Can air purifiers really filter 99.97% of all particles in air?

[coriander123]

On boxing day I bought 2 air purifiers (high grade hepa and activated carbon filters) for my parents and myself to increase their health, and just want to confirm if it's true that air purifiers can really filter 99.97% of all airborne particles?

 

If so, does that mean they work as effectively as trees and plants in filtering the air?

 

Thanks!

 

[Dagl1]

I'm no expert on filters, but I am almost certain that any enclosed space with a HEPA filter will be much less polluted than a similar room filled with plants. I would be careful with interpreting %'s, especially when comparing those numbers with, for instance plants. 

A HEPA filter is a specialised piece of equipment, and as such will most likely do a much better job than a plant of the same size. But the surface area of a HEPA filter will be many more times that of a plant of similiar size, so in what way do you mean "effectively" in your question.

Does 1 HEPA filter, work as effectively as 1 plant, or do we compare surface area? Do you give different weights to different types of particles? Maybe plants filter larger or smaller things at different efficiencies, and some may be more dangerous for human health than others. Your question is too vague to answer in one go I think, it is also not clear how you plan to use them. Will your house be sealed and all fresh air will enter through a filter? In that case it will by definition be better than plants, cause you just cant put enough plants in between the source of new air and you/your parents.

On the other hand, one could, theoretically (and realistically it isn't that hard) create an environment that constantly recycles its own air by using plants, just need to make sure the O2 and CO2 production are in equilibrium around the optimal levels for human consumption. In that case you would only need small amounts of outside air to combat leakage etc. In that case I would assume the air in your eventually becomes cleaner than using a HEPA filter (assuming plants and the surrounding support-(micro)biome don't produce new airborne particles that are unhealthy etc). 

-Dagl

Edited January 5, 2020 by Dagl1
Typo

[John Cuthber]

Since plants don't really "filter" air...

[Strange]

I imagine they are much more effective than plants. There is some evidence that some plants (or, more likely, microbes in the soil) can remove some gases from the air. To some extent. But they probably won’t tackle particulates, which can be a greater health hazard. Especially if you are in an area with a lot of diesel traffic or wood/coal burning. 

[dimreepr]

I wondered if the definition of particle would come up...

Edited January 5, 2020 by dimreepr

[coriander123]

Thanks for all the replies everyone.

So my goal is to make the air in the house as close to perfectly clean as possible. Unfortunately we have 3 smokers in the house who smoke at least a half a pack a day, and was wondering if 2 air purifiers (one is a 1000 Philips purifier with a 200 sq foot capacity and another is the 2000 Philips purifier with 300 sq coverage) would be able to effectively remove close to 100% of all the particles from the smoking and everything else, as in everything else I mean any and every particle (from pollution, household products etc) in the air down to the smallest possible micron size. The air quality index where I live is an average of 20 so I'm not too worried about pollution, but very much so about the second hand smoke.

 

@Dagl1 Nope the house normally has at least 3 windows open during the winter for fresh air.

My ultimate question, and I apologize for not being clear enough, is does the 99.97% filtration efficiency the purifier claims to be able to perform at include every single impure particle in the air or does the 99.97% rate only include particles as small as a certain micronic size? I wasn't able to find this anywhere. Since the filters state they're only able to remove particles down to a size of 0.3 microns, but are there a plethora of other particles much smaller than that (for example from a lot of second hand smoke) that pass right through the filter that could otherwise be easily filtered by other means such as plants? They say the activated carbon filter somehow absorbs the cigarette smoke because of the massive amount of surface area carbon has, but I'm not sure what particles that are less than 0.3 microns that the filter isn't absorbing. Also it says the purifiers has a ultra fine particle removal of 20 nm, does cigarette smoke consist of ultra fine particles smaller than 20 nm that should be filters? and are there any other methods of air purification that can filter 1 nm particles or is that possible/necessary?

 

(edit) The purifier not only has a HEPA filter for removing dust, etc, but also an activated carbon filter which has the role of absorbing smoke and gas particles, and I'm not sure if the 20nm or 0.3 micron value applies to the carbon filter or to the HEPA filter or vice versa.

 

Much thanks

Edited January 6, 2020 by coriander123

[John Cuthber]

I realise it's probably impractical but, by far, the best way to reduce the contamination is to get the smokers to go outside.

No matter how good the purifier is, there will be particles "en route" to it which you will be stuck with inhaling.

To some degree, it's not a matter of how good the filter is, but how fast the fans can push air through that filter.

For example, if the fans only move 10 m³ per hour but  the room's natural ventilation is 100 m³ per hour, the filter isn't going to achieve as much as you would hope.

https://en.wikipedia.org/wiki/Air_changes_per_hour

[swansont]

The 99.97% is probably a measurement of input air vs output air (if it's legit), not of an entire enclosed space, and using a brand-new filter. If your air purifier is moving 10 m^3 of air per hour (to use the earlier example), but the room is 50 m^3, it's going to take a while to filter the air — the purer air will mix with the smoky air, so you'll see about a 20% reduction in one hour, with an exponential reduction in smoke particles. (this means ~8 hours to reasonably clean the room, not 5, assuming no source). A dirty filter is less efficient and that increases the time to reduce the smoke levels.

In addition to John Cuthber's point above about the introduction of new air, consider that smoke gets into a lot of materials, and will be a continual source of contaminants even after a smoker leaves/stops smoking.  

[Strange]

6 hours ago, coriander123 said:

My ultimate question, and I apologize for not being clear enough, is does the 99.97% filtration efficiency the purifier claims to be able to perform at include every single impure particle in the air or does the 99.97% rate only include particles as small as a certain micronic size? I wasn't able to find this anywhere. Since the filters state they're only able to remove particles down to a size of 0.3 microns, but are there a plethora of other particles much smaller than that (for example from a lot of second hand smoke) that pass right through the filter that could otherwise be easily filtered by other means such as plants?

Particulates are usually defined as PM10 (less than 10 microns), PM2.5 (less than 2.5 microns) and PM1 (less than 1 micron). Cigarette smoke contains particles in all these ranges. So it sounds as if your filters will catch most of these. There will, inevitably, be some particles smaller than this. And the filter will not get all thse within range, for the reasons stated. 

It is impossible to remove them all. Semiconductor manufacturing clean rooms spend millions on air purification but even at Class 1 (the highest standard) there will be some particulates ate 0.5 microns and below. This requires people entering to wear disposable coveralls ("bunny suits") and take an "air shower" before entering. And definitely no smoking.

It can't do any harm to add some plants, as well (as long as they are not toxic!). But I'm not sure it will have much benefit. Maybe you could get an air quality monitor and test the effectiveness?