Scientists say the virus breathed or coughed can linger for 3 hours in the air. But that is tested in a lab of still air. Instead, remember pictures of old steam trains leaving a long cloud of smoke behind them that hangs along the track. The same thing would describe a person walking, a long trail of viruses in and invisible cloud that can hang in the air for several hours. 20 minutes of walking leaves a trail a mile long, not counting wind, which would keep the viruses floating longer and farther. If another person walks across the cloud several hours later after the person is long gone, they can breathe in the viruses. Good idea to wear masks if a local infection is known in the area, because anyone can be producing for days before showing systems.