In October, students at the University of Illinois, Urbana-Champaign, held an intimate jazz concert at a bar downtown, with an audience of about 20 peers and faculty members — all of whom held digital passes indicating they’d recently tested negative for Covid-19. Two jazz ensembles performed, sometimes with masks and coverings for their instruments, and other times without.

Behind the scenes, mechanical engineering professor Ty Newell tinkered with the airflow, turning the exhaust and recirculation fans on and off at different points during the night. His students monitored for changes in the air quality, using a special instrument to measure the concentrations of carbon dioxide and fine particulate matter, both key to determining if a building is well ventilated.

CC0 Creative Commons, Pixabay

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Clean are can be achieve through dilution / ventilation and filtration.  The best is using both because you can save on energy bills.