I used to mow 1/2 acre of Bermuda grass at least once a week from May - October on a riding mower. Would take 2 1/2 hours. I used the n95's you get at Home Depot and would reuse them for many weeks and probably could have continued to reuse them until I couldn't breath through them or the straps broke. They're for stopping particulates so as long as they're not clogged they still work. If the particulates are infectious virus particles then reuse becomes more problematic but they still filter particles.