According to this it's a mixture of filtered recirculated air and outside air. I'll go with that. It's not a huge deal to me anyway because I don't fly anymore.
https://www.travelandleisure.com/tra...-during-flightThe number of these ventilation zones varies depending on the aircraft, but each zone typically goes through this filtration process 15 to 30 times within the hour, with 50 percent of the air getting re-circulated and 50 percent of the air coming from outside, according to Gendreau.