Simple.

B-Polar IonsFilters and UV would fall under the Reactive IAQ Technology. Air needs to carry contaminants to these technologies in order to be effective. Filters obviously capture some contaminants and UV needs to shed its light on airborne pathogens for at approximately 10-12 seconds which makes it great for keeping mold off coils but ineffective when treating air that is moving through air ducts where air is moving at around 16 feet per second.

Proactive technologies include increased ventilation which uses a mixture of outdoor fresh air brought into a classroom to dilute air that may contain airborne pathogens. Other technologies include bipolar ionization treating the air inside the supply ducts so that healthy ions enter the center of the classrooms inactivating airborne viruses while killing mold and bacteria. These technologies are a fraction of the cost of UV and have proven results. They also carry a very low maintenance cost. In fact, some of these technologies meet ASHRAE 62.1 IAQ and can actually decrease your energy costs.