You do what you have to do. If I had lung issues or allergies I'd use a HEPA filter for sure. I like activated carbon filters. Less stench in the tunnel, behind old Diesels, driving past carrion, or near the Frito Lay factory.like I said, my asthma conditions deminish (less caughing, gags, eyes runnin, phlem, blockd upper airway).
Is that what U mean?