Indoor air can include trace amounts of contaminants: e.g., dust, smoke, carbon monoxide, as well as volatile organic compounds generated or outgassed from the living space as a byproduct of our modern building methods. As indoor air flows through the return ducts of a heating, ventilation and air conditioning (HVAC) system, the air first encounters a system air filter which blocks the passage of particulate contaminants, and allows the return air to enter the portion of the HVAC system where it is heated, cooled, humidified, or dehumidified.
While filters are essential in removing particulate contaminants from the air prior to conditioning, they only block the passage of some particulate contaminants but do not destroy them. As a result, some air filtration and purification systems utilize ultraviolet (UV) radiation in combination with air filters in HVAC systems to further kill airborne bacteria and viruses. Photocatalytic oxidation (PCO) air purification systems employ a photocatalytic coating, such as titanium dioxide, inter alia, in combination with an activating photonic light source of a particular wavelength to destroy indoor airborne contaminants including volatile organic compounds such as formaldehyde, toluene, propanol, butene, and acetaldehyde. The system arrangement commonly includes one or more ultraviolet lamps, and a photocatalytic monolith, such as a honeycomb, coated with the photocatalytic coating. Titanium dioxide, e.g., is well known as a photocatalyst in a fluid purifier to destroy such contaminants.