If we cannot rely upon HEPA ratings, then what should consumers look for if we want to take air purification seriously? Short of going out to purchase industrial air purification equipment that is purpose-made for applications like clean rooms, I don't know how to evaluate and purchase for a residential application. There are lots of pollen allergy patients who would be very happy if they could live in a PassivHaus that can be made practically airtight and pass all incoming air and circulating through an actually effective air purification system.