On today’s episode of “Is nothing sacred?”, COVID-19 has now cast a pall over the prospect of spring, with a new study suggesting that tree pollen can carry SARS-CoV-2 particles further and facilitate the spread of the virus.
In a paper in Physics of Fluids, Talib Dbouk and Dmitris Drikakis of the University of Nicosia, Cyprus, decided to investigate the possibility after noticing a correlation between COVID-19 infection rates and pollen concentrations on the US National Allergy Map.
Pollen exposure can weaken the immune system against certain viruses, but the study’s authors say that pollen grains can also act as vectors for pathogens, carrying potentially hundreds of virus particles at a time.
The researchers deployed computational modelling of fluid dynamics to mimic the pollen movement from a willow tree, a classic example of a pollen emitter.
They recreated a willow tree, including individual leaves and grains of pollen, simulated outdoor gatherings of 10 to 100 people with some shedding COVID-19 particles, and subjected these virtual ‘groups’ to 10,000 pollen grains.
“To our knowledge, this is the first time we show through modelling and simulation how airborne pollen micrograins are transported in a light breeze, contributing to airborne virus transmission in crowds outdoors,” says Drikakis.
The model was designed to replicate the temperature, wind-speed and humidity of a typical spring day in the US. Under these conditions, the model shows pollen can pass through a crowd in less than one minute.
“One of the significant challenges is the re-creation of an utterly realistic environment of a mature willow tree,” said Dbouk. “This included thousands of tree leaves and pollen grain particles, hundreds of stems and a realistic gathering of a crowd of about 100 individuals at about 20 metres from the tree.”
Based on the modelling, the authors warn a six-foot distance limit may be insufficient to protect crowds in areas with high pollen counts.