COVID Might be Spread on the Back of Pollen from Trees

Viruses like COVID-19 might be spread further on the back of pollen from trees — potentially increasing the risk of infection in crowded areas, a study has warned.

Experts from the University of Nicosia, Cyprus, created a computer simulation of a willow tree — a prototypical pollen emitter — and modelled how its grains spread.

In a light breeze, the model showed that pollen could pass through a crowd 66 feet away within just one minute, potentially helping move viral particles along the way.

Based on the findings, the authors have said that the six-foot social distance often recommended to cut the risk of spreading COVID-19 might not always be enough.

Instead, they said, recommendations might be improved by adding in accommodation for local pollen levels, especially in crowded areas with trees.

On a heavy day, the average tree can put into the air more than 40 pollen grains per cubic feet, the experts said, with each grain able to carry hundreds of viral particles.

The study was undertaken by computational physicist Talib Dbouk and engineer Dimitris Drikakis of the University of Nicosia.

Their investigation was inspired by the observation of a correlation between areas of increased COVID-19 infection rates and the US national allergy map.

The duo used cutting-edge fluid dynamics models to create a computer simulation of how pollen moves through the air from a willow tree in the wind.

‘One of the significant challenges was the re-creation of an utterly realistic environment of a mature willow tree,’ said Dr Dbouk.

‘This included thousands of tree leaves and pollen grain particles, hundreds of stems and a realistic gathering of a crowd.’

Specifically, the team simulated how 10,000 grains of pollen blowing from their tree would interact with two outdoor gatherings around 66 feet away — one of 10 people, the other of 100 — with some of the individuals also shedding COVID-19 particles.

Having tuned the model’s conditions to match the temperature, windspeed and humidity of a typical spring day in the United States, the duo found that pollen would pass through both crowds in less than a minute.

This, they explained, has the potential to pick up viral particles and carry them further than they would spread otherwise — increasing the risk of infection for people within the range of the tree.

‘To our knowledge, this is the first time we show through modelling and simulation how airborne pollen micro-grains are transported in a light breeze, contributing to airborne virus transmission in crowds outdoors,’ said Professor Drikakis.

Alongside calling attention to unexpected ways in which viruses like COVID-19 might be transmitted, Professor Drikakis and Dr Dbouk said that they hope their study will stoke further interest in the fluid dynamitic of plants.

With their initial study complete, the duo are now looking to better understand the interactions between airborne pollen grains and the human respiratory system under different environmental conditions.

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