Effectiveness of Air Pollution Mitigation Systems: Transport, Transformation, and Control of Ozone in the Indoor Environment

Buildings are critical environments governing our collective exposure to air pollution and energy consumption. While there exist concerns regarding increases in building energy consumption due to indoor air interventions, improvements to the quality of air indoors can improve health, comfort, and productivity. Air cleaning technologies that can improve indoor air quality with minimal energy consumption have become ever more important. These technologies are utilized at various scales; from passive removal of pollutants in the air entering the indoor environment to active cleaning of air within the breathing zone. To better understand the effectiveness of active and passive ozone mitigation technologies at the building scale, a field campaign, chamber experiments, and a multi-zone mass balance model are used. Field measurements of ozone removal, CO2 exchange, and evapotranspiration (ET) were conducted on a rooftop above a big-box retail store housing a green roof and standard rooftop. Rooftop vegetation and substrate material were collected from the field site and evaluated in chamber experiments to better understand the uptake potential of rooftop surfaces. HVAC filter samples were also collected to understand the ozone removal potential and secondary VOC formation on green and standard filtration mediums. Finally, a multi-zone model is built to evaluate the effectiveness of various mitigation techniques on breathing zone concentrations and ozone exposure fractions. Ozone removal estimates to rooftop surfaces were found to be modest; if uptake at the rooftop is idealized, removal is transport limited and the overall impact to occupants indoors is near negligible. On HVAC filters studied, ozone removal ranged between 3.5 % ± 2.8 % to 14 % ± 2.8 %; subsequent modeling suggests that further increases in removal efficiencies to HVAC filters can substantially impact indoor concentrations, but the realized effectiveness is also dependent on HVAC duty cycle and run-time. Ozone removal to HVAC filters may also form secondary compounds; ozonolysis reaction products were measured downstream of loaded filters. Finally, this work shows that ozone removal methods applied at the room-scale must compete with other sinks in the indoor environment, where removal rates necessary to reach a threshold 50 % minimum effectiveness may be unrealistic for room-scale air cleaning technologies. Breathing zone air cleaning shows potential; clean air delivery rates necessary for effective breathing zone air cleaning are two orders of magnitude smaller than the room air cleaners but air cleaning technology applied at this scale still needs development