There was an assumption not too long ago and by many, especially health authorities, that SARS-CoV-2 could remain in the air for just a few minutes.
Gradually, research is extending that further, first to 3 hours, and now to at least 16 hours of the virus remaining suspended in the air whilst still being capable of infecting human cells.
This is obviously both a good and bad development. Bad in the sense that we were all misinformed and likely many have assumed to be safe when not, and good in the sense that at least we now know the upper end of the danger.
In theory, this new research could mean that someone coughs out the virus on a bus at 5pm, and some could breathe it in at 9am the next morning.
This helps to explain the prevalence of the virus in closed environments, especially those with circulating air which is poorly filtered.
Superspreading incidents seem mostly tied to these confined spaces, but also where there are circulating air currents, loud shouting and singing, such as choirs.
https://wwwnc.cdc.gov/eid/article/26/7/20-0764_article
https://www.latimes.com/world-nation/story/2020-03-29/coronavirus-choir-outbreak
It seems very important to get airflow through confined spaces (in through, and out), rather than circulating internally. Opening doors and windows as much as one comfortably can in buildings and vehicles should provide the best protection.
Study linked below :
https://www.medrxiv.org/content/10.1101/2020.04.13.20063784v1