In this text you can read about air purifiers and viruses. Two questions are discussed: i) do air purifiers kill viruses, and ii) can a filter capture viruses?
Do air purifiers kill viruses?
Perhaps I should first stress the fact that viruses can be airborne, there is more and more evidence about this related to the Coronavirus as discussed in my separate text.
Now back to the question above, the short answer is no. But there is more to this. If an air purifier is equipped with a UV or more precisely UVC light source, then the air together with everything in it is exposed to this light which has harmful effects on viruses. They are not necessarily killed by the UVC light, but it makes them harmless. So it is almost as if they are killed.
You can read more about this in my separate text on how UVC air purifiers work. Examples of air purifiers with a UVC lamp are given here, and one more is shown in the picture:
It is important to know that this same UVC light is harmful to humans as well, so under no circumstances you should expose your body, and in particular eyes, to a UVC light source. This is why one must be careful when using air purifiers that have a UVC chamber.
There is still more about this. HEPA air purifiers are supposed to remove at least 99.97% of contaminants at 0.3 microns in size. The ability to capture such particles is called its efficiency. More about this is in my separate text about HEPA filter efficiency.
However, as you probably know, this 0.3-micron limit is far above the size of a virus. For example, the Coronavirus that is behind the COVID-19 pandemic is of the size slightly above 0.1 microns. You can see its actual photo obtained by an electronic microscope in my separate text. So it is supposed to pass through such a filter. But is this really so? Keep reading.
Can a HEPA filter capture viruses?
Long before the current Coronavirus pandemic, there were scientific studies on filters used for air purifiers. For example in the paper by Kim et al. Experimental study of nanoparticles penetration through commercial filter media, they used silver nanoparticles in the range 3 – 20 nm (0.003 – 0.02 microns) in order to define nanoparticle filtration.
As you realize, these particles are much smaller than the Coronavirus. They were able to count both upstream and downstream of the test filter to determine the nanoparticle penetration for each specific particle size. They detected 99.99% efficiency. One more recent study of the same effect you can see in this NASA report.
The results may sound counter-intuitive, but there is some physics behind all this. The reason for such efficient removal of nano-particles is that there are several effects taking place in a filter when air and small particles are forced to flow through it. They include:
- Inertial impaction.
These effects are graphically presented in the picture below, more about this all you can read here.
The second picture depicts something that is similar to Brownian motion in physics. This particularly applies to the smallest particles. The last picture shows the case when the particles are larger than the pores in the filter. In this case the filter behaves like a net.
The bottom line is the following. i) If an air purifier is equipped with a UVC light, it should make viruses harmless. ii) Although pores in modern HEPA and other filters may be larger than particles and viruses, such tiny pollutants can still be removed from the air. iii) Viruses may be in saliva droplets and these are much larger and they are easier to capture by a filter.
Having an air purifier at home probably does not mean you are fully protected, but it can definitely help to keep the air cleaner. We do our best to add texts here regularly, so bookmark this site and visit it again. Thank you for reading. Please use the comment box below in the case of questions or comments.