We don’t have enough data to precisely tell (thanks, Orange Bird for your tireless incompetence) but the concern is the identified superspreading events. Choir practice (
https://www.nature.com/articles/s41598-019-38808-z), funerals, subways, meat factories— these are enclosed spaces or events of close contact which would worsen aerosol transmission. Anecdotally there is some possible evidence: the R_0 is significantly higher in densely populated areas with public transportation vs densely populated areas without major public transport usage.
“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, meaning it is currently under peer review, researchers used a model to estimate that a person standing and speaking in a room could release up to 114 infectious doses per hour. The researchers predict that these aerosolized bits of saliva would easily infect other people if this happened in public indoor spaces like a bank, restaurant or pharmacy.
Another thing to consider is how easy these particles are to inhale. In a recent computer model study, researchers found that people would most likely inhale aerosols from another person that is talking and coughing while sitting less than 6 feet away.
While this seems bad, the actual process from exposure to infection is a complicated numbers game. Often, viral particles found in aerosols are damaged. A study looking at the flu virus found that only exhaled by a person are actually infectious. The coronavirus also starts to die off once it has left the body, remaining viable in the air for up to three hours. And of course, not every aerosol coming from an infected person will contain the coronavirus. There is a lot of chance involved.
Public health officials still don’t know whether direct contact, indirect contact through surfaces, or aerosols are the main pathway of transmission for the coronavirus. But everything experts like myself know about aerosols suggests that they could be a major pathway of transmission.
Overall, the evidence suggests that it is much more risky to be inside than outside. The reason is the lack of airflow. It takes between 15 minutes and three hours for an aerosol to be sucked outside by a ventilation system or float out an open window.”
Medscape explanation of aerosol transmission
3D model of a person coughing in an indoor environment