Balancing discrete indoor air quality metrics: A chemical modeling study of the response of indoor air quality to airborne pathogen control strategies

The impact of airborne pathogen mitigation strategies on indoor air quality (IAQ) depends on the concentration of outdoor air pollutants, the emission and generation of indoor pollutants, and baseline ventilation conditions. Typical engineering solutions to reduce airborne pathogens include enhanced ventilation, in-room filtration, and germicidal UV radiation. Predicting the response of IAQ to these reduction strategies is challenging due to the wide variability in outdoor and indoor air pollutants and numerous configurations for engineered solutions. We use an existing, observationally constrained, open-access photochemical model to assess the response of IAQ metrics to actionable risk reduction strategies in mechanically ventilated buildings. We confirm two commonly held priors: 1) in-room filtration universally reduces PM2.5, while enhancing ventilation rates can increase PM2.5 depending on the quality of the HVAC intake filter and the concentration and size distribution of outdoor aerosol and 2) enhanced ventilation is the only strategy that reduces the indoor concentration of CO2 and indoor sourced VOC, but often at the expense of O3 and PM2.5. Uniquely, the model predicts the balance of O3, and aerosol production driven by the infiltration of outdoor air and photochemically driven indoor air chemistry, where chemical processes are less intuitive. We show that the response of commonly measured proxies for IAQ (e.g., CO2) do not always coincide with an overall improvement in indoor air quality.