Clean, fresh air is a concept many of us are familiar with. Think of the relief when someone pops open a window after you've been pushed up against strangers on a crowded public bus on a hot, sweltering day...or the way smoke clears with the help of a hood fan when something accidentally burns on the stove.
Since we now know that Covid is airborne and spreads like smoke (source), spending time indoors with others means we face a greater chance of inhaling Covid because it hangs in the air, even if a contagious person left. Thus, air ventilation and filtration aid us in achieving safer air!
To achieve lower numbers of contagious particles in spaces, we use air purification methods, such as HVAC systems, HEPA filters, Far UVC lights, opening doors and windows, or turning on a fan to create a cross breeze.
The level of air dilution is measured in air changes per hour (ACH). The Canadian Standard CSA Z 317.2 for air purification in health settings matches the US ASNI/ASHRAE standard guidelines, which settles on minimum 6 changes. The higher the number of ACH, the lower the level of CO2, pathogens, pollutants, mold, and bacteria!
We strive to follow the standard guidelines of at least 6 ACH, although this can vary sometimes depending on the venue, amount of people in attendance and the state of the building's HVAC system. That's where HEPA (high efficiency particulate air) & MERV13 (minimum efficiency reporting value) filters come in. HEPA filters clean the air AND trap virus particles (source). MERV13 filters (normally used in HVAC systems!) can even be used to make DIY CR boxes (an air purifier consisting of MERV13 filters duct taped to a box fan) (source).