Effects of 222 nm Germicidal Ultraviolet Light on Aerosol and VOC Formation from Limonene

Abstract

Since the 1930s, germicidal ultraviolet (GUV) irradiation has been used indoors to prevent the transmission of airborne diseases, such as tuberculosis and measles. Recently, it has received renewed attention due to the COVID-19 pandemic. While GUV radiation has been shown to be effective in inactivating airborne bacteria and viruses, few studies on the impact of GUV on indoor air quality have been published. In this work, we evaluate the effects of GUV222 (GUV at 222 nm) on the chemistry of a common indoor volatile organic compound (VOC), limonene. We found that the production of O₃ by the GUV222 lamps caused the formation of particulate matter (PM) and oxygenated volatile organic compounds (VOCs). We also found that the chemistry proceeds through the ozonolysis of limonene as well as the reaction with secondary OH, and that the presence of GUV light led to observable but small perturbations to this chemistry. Understanding the effects of GUV222 on indoor air quality is important in evaluating the safety of these devices.

Figure 1

Modeled and experimental time series of limonene, ozone, SOA mass concentration, and SOA mass yield for an experiment under dry conditions.

Figure 2

Time series of limonene (LIM) reacting with O₃ measured by the PTR-TOF under dry conditions, similar to Figure 1, but now in units of molecules cm^–3 (A); the modeled and experimental loss rate of limonene and the modeled loss rate of limonene due to only O₃ (B) per eq 2); and modeled and experimental k_LIM+OH[OH] / k_LIM+O3[O₃] (C) per eq 3.

Figure 3

Experimental and modeled SOA produced from the oxidation of limonene (A), the experimental and modeled SOA formation rate (B), and the ratio of the modeled SOA to the experimental SOA formation rates (C) under dry conditions; gas-phase products produced from the oxidation of limonene (D), and the gas-phase products formation rates (E) under dry conditions.

Figure 4

Average signal (A) and the average formation rate (B) of gas-phase products during period c (lamp on) divided by the average formation rates during periods b and d (lamp off) as a function of m/z.