[b_b]

I'd recommend anyone who would like to clean the air of the home to use products from SmartAir [1] which is as inexpensive as just a fan attached to a filter, both of which they sell (although you can just buy the filter by itself and attach it to a fan you already own). I visited their office in China and received a complementary filter, which when installed in my hotel room in Beijing, definitely cleared the air and there was a noticeable difference from such a simple mechanism. Recommended for both price and effectiveness.

[1] = https://smartairfilters.com/cn/en/?r=global

[sberder]

I wouldn't, I've used their filters and followed them from the very beginning. It is an inexpensive solution but comes with its own serious flaws. They're very noisy which doesn't really work well in rooms where you actually live. They also suffer from poor CADR (Clean Air Delivery Rate) as those fans were never designed to handle high pressure differentials (before/after filter) unless you run them at full speed which is noisy.

The project is interesting nonetheless, it helped demystifying purifiers and rectify the market prices in China (with other brands like Phillips and Xiaomi). Their new product for professional spaces is quite good.

[staikken]

I've worked for a company that measures PM2.5 in the past. Using a HEPA filter to remove PM2.5 seems unlikely to me. Perhaps there's something more going on here than I've picked up from a quick skim of the site (perhaps there's some sort of cyclonic separation happening) but I'm skeptical this is actually removing particulate at that scale.

[sberder]

I'm not sure I get what you're saying here, HEPA is a standard that was developed for medical environments & clean rooms [1]. To qualify as HEPA, a filter should be able to remove 99.97% of particles 0.3µm and above so it is definitely impacting PM2.5 (particles 2.5µm and below).

See my other comment [2] for my opinion on smartair solutions.

[1] https://en.wikipedia.org/wiki/HEPA [2] https://news.ycombinator.com/item?id=17720802

[staikken]

I was under the impression that the filtration efficiency by particle size for such a filter was not a linear relationship.[0] So manufacturing to a lower bound of 3 may not say much for particles even slightly smaller. My estimation of the magnitude of this effect may be off however as this company seems to suggest.

[0]https://www.globalspec.com/learnmore/manufacturing_process_e...

[clumsysmurf]

Correct me if I'm wrong, but the fans in these units appear to be axial — but ideally you would want centrifugal fans for this application.