Air quality in passenger aircraft

2 Aircraft cabin ventilation In early commercial jet aircraft, passenger cabins were ventilated with 100% outside air. In more recent jet aircraft, approximately 50% of the ventilation air is outside air and the remaining 50% is filtered recirculated cabinair. This development has allowed for fuel savings as well as a supposed improvement in the relative humidity of cabin air. With typical passenger densities in modern airline cabins employing partial recirculation of cabin air, however, carbon dioxide concentrations have been shown to exceed 1000 ppmv (parts-per-million by volume) in some sections of the cabin on some flights. This has raised the question of whether air quality and ventilation are acceptable in modern jet airliner cabins.