Can Air Purifiers Filter Out The Coronavirus?

Size of coronavirus particle pm2.5 and bacteria

Following the outbreak of coronavirus, 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 can 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.

Read how air purifiers work and how to build your own »

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 invented back in the 1940s, and they’re just a mat of synthetic fibers. What’s important is that they can capture over 99% of air pollution particles.

typical HEPA filter

How Small Are Coronavirus Particles?

But first we need to know how small the coronavirus is. Scientists have already taken electron microscope images to measure the size of coronavirus (Covid-19) “virions” (or particles). The virions are spherical particles with diameters of approximately 0.125 microns. The smallest particles are 0.06 microns, and the largest are 0.14 microns.

Coronavirus virus particle size, can air purifiers capture coronavirus

That makes the coronavirus particles smaller than PM2.5 particles, but bigger than some dust particles and gases.

Size of coronavirus particle pm2.5 and bacteria

Can HEPA Filters Capture Particles As Small As The Coronavirus?

The definition of HEPA filters on is that they must remove 99.97% of particles “greater than or equal to” 0.3 microns.

HEPA filter particle capture size 0.3µm; air purifiers coronavirus

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.

Molekule air purifier review

And this confusion is now leading to more misinformation during the spread of information during the coronavirus outbreak:

coronavirus size too small for masks

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.

HEPA filters - do they capture particles 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.

Learn more about the science behind diffusion and how it captures nano-particles »

Diffusion is surprisingly effective at capturing tiny virus-sized particles. According to NASA, HEPA filters capture “virtually 100% of particulates.”

NASA nanoparticles HEPA capture

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 roughly 5 to 30 times smaller than coronavirus particles).

HEPA Filters Capture Nanoparticles; air purifiers capture coronavirus

The results showed that filters captured 99.99% of particles smaller than 5 nanometers. Bingo! HEPA filters are incredibly effective at capturing nanoparticles–even smaller than the coronavirus.

What Does This Mean for The Coronavirus?

Botton line: HEPA filters can filter out over 99% of the coronavirus in a single pass.

This is important for air travel, because airlines use HEPA filters to clean the air in the cabin.

It’s less clear that this would be useful in a home, office, or school, since there is less recirculated air and viruses often (but not always!) travel on large water droplets, which tend not to linger in the air. However, if there are virus particles in the air entering a purifier, the HEPA filter will filter them out.

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.

Explore more: What types of filters do I need to protect myself from all types of pollutants?


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Martin Lefebvre

Thanks Paddy for this great article,
I would like to add that filtration efficiency should be rated at MPPS (Most penetrating particules size) which vary (10 nm-500 nm) with speed and type of filter (electrostatic or not). A electrostatic filter rated 99,97% at 0.3 um would not garanti the performance at 0.1 um. However, we can suppose that an efficiency of 99% will be achieve in most design.

Fulvio Airaghi

Congratulation for the article! Very clear and complete of reliable citation. Thank you

gtreal

Great! I’ll just buy a filter layered with carbon for my PITTA MASK!!!

Matt

I am an oral surgeon looking for a short term fix until I can incorporate hepa filtration and negative pressure into my rooms. I have not been able to find a NIOSH classification or recommendation for any room based HEPA filtration system. It appears from your article that any air purifying system with a HEPA filter will be an improvement but do you recommend any ?

Liz - Smart Air

Hi Matt, if you are looking for something to clean up your room air efficiently, read this article : https://smartairfilters.com/en/blog/weaker-filter-stronger-purifier/
The point is to get the best CADR you can have out of an air purifier. So check the efficiency instead of just the HEPA grade.

Charlie Thomson

This is absolutely not true and there are serious consequences (risk of infecting patients) to this simplistic view. You miss two main points. 1. particle breakthrough that is a measure and grading system separate from initial efficiency. In the real world two cartridges can have the same high efficiency rating but one will be able to hold the captured particles over time while the other will release them back into the “clean” air coming out of the purifier. 2. the efficiency rating of the cartridges means if the filter is not sealed in the housing. If there is leakage around… Read more »

Sittana

Hi Charlie, I am a dentist too and would like to know your recommendation for HEPA to decontaminate a room between patients?
Thanks in advance

Anne

It would be helpful if you could cite independent research. The question is essentially if some level of filtration is better than none. There is no requirement to provide air filtration at any level in the United States in many, if not most, outpatient medical facilities. Furthermore, unless you create a negative pressure environment, there will be leakage. Its all a cost/benefit trade off.

Clark Todd

Recent articles in US press have touted blue hydro polyester shop towels as n-95 equivalent filtration for home made masks. What is hydro polyester and can you weigh in on this? I’m making homemade masks. Thanks!

Liz - Smart Air

Hi Clark, the shop towel is on our to test list, and we will publish the result as soon as it comes out. Stay tuned!