An apparatus and a method are provided for a heating, ventilation, and air conditioning (HVAC) system air filter for a building ventilation system. The HVAC system air filter comprises a supportive frame configured to orient the HVAC system air filter within the building ventilation system. A composite filter medium retained within the supportive frame comprises a cotton gauze portion and an electrostatic portion. The cotton gauze portion is configured for treatment with a filter oil composition to enhance airflow and filtration of air flowing through the composite filter medium. The electrostatic portion is configured to electrostatically attract and agglomerate airborne molecular contaminants and volatile organic compounds (VOCs) as small as 0.001 microns in diameter. In some embodiments, the composite filter medium comprises substances configured to release a fragrance into air passing through the composite filter medium.