The Interaction and Health Impacts between Ozone and Occupants Indoor: Observation and Model Simulation in a University Classroom

Ozone is a highly oxidative gas affecting human health, especially the impacts on the cardiovascular and respiratory systems. Ozone is usually formed through photochemical reactions outdoors and transported to the indoor environment. Occupants indoors might face an accumulated irritant issue due to high ozone reacting with human skin to produce several volatile organic compounds (VOCs), such as geranyl acetone (Ga), 6-methyl-5-hepten-2-one (6-MHO) and 4-oxopentanal (4-OPA), which might irritate skin and respiratory tract. In this study, the indoor air quality in a university classroom was monitored using air quality boxes (AQBs) comprising low-cost sensors for various gas species, including ozone, CO₂, NO_x, etc. The interaction processes between outdoor and indoor air, and human interference were investigated via a box model simulation of CO₂ and ozone temporal profiles. Both indoor CO₂ and ozone were significantly affected by the ventilation and number of occupants. CO₂ is primarily produced via human respiration and diluted via ventilation in the classroom, so the simulation of CO₂ profiles retrieves the ventilation efficiency and occupancy variation. With the derived parameters, ozone, mainly transported from the outdoors and consumed by room and human surface, is estimated to have deposition velocities of 0.028±0.0053 cm s^-1 and 0.45±0.15 cm s^-1 for room and human surface, respectively, consistent with the literature. The generation of Ga, 6-MHO, and 4-OPA depends on ozone consumption on human surfaces, and those VOCs might accumulate indoors for several ppb in a crowned room with poor ventilation. The integration of observation using low-cost sensors with the model simulation quantifies the physical and chemical processes controlling indoor ozone and organic ozonolysis. Furthermore, it might provide proper ventilation strategies to maintain good indoor air quality with energy efficiency based on the occupants.