On Apr. 24, 2020, Shelly Miller, Professor of Mechanical and Environmental Engineering, University of Colorado Boulder, reported that the new coronavirus, SARS-CoV-2, is tiny, about 0.1 microns – roughly 4 millionths of an inch – in diameter. Aerosols produced by people when they breathe, talk and cough are generally between about 0.7 microns to around 10 microns ﾖ completely invisible to the naked eye and easily able to float in air.

Researchers don’t yet know how many individual pieces of SARS-CoV-2 an aerosol produced by an infected person’s cough might hold. But in one preprint study researchers used a model to estimate that a person standing and speaking in a room could release up to 114 infectious doses per hour. Public health officials still donﾒt know whether direct contact, indirect contact through surfaces, or aerosols are the main pathway of transmission for the coronavirus.