Virus-free air above the clouds
HEPA stands for "high efficiency particulate air filters." The air on planes consists of both fresh outside air that has been pulled in and scrubbed air that has been run through these high-tech, highly efficient filters. The systems can remove particles down to the size of 0.1 micrometers – a thousandth of a millimeter. This means they scrub the air of 99.9 percent of all viruses, bacteria and aerosols. These are the same filters that are used in operating rooms in hospitals.
HEPA filters were first developed for military use, to remove micro radioactive contaminants from the air. In the 1990s, they came into use in civil aviation, and now they feature on all Airbus aircraft.
Good ventilation stops viruses from spreading
Alongside this, the aircraft use a ventilation system that pumps a stream of fresh, purified air into the cabin throughout the flight. The air flows in through openings by the top luggage compartments and then leaves the cabin through exits by the floor. This vertical air flow means viruses cannot spread horizontally through the seats.
Using this system, the air in the cabin is completely renewed every three minutes – a far better ventilation rate than in many buildings. To address the current pandemic, these systems have also been modified to remain active any time there are passengers on board, including while the aircraft is grounded.