Following the outbreak of coronavirus in Wuhan, China in early 2020, millions of people flocked to buy face masks to protect themselves from the virus. Data shows face masks can protect you from the coronavirus, but is there something closer to home that can help – do air purifiers also capture coronavirus particles?
What’s in Your Typical Air Purifier?
Most air purifiers are made up of two things: a fan and a filter. They’re as simple as that.
Most of us understand how fans work, but how about the filter? The filter – typically a HEPA filter – is the workhorse of any purifier. Turns out they’re nothing fancy either. They were , and they’re just a mat of synthetic fibers. That can capture over 99% of tiny air pollution particles.
But how small is the coronavirus? And what’s the smallest particle size a HEPA filter can capture? Let’s break this into two questions:
How Small Are Coronavirus Particles?
The 2019 Novel Coronavirus, or 2019 nCoV, is a new respiratory virus first identified in Wuhan in China’s Hubei Province. Scientists have already taken electron microscope images to measure the size of coronavirus “virions” (or particles). The virions are spherical particles with diameters of approximately 125 nm (0.125 microns). The smallest particles are 0.06 microns, and the largest are 0.14 microns.
That makes the coronavirus particles smaller than PM2.5 particles, but bigger than some dust particles and gases.
Can HEPA Filters Capture Particles As Small As The Coronavirus?
If we look to the definition of HEPA filters on Wikipedia, it says HEPA filters must remove: “99.97% of particles that have a size greater than or equal to 0.3 µm.”
It only mentions particles 0.3 microns and above. So what about smaller particles the same size as the coronavirus? Can HEPA filters capture these?
This exact question has led to years of confusion and false advertising claims about HEPA filters, such as this one, so let’s get to the bottom of it.
And this confusion is now leading to more misinformation during the spread of information during the coronavirus outbreak:
Why Our Intuitions About Air Purifier Filters Are Wrong
The answer is surprising. It’s surprising because our intuition about filters is wrong. Like most people, I had the intuition that HEPA filters work like a net.
If a particle is smaller than the holes in the net, it gets through. Makes sense! However, it turns out that particles as small as the coronavirus, and other nano-particles get captured using a scientific phenomenon called diffusion.
Diffusion is surprisingly effective at capturing tiny virus-sized aprticles. According to NASA, HEPA filters capture “virtually 100% of particulates.”
Researchers at the University of Minnesota tested this question with weaker fiberglass furnace filters and higher-grade HEPA filters. In their test, they shot particles of silver from 3 to 20 nanometers at the filters (that’s between 3 to 20 times smaller than coronavirus particles).
The results showed that filters captured 99.99% of particles smaller than 5 nanometers. Bingo! HEPA filters (and even lower-grade filters like furnace filters) are incredibly effective at capturing smaller sized particles such as the coronavirus.
What Does This Mean for The Coronavirus?
If you’re living in a common house, or you’re working in an office or school with a large number of employees, turning on your air purifier can help filter out any virus-sized particles in the air, potentially reducing the chance of transmission. HEPA filters, in one pass, can be expected to filter out over 99% of the coronavirus.
Bottom Line: Can Air Purifiers Capture The Coronavirus?
Air purifiers that contain HEPA filters or even lower grade filters can capture virtually all sizes of solid particles, including particles 0.1 microns in diameter – or the same size as the coronavirus. If you’re living in a shared house, or are working in a closed environment with lots of people, turning on an air purifier could help reduce spread of the coronavirus.
For those in places with central air (HVAC) system, make sure the systems contain filters and are well maintained. If your HVAC contains no filters, installing air purifiers in each room could still help reduce the spread of viruses.
Paddy graduated in aeronautical engineering from Bristol University, and now runs Smart Air’s operations from Beijing. He’s an advocate for open data, free information and transparent business.