The filters can be upgraded to filter out smaller particles to lower the contaminant concentrations
Viruses in particular are 1/400th the thickness of a human hair and require extremely fine filters to catch them effectively. HEPA filters (used in surgical operating rooms) would be required to achieve effectiveness of 99%+ capture rate at 0.3 micron size range. These filters are very expensive (first cost and replacement costs), and unfortunately place a very large strain on the performance of the equipment. The standard commercial HVAC equipment is designed to operate like “drinking a soda through a standard straw”… but changing to HEPAs would be the equivalent of “changing that straw to a coffee straw”… the amount of flow through the filter will be drastically reduced which can lead to temperature issues, maintenance issues, operation issues, and increase utility costs.