Do Masks Help Part 4: Fluid Mechanics to the rescue

"Visualizing the effectiveness of face masks in obstructing respiratory jets" by Verna et al. reports on a simulation based on a manikin simulating coughs with a recreational smoke machine. Whether or not this should be considered an acceptable simulation of coughs is not something I can assess. The report looks at several scenarios: uncovered simulated coughs and simulated coughs through a variety of masks. While the results are quite striking, I believe they are answering the wrong question. Most of the arguments I've seen for wearing masks focus on reducing the spread from asymptomatic people,  especially in reducing the droplets spread through talking. I'd hope most people these days are considerate enough to cover their masks when the cough, so how well a mask stops the spread of droplets when the person coughs is not the question we should be seeking to answer.

The images from the paper are quite striking.  Contrasting the effects of a cough with no face mask

vs. a well-made home-built face mask

really demonstrates that if this set-up is a reasonable simulation of somebody coughing, masks can make a huge difference.  

But again, I think they are focused on answering the wrong question. Seeing what this would look like with normal exhalations, or a simulation of somebody speaking, would, I believe, do a better job answering the questions that should be answered. A measurement of environmental particulate matter after some time (say, an hour?) would also be a nice thing to see regarding how much masks help in office environments.