I'm working on a big air purifier update for you! It's taking time because I'm wading through each brand's catalog of units with names like "57PFO3X 2X-Plus," and trying to determine whether that'll fit their "B62a2P1 Max" filters or their more carbon-rich "UltraBLOCK BLEND 4c6 PRO Combo" filters better. Haha.

It's a bit mind-boggling, but worth it: my goal is to deliver a really clear list of air purifiers that are most effective for your health, all weird numbers and marketing aside.

I expect it'll be finished by next week, as long as brands get back to me with answers to my questions. In the meantime, here's what I'm looking for:

1. A high smoke CADR

Clean Air Delivery Rate (CADR) is the most important thing to look for, because it's a consistent number you can use side by side between air purifiers. It lets you rank units against each other, unlike "suggested room size," which is a marketing number, or CFM, which measures how much air the fan moves rather than how much air actually gets cleaned. Higher is better. It's a measure of how quickly an air purifier is able to actually pull particles out of the air, which usually means a strong fan paired with a filter that's well-positioned and sealed around the edges so air can't leak past it. Smoke is the smallest size range where filters struggle most, so a high smoke CADR is the most impressive number for particle removal.

2. A VOC filter filled with activated carbon pellets

This is what captures VOCs from the air, like cooking odors, new-building off-gassing, and smoke smells. The pellets are better at doing this than carbon cloth or deodorizing pads because they have so much more surface area to trap VOCs within. I'm impressed with how many brands are finally adding these to their units! Air purifiers have traditionally only focused on particle removal, which is what HEPA filters do. But in 2018, VOCs from household products officially became 50% of outdoor air pollution, sharing the space evenly with car exhaust particles. They're finally getting a little more of the attention they deserve. For this, focus on how many grams or pounds the filter has: more is better for VOC removal.

3. Do No Harm

Fancy tech is often added to air purifiers by brands trying to differentiate themselves in a crowded space. Sometimes that innovation is great! I'm genuinely impressed with some of the ideas that have evolved, like wool and plant-based filtration material, pet bed shaped purifiers, and others. But, sometimes it backfires: PCO technology in air purifiers actually create formaldehyde and acetaldehyde as byproducts of incomplete VOC breakdown, in some cases leaving the air with more of both than it started with. In terms of tech, stick with the basics (HEPA and carbon) until we know more.

I've also thoroughly updated the FAQ about air purifiers, if you want to do a deep dive on the above and learn much more. Here's a screenshot of one of the nicer looking images I added:

What air purifiers capture, by size

Particle

Gas

Bar shows size range

* Radon appears here only as its progeny, the solid decay products that deliver the dose. Radon gas itself is not captured by filtration, and it keeps producing progeny in the room, so source removal comes first. The two rows are the same element in two populations: fresh progeny form tiny unattached clusters, then stick to room aerosol to form the much larger attached fraction. HEPA removes the attached fraction well, which leaves proportionally more of the unattached fraction, and that one delivers more dose per unit. See my radon guide.

Bands mark which stage captures a pollutant first, not the only stage that can. A HEPA filter would capture pet hair too; the pre-filter simply reaches it first. The boundary between the HEPA and adsorbent bands is a matter of phase, not size: particles get filtered, gas molecules get adsorbed.

To sum up where I'm at

I've finished a re-review of the air purifier brands I previously had listed. A few have changed their filters for the worse, and some for the better! See the updated reviews here. I also added IQAir to the mix.

Now, I'm working through Levoit, Coway, Canopy, sans, Intellipure, AirOasis, Windmill, Dayette, and the Corsi-Rosenthal box: all requests I got from you through the Request Tracker. If you want to add others, please do!

Also, a shout out and sigh of relief for Air Doctor for being the only brand with air purifiers that go from 1000-5000 in order of increasing efficacy.

That's it! Have a great weekend!