It sounds like there's increasing evidence that in indoor environments with sustained occupancy, aerosol transmission becomes significant for COVID-19. If so, it becomes useful not just to avoid such environments, but also to flush the air continuously as a precaution.
There's likely no feasible way to measure actual viral aerosol concentration, but I suspect that it would be correlated with CO2 levels across a certain range of ventilation strategies. CO2 is currently used in some HVAC systems as a proxy for air quality in general (other aerosols, VOCs, etc.), and CO2 monitors are relatively inexpensive. Would there be value in deploying CO2 monitors in grocery stores in order to confirm there are sufficient air changes per hour?