Δαφνη Ευτυχια Αρθουρος

"Morawska had spent more than two decades advising a different branch of the WHO on the impacts of air pollution. When it came to flecks of soot and ash belched out by smokestacks and tailpipes, the organization readily accepted the physics she was describing-that particles of many sizes can hang aloft, travel far, and be inhaled. Now, though, the WHO's advisers seemed to be saying those same laws didn't apply to virus-laced respiratory particles. To them, the word airborne only applied to particles smaller than 5 microns. Trapped in their group-specific jargon, the two camps on Zoom literally couldn't understand one another.

[...]

"Epidemiologists have long observed that most respiratory bugs require close contact to spread. Yet in that small space, a lot can happen. A sick person might cough droplets onto your face, emit small aerosols that you inhale, or shake your hand, which you then use to rub your nose. Any one of those mechanisms might transmit the virus. 'Technically, it's very hard to separate them and see which one is causing the infection,' Marr says. For long-distance infections, only the smallest particles could be to blame. Up close, though, particles of all sizes were in play. Yet, for decades, droplets were seen as the main culprit.

"Marr decided to collect some data of her own. Installing air samplers in places such as day cares and airplanes, she frequently found the flu virus where the textbooks said it shouldn't be-hiding in the air, most often in particles small enough to stay aloft for hours. And there was enough of it to make people sick.

"In 2011, this should have been major news. Instead, the major medical journals rejected her manuscript. Even as she ran new experiments that added evidence to the idea that influenza was infecting people via aerosols, only one niche publisher, The Journal of the Royal Society Interface, was consistently receptive to her work. In the siloed world of academia, aerosols had always been the domain of engineers and physicists, and pathogens purely a medical concern; Marr was one of the rare people who tried to straddle the divide. 'I was definitely fringe,' she says."

-- Megan Molteni, "The 60-Year-Old Scientific Screwup That Helped Covid Kill", Wired, 2021-05-13 [Long article, but worth reading the whole thing to find out exactly where that 5 μm threshold idea came from!]