Aerosols are particles less than 50 micrometers in diameter. They can stay airborne for an extended period of time before settling on a surface or landing on a nearby person. Aerosols contain fewer infectious virus particles because of their small size. Scientists don’t yet know how many particles of SARS-CoV-2 — the virus that causes COVID-19 — are needed to infect someone. But breathing in large numbers of aerosols that have the virus in them could add up to an infectious droplet. You can think of aerosols as being similar to dandelion seed puffs that drift through the air. They gradually make their way to the ground, but can travel pretty far before they do. Environmental conditions, such as wind and temperature, affect how far they travel. Scientists estimate COVID-19 aerosols can stay in the air for up to a half hour, depending on the environment. If you are indoors and the room is not well ventilated, they may remain in the air longer. If you are outdoors, the aerosols scatter quickly and pose less risk to others.