You Should Read This - 2020-05-27
Take a moment to read this article in Science magazine about COVID19, aerosol transmission and masks. It's not a study. It's published as a "perspective", more a review of the current science and an argument about the implications of the data. The upshot is a strong argument for universal mask wearing as long as COVID19 remain prevalent in the population and we have no vaccines or effective treatments. The more specific assertions are these.
First, the authors argue that the accepted science about aerosol transmission of respiratory viruses (exhaled fluids that can hang for more than a few seconds in the air) is based on experiments from the 1930s and is simply outdated. Basically the conceptual distinction between big particles that fall rapidly to the ground because of gravity and aerosols that persist in the air is based on 80 year technology that simply couldn't detect a lot of very small particles. The authors argue that there is abundant evidence that COVID is spread this way, especially by asymptomatic or undiagnosed individuals. This is especially the case is indoors in areas with limited ventilation.
They further argue that six feet distance probably is not sufficient to ensure against contagion. The authors use an analog or perhaps better to say an illustrative comparison about cigarette smoke. If you're close enough that you can smell the tobacco smoke from someone smoking a cigarette you're probably close enough to be inhaling aerosolized COVID virus. If that's a correct comparison obviously six feet isn't remotely enough.