Indoor HEPA Filtration Mitigates Adverse Cardiorespiratory Effects of Ozone Reaction Products

When ozone (O₃) enters indoor environments, a substantial portion reacts with indoor chemicals, producing ozone reaction products (ORPs) that have shown adverse cardiorespiratory effects. Some ORPs partition to PM_2.5 that can carry these species to the deep lung and may even enter the circulatory system. High-efficiency particulate air (HEPA) filtration has been shown to reduce indoor PM_2.5 levels and may decrease the amount of ORPs reaching the deep lung. We, hence, hypothesized that HEPA filtration could mitigate ORPs' cardiorespiratory health effects. We analyzed data from an intervention study with 84 participants, 50 receiving indoor HEPA filtration and 34 serving as controls. Each participant underwent two assessments of cardiorespiratory biomarkers. We measured personal exposures to PM_2.5, O₃, and O₃ loss (a proxy for ORPs exposure). Among participants without HEPA filtration, O₃ loss was significantly associated with adverse changes in biomarkers of systemic oxidative stress, vasoconstriction, thrombosis, airway inflammation, and pulmonary oxidative stress. In stark contrast, no significant adverse associations between O₃ loss and these biomarkers were observed in participants receiving HEPA filtration. These findings suggest that HEPA filtration, in addition to being effective in reducing PM_2.5 exposure, may be useful in mitigating the harmful health effects of ORPs exposure.