[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...