last updated 21 Aug 2021

Purifiers are designes to filter aerosols (tiny particles or droplets suspended in the air). See Personal Protection Equipment The best-case scenario for filters that actually do achieve the HEPA standard is to filter particles down to 0.3 microns at 99.97% efficiency. How they work:

From: Dale
This is an article on air purifiers. - Other reviews say you need an activated charcoal filter for smoke & smell not just a HIPPA filter. In any case filters need to be changed regularly, an ongoing expense. Some say they will remove the larger smoke particles but not the smoke odor. Some ionizers produce ozone which is it's self a problem. I haven't looked up our Lasko fans to see if there is any comment on ozone from from them. We haven't used the ionizer other than a few times and it does tend to produce more dust on surfaces. It's not clear to me that it would be worth it for the cabin given the need for regular cleaning and filter changes. Some comments said that use with a dirty filter can be worse than no air purifier.


Cnet Comments: According to multiple researchers they talked to, most consumer air purifiers simply don't have enough activated carbon to be an effective odor filter for more than a short period of time.
Instead of using a True HEPA filter, Blue Pure 121 uses a polypropylene fibers filter to help capture 99% of all allergens like dust, dust mites, pet dander, pollen and fungi (HEPA technology).
Ionic Air Purifiers vs HEPA filters.
While there are a number of different types of ionic purifiers, the most common are electrostatic precipitators and air ionizers. Ionic Air Purifiers create release negatively charged ions into your air, and bind to the dirty particles, causing them to become too heavy to float. They fall out of the air, and settle onto surfaces in your home or collect on walls and TV screens.
Many don't have fans so they are quiet but only cover a small area around them.
They also create ozone which is a pollutant but also is an oxidant with germicidal effects. Most immunologists say the irritating effects are not worth it.

Electrostatic precipitators use positively and negatively charged plates to collect dirt and dust particles as they pass through the machine. A fan pulls the pollutants towards the electrostatically charged plates, and collects them.
You just clean the plates periodically.

Most immunologists recommend (HEPA) filters . The ultra-fine mesh on these filters traps all sorts of irritants


Reviews:
Which air filter rating should you trust? IQ air

Ultrafine particles range from 0.1 microns all the way down to 0.003 particles – the tiniest that exist. Ultrafine particles are so small that, once inhaled, they move straight through the lung tissue and directly into the bloodstream.

High Efficiency Particulate Air (HEPA)
The best-case scenario for filters that actually do achieve the HEPA standard is to filter particles down to 0.3 microns at 99.97% efficiency.
HEPA filters work in mechanical air purifiers and are made with randomly arranged micro-glass fibers.
Some so-called HEPA filters are made of ordinary synthetic fibers. Synthetic fiber media is a far less dense structure and is much less efficient at trapping particles than media made of fiberglass or specialty synthetic fibers.

Clean Air Delivery Rate (CADR) ratings were developed by the Association of Home Appliance Manufacturers (AHAM) in the 1980s as a way for the general public to navigate the claims made by air purifiers.
The CADR rating system has many weaknesses that dramatically limit its usefulness.

IQAir HealthPro Series $800

Recommended Room Air Purifiers | Consumer Reports

Models with mechanical filters: This is the type that CR tests. Air purifiers with pleated filters use fans to force air through a dense web of fine fibers that trap particles. Filters with very fine mesh are HEPA filters—those certified to collect 99.97 percent of particles of a certain size (0.3 micrometers in diameter—smoke and paint pigments, for example)

Models with activated carbon filters: Rather than catch particles like mechanical filters, sorbent filters use activated carbon that can capture some odor-causing molecules from the air. They may also tackle some gases, but they’re not particularly effective against formaldehyde, ammonia, or nitrogen oxide. Because activated carbon filters don’t combat particles, many air purifiers will have both an activated carbon filter and a pleated filter for catching particles. Activated carbon gets saturated faster than a pleated filter, though, and requires replacement more frequently—every three months, as opposed to every six to 12 months for pleated filters.

Electronic air purifiers: Electrostatic precipitators and ionizers charge particles in the air so that they stick to plates on the machine or to nearby surfaces by a magnetic-like attraction. CR doesn’t typically test electronic air purifiers or recommend them, because they can produce ozone which is a health threat.
The plates in those with plates to capture the particles quickly become “loaded,” and the air purifier efficiency often decreases by even 50% in just a few months. Some are passed off as HEPA.

Scores 91-62
Rated primarily on Dust, Pollen and Smoke removal
91 Alen BreatheSmart 75i Pure $750.00
90 Samsung Cube Stack $1,400.00
88 Blueair Classic 605 $830.00
85 Blueair Blue Pure 211+ $300.00
 Pre-filter – The fabric pre-filter  can catch the large particles.
 This pre-filter is washable or vacuumable.
 Particle filter – Instead of using a True HEPA filter,
 Blue Pure 121 uses a polypropylene fibers filter to help capture 99% of all allergens like dust,
 dust mites, pet dander, pollen and fungi (HEPA technology).

Activated Carbon Filter – The Activated Carbon filter is added inside the Particle filter and effective against smoke, odors, gases and VOCs. 77 Blueair HealthProtect 7470i $640.00 77 Blueair Blue Pure 211+ Auto $340.00 76 Samsung Cube $700.00 74 Honeywell InSight HPA5300B $250.00


Bamboo Charcoal Air Purifying Bags:
Do Bamboo Charcoal Air Purifying Bags Work? 4 Best Bags + Reviews
Top 10 Charcoal Air Purifiers of 2022 - Best Reviews Guide I don't think they actually test them.

Links:
Home Air Quality
National Air Quality (Outdoor)
Air Quality Index (AQI) for Smoke
Air Quality Index (AQI) Measurement Benefits Of High Efficiency Filtration To Children With Asthma | UC Davis