A planes air is changed/recirculated about every 3 minutes. Most airliners are equipped with HEPA filters for the recirculated air, while 40-60% fresh is brought in. Air flow is ceiling to floor.
Seats, fold down trays, heads (restrooms), etc are not what I would call hygienic. The trays are loaded with fecal material. God knows what’s in the pouches. Having someone next to me sneeze/cough/fart will not be immediately filtered.