“NIAID virologist Vincent Munster and his colleagues used a nebulizer — a device that creates an aerosol from liquids — to release samples into the air of both the new coronavirus and the one that caused the SARS outbreak in the early 2000s. They reported detecting viable virus in aerosols for up to three hours. That compared to the four hours that active virus particles were found on copper, up to 24 hours on cardboard, and up to two or three days on plastic and stainless steel.
Both the Covid-19 and the SARS viruses had an aerosol half-life of 2.7 hours, meaning half the particles drop out of the air after that amount of time, and half of what remains drop out after another 2.7 hours. After a day, roughly nine half-lives, 0.002 (0.2 of 1%) of the original particles remain. As a result, the scientists said, “aerosol … transmission of [the new coronavirus] is plausible, as the virus can remain viable in aerosols for multiple hours.”’
Update: NEJM article on the results of testing environmental stability of novel coronavirus, and its persistence as an aerosol.