If you go to the microCovid site  (Google will find it, but this site strips links), and put in an approximate scenario  (indoors, 10 people total, 3 feet apart, talking normally, etc., very approximate, but there's no setting for One Person is Yelling at a time) and select the Environment menu, one of the dropdowns is "Indoors with a HEPA filter (flow rate 5X room size per hour) [1/4th the risk]

I haven't researched the microcovid site, but it does seem as though we might want to pony up for an air filter.

Best,

Cally