sodium chloride) on levitation devices to determine the size, spread, and lifetime of these particles under different environmental conditions. Decided.

So how far does the droplet move?

It has been found that, depending on the weather conditions, some respiratory droplets travel 8 to 13 feet from the source before they evaporate. At 35°C and 40% relative humidity, droplets can travel about 8 feet. However, at 41°F and 80% humidity, droplets can travel up to 12 feet. This all doesn’t even consider the wind.

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This is 6 feet without a mask Avoid crowds Researchers said it may not be enough to prevent the infection.

Need to worry about winter?

Bass says the life of the droplet depends more on humidity than on temperature. “This means that at high humidity (relative humidity), it lasts longer, so it has a longer distance to evaporate or settle. Also, low temperatures extend life, but not as much as humidity. “He said.

Are there any other important findings?

This study provides a droplet size range with greater risk. Droplets in the 14-48 micron range have been found to evaporate and take longer to travel longer distances. Small droplets evaporate in a fraction of a second, while droplets larger than 100 microns quickly settle on the ground.

Wearing a mask traps particles within this critical range.

What are the model limits?

In a statement, Professor Swetaprovo Chaudhuri of the University of Toronto mentioned “idealized assumptions” and “variability of some parameters”. Mr. Bass said the next step was to mitigate some simplifications and include various transmission modes.

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