At University of Michigan – Ann Arbor, there is a study about the COVID-19 finished. It collected samples from air and surface at the public space to check the risk with different transmission way. The result shows that the risk of air transmission is 1000 times higher than the surface transmission. It is an addition study to our understanding of this infectious disease and mitigates efforts.
You can read the whole article by licking here.
Exposure Research Lab 