Indoor air quality can be improved by monitoring, with at least one air quality sensor, at least one air quality factor of a target environment. Then, based on the collected air quality factor, a HVAC system or an air purification system can be adjusted in order to more efficiently maintain the indoor air quality. Systems that may be used to improve indoor air quality can contain a photo-catalytic oxidation-based air purification system and can communicate with at least one air quality sensor, other purification systems, HVAC system controllers, or a computer configured to monitor and control the air purification systems and HVAC systems.