Singapore Airlines, great information on how their inflight, AC systems operate
In situations such as the present, there are all kinds of rash statements made about airline AC systems. Here is some good factual information. SIA aircraft cabin air filtration systems are equipped with High Efficiency Particulate Air (HEPA) filters, which are effective at filtering microscopic particles. These air filters have a similar performance to those used in hospital operating rooms. In addition, air flows in and out of the cabin on a continuous basis. That means that the cabin air is refreshed every 2 to 3 minutes (or 20-30 times hourly).