The transmission of coronavirus occurs through respiratory droplets, usually from a sneeze or a cough. Recently, researchers have discovered which environment is best for the virus to thrive and how the weather affects COVID-19 droplets.
A team from four universities published their study in the journal Physics of Fluids describing the physics of droplets. A group of international engineers determined that respiratory droplets last longer and travel farther in humid and cold environments compared to hot and dry climates.
Their new mathematical model was used to predict the early spread of respiratory viruses such as the coronavirus. Environmental factors proved to play a major role in droplet spread and how droplet clouds spread respiratory viruses.
Measuring a chemical reaction called collision rate theory, the model analyzes the interaction and collision rates of a droplet cloud when an infected person exhales droplets in a group of healthy people. Their unique model allows them to assess droplet transmission--measuring distance, speed, and how long the droplets last--in a realistic population.
"The basic fundamental form of a chemical reaction is two molecules are colliding. How frequently they're colliding will give you how fast the reaction progresses," said Professor Abhishek Saha from the University of California San Diego. In the same way, "how frequently healthy people are coming in contact with an infected droplet cloud can be a measure of how fast the disease can spread."
Weather Conditions and Coronavirus Droplets
Within various weather conditions, respiratory droplets can travel from 8 to 13 feet before evaporating while factoring in natural wind. If people did not wear masks, a physical distance of 6 feet will not hinder droplet transmission.
Saha explained that droplet physics is completely dependent on the weather. "If you're in a colder, humid climate, droplets from a sneeze or cough are going to last longer and spread farther than if you're in a hot dry climate, where they'll get evaporated faster. We incorporated these parameters into our model of infection spread; they aren't included in existing models as far as we can tell."
At 95 degrees Fahrenheit with 40% relative humidity, droplets can travel as far as 8 feet. If the weather is at 41 degrees Fahrenheit with 80% relative humidity, droplets can travel 12 feet.
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Physics & Aerodynamics
Alongside engineers from UC San Diego Jacobs School of Engineering, University of Toronto, and Indian Institute of Science, they used physics and aerodynamics to analyze respiratory droplets. Using previous models of a saltwater solution, a machine called an ultrasonic levitator was used to determine droplets in various weather conditions since saliva contains high levels of sodium chloride.
The model is based on "first principles" which connects physical laws, said Professor Swetaprovo Chaudhur from the University of Toronto. With their "idealized assumptions," several variabilities in some parameters are still being improved. "Maybe a 'first principle' pandemic model with high predictive capability could be possible" as the experiments include epidemiology practices too.
The nest step is to simplify the model and analyze various modes of transmission, explained Professor Saptarshi Basu from the Indian Institute of Science. Several experiments are being conducted to study how respiratory droplets settle on surfaces.
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