The answer is two! There are essentially two kinds of air pollution. That’s the principle behind why all we need is two filters.
For every particle—and I mean every particle—a HEPA filter is all you need. They’re nothing fancy. Do HEPAs capture dust mites? Pet dander? Asbestos? Bacteria? Mold? The answer is yes.
The other category of air pollutants is gases. This includes chemicals that usually come from indoors—things like formaldehyde coming from furniture, chemicals coming from cleaning products, and even chemicals coming from wrinkle-free “treated” clothes. It’s a little bit hard to track down every single gas that carbon can capture, but scientific studies have found that carbon also captures ozone, NO2, and SO2.
Click here to read more studies and Smart Air original tests on this topic: https://smartairfilters.com/en/blog/what-combination-of-air-filters-do-i-need-to-protect-against-everything/