[neom]

"HEPA filters capture pollen, dirt, dust, moisture, bacteria (0.2-2.0 μm), virus (0.02-0.3 μm), and submicron liquid aerosol (0.02-0.5 μm).[8][9][10] Some microorganisms, for example, Aspergillus niger, Penicillium citrinum, Staphylococcus epidermidis, and Bacillus subtilis are captured by HEPA filters with photocatalytic oxidation (PCO). HEPA is also able to capture some viruses and bacteria which are ≤0.3 μm."

"Eleven particle-size-segregated samples were taken to investigate the particle-size distribution of perfluoroalkyl substances (PFASs) using two five stage impactors in parallel. ... Particle-size distribution varied between perfluorooctane sulfonate (PFOS) and other perfluoroalkyl sulfonates (PFSAs), perfluorooctane carboxylate (PFOA) and other perfluoroalkyl carboxylates (PFCAs) and n-methyl-perfluorooctanesulfonamido ethanol (MeFOSE). Whereas PFOA and MeFOSE were predominantly observed in smallest size fraction (<0.14 μm), maximum PFOS mass fractions were observed in the coarser size fractions between 1.38 and 3.81 μm."

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

https://www.sciencedirect.com/science/article/abs/pii/S00456...

[pdabbadabba]

For those uninterested in digesting these details, the upshot of this seems to be: Yes. HEPA filters should capture these.

Edit: Though perhaps inefficiently. See the replies below.

[DoingIsLearning]

Hold on, that is very much the opposite of my interpretation.

HEPA filters are typically designed with 0.3μm pores this is mostly a legacy of medical applications (i.e. to guarantee they catch bacteria).

Submicron performance (< 0.3μm) is kind of down to luck. You need the submicron particle to travel on a larger liquid particule for it to adhere to the filter lattice.

The PFAS is a group of substances, the article is specifically talking about 6:2 FTOH (one of many PFAS substances) that is found in carpets etc.

6:2 FTOH specifically is a sub-micron compound, from the GP article the closest particle to it is PFOA which is <0.14 μm. So unless your 6:2 FTOH compound is travelling on a moisture particle it is unlikely it would be filtered.

To answer GGP question, a high MERV rating filter will probably catch some of these compounds but not the totality. Open your windows frequently (if outside air pollution allows wherever you live) and make sure you understand what products you have in your house.

[tzs]

> You need the submicron particle to travel on a larger liquid particule for it to adhere to the filter lattice

That's what intuition would suggest, but intuition turns out to be wrong when dealing with filters for microscopic things. There are at least four mechanisms by which a filter can trap particles, three of which work on particles smaller than the pores [1].

Briefly:

1. Big particles don't fit between the fibers of the filter. Think fish in a fish net. This is called sieving.

2. Particles too small for sieving but heavier than the surrounding flow don't make the turns as well as the surrounding flow when the flow goes around the fibers. The particles can get embedded in the fibers. This mechanism is called inertial impaction.

3. The smallest might be too small to actually be affected much by the flow of the surrounding fluid through the filter. The move by diffusion, and many will randomly hit the fibers and get stuck.

4. Particles too big for diffusion but too light for inertial impaction still can run into fibers and get stuck. This is called interception.

The effectiveness of sieving, inertial impaction, and interception all follow S shaped curves that start out low for small particles, then at some point start rising, and then level out. The sieving curve's rise is almost vertical. The rise for inertial impaction is steep but not nearly as steep as it is for sieving. The curve for interception's rise is much more relaxed.

The effectiveness for diffusion goes the other way. Much more effective for very small particles, then above some size drops down and is low from then on.

When you put all these together, you get a curve that is effective at the small end, and at some point as size goes up effectiveness drops, reaching a minimum, and then rises again to reach high effectiveness for particles above some certain size.

There is also a fifth mechanism in some filters where electrostatic attraction between the fibers and the particles catches some particles.

[1] https://donaldsonaerospace-defense.com/library/files/documen...

[DoingIsLearning]

TIL, I can't edit or delete my comment by now. Hopefully your comment amends my misunderstanding.

[sooheon]

Please don't spread misinformation that is easily debunked by wikipedia: https://en.wikipedia.org/wiki/HEPA#Mechanism

HEPA is actually twice as efficient at removing <0.01 micron particles than 0.3 micron.

[pdabbadabba]

I don't claim to know one way or the other. I was basing my interpretation on GGP's quotation from Wikipedia, which seems to indicate that HEPA filters can capture down to 0.02 μm. I note now, however, that it then goes on to suggests that HEPA filters don't reliably capture some other categories of larger particles, which is consistent with your comment. Edited accordingly.