Influence of Germicidal UV (222 nm) Lamps on Ozone, Ultrafine Particles, and Volatile Organic Compounds in Indoor Office Spaces

Germicidal ultraviolet lamps with a peak emission at 222 nm (GUV222) are gaining prominence as a safe and effective solution to reduce disease transmission in occupied indoor environments. While previous studies have reported O₃ production from GUV222, less is known about their impact on other indoor constituents affecting indoor air quality, especially in real occupied environments. In this study, the effects of GUV222 on the levels of ozone (O₃), ultrafine particles (UFPs), and volatile organic compounds (VOCs) were investigated across multiple offices with varying occupancies. O₃ from the GUV222 operation was observed to increase linearly (∼300 μg h^-1 m^-1) with a UV light path length from 0 to 3 m beyond which it stabilized. When applied in offices, the O₃ production models based on continuous measurements revealed O₃ production rates of 1040 ± 87 μg h^-1. The resulting increases in steady-state concentrations of 5-21 μg m^-3 were highly dependent on the number of office occupants. UFP production occurred during both unoccupied and occupied conditions but predominantly in newly renovated offices. Time-resolved measurements with a proton-transfer-reaction time-of-flight mass spectrometer (PTR-TOF-MS) revealed clear alterations in office VOC concentrations. Unsurprisingly, O₃ oxidation chemistry was observed, including monoterpene deprivation and 4-oxopentanal (4-OPA) production. But additionally, significant alterations from unidentified mechanisms occurred, causing increased levels of various PTR-TOF-MS signals including C₂H₅O₂⁺ and C₄H₉⁺ hypothesized to arise from photoinduced formation or off-gassing during the GUV222 lamp operation.