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As people spend more time together indoors with the changing of the seasons, could an air cleaner provide an added layer of protection against the transmission of the novel coronavirus by removing a percentage of viral particles from the air.
Ben de la Cruz/NPR
Ben de la Cruz/NPR
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VIDEO: How To Protect Yourself From Coronavirus That Can Linger In The Air
Exactly how much the air cleaners help is somewhat up for debate, but Richard Corsi, dean of the college of engineering and computer science at Portland State University, has been running models and testing portable air cleaners that show clear benefits, dropping particle levels significantly in a large bedroom in his own home.
So why have some medical doctors questioned whether portable air cleaners can remove the virus at all?
They’re simply wrong, Corsi and Allen say. In fact, they’re wrong in two ways, Allen says. HEPA filters remove at least 99.97% of airborne particles with a size of .3 microns — and even more particles of other sizes — whether smaller or bigger.
«And the virus is never naked in the air,» he says.
While the virus itself is about .1 microns in size, or 1/1000th of a cross-section of human hair, it’s released into the air embedded in a particle of mucus and saliva, Corsi says. «It can’t survive outside that particle,» he says. «And those particles are easily removed by HEPA filters.»
Of course, portable air cleaners are not a magic bullet. They’re an added layer of protection — «not a substitution for everything else. And that would not change how much I practice all the other things,» says Abraar Karan, a Harvard Medical School physician. «We know that masks and distancing are both important — but if it’s spread by aerosols, staying six feet away from people may not be adequate.»
To put it in numerical terms: Masks offer at least a 50% risk reduction, Corsi says. A personal air cleaner might reduce that another 50%, for a total risk reduction of 75%. Increased ventilation could get the reduction to 85 or 90%. But if you take off the mask, that percentage plummets.
How to buy a PAC
Look for a unit with a HEPA filter and a clean air delivery rate (CADR) of 300 cubic feet per minute (not hour) or better — and not much else, Corsi says. «You don’t need any other gadgets,» he says. In fact, extra bells and whistles can sometimes produce ozone, so it’s best to keep it simple. To calculate what size you need for your space, use this tool that Allen helped develop for classrooms — it works equally well for homes, he says. Prices are in the $250 range.
How to use it
Again, this will depend on your individual situation. In general, place the air purifier near the person whose germs you want to avoid (the bedroom of someone who is sick with COVID-19, for example). When Corsi hosted a relative who works in care homes, he and his wife ran a portable air cleaner in their guest room and downstairs — in addition to wearing masks and opening windows. They added a fan — blowing air outward — to their guest room.
The only downside to a personal air cleaner is the cost (in addition to the upfront cost, there’s the cost of replacement filters and energy to consider). When you’re considering the purchase, think of it as a health care tool, Allen suggests. And remember that personal air cleaners also remove chemicals, allergens and dust.
For Abraar, even without randomized, controlled trials to prove that portable air cleaners help prevent COVID-19, it’s a simple calculation for most people who aren’t completely isolated.
«At this point, the possible benefits outweigh the cost,» he says. «If later the studies prove air purifiers work and it may have had an impact, you don’t want to think, ‘I could have gotten it.’ «
Sheila Mulrooney Eldred is a freelance health journalist in Minneapolis. She’s written about COVID-19 for Medscape, Mpls.St.Paul Magazine, Science News for Students and the Washington Post. More at sheilaeldred.pressfolios.com. On Twitter: @milepostmedia
- air cleaning machine
- aerosol transmission
- COVID-19 transmission