Measurements and Modeling of GUV222-Driven Increases in SOA Concentrations in an Unoccupied Office

The COVID-19 pandemic led to heightened interest in germicidal ultraviolet (GUV) lamps, which can deactivate bacteria and viruses in infectious aerosols. Recently, lamps using 222 nm (GUV222) light to disinfect occupied spaces have become more popular and available, as that wavelength is safer for human exposure compared to 254 nm lamps. However, GUV222 produces ozone, which drives the formation of other pollutants. Previous work in a controlled Teflon chamber with GUV222 has shown the production of ozone, followed by the formation of secondary organic aerosol (SOA) from limonene ozonolysis, and developed a model of this process. This work adapts that model to newly obtained measurements in an unoccupied office. The model is able to accurately predict SOA formation and yield given a continuous source of limonene, and we use it here to show how GUV222 lamps increase SOA exposure in indoor spaces. SOA yields from limonene in the office were found to be similar to those measured in a Teflon chamber. However, SOA formation resulting from briefly emitted limonene was harder to capture in the model. Typically, these limonene injections led to the formation of many ultrafine particles, which did not result in a significant increase in SOA mass, although they can still pose a risk to human health. GUV222 also had other impacts on room chemistry; concentrations of most VOCs increased under GUV222, potentially driven by gas and surface-phase ozone reactions as well as direct surface emissions.