Indoor Illumination of Terpenes and Bleach Emissions Leads to Particle Formation and Growth

Application of chlorine bleach solution (major component sodium hypochlorite, NaOCl) in indoor environments leads to the emission of gaseous hypochlorous acid (HOCl) and chlorine (Cl 2 ), both of which are strong oxidants. In contrast to the outdoor atmosphere, where mixing ratios of HOCl and Cl 2 tend to be low (10s–100s of ppt), indoor HOCl and Cl 2 can reach high levels during cleaning activities (100s of ppb or higher). HOCl and Cl 2 may react with unsaturated organic compounds on indoor surfaces and in indoor air. In this study, we studied the reaction of limonene, one of the most common indoor volatile organic compounds (VOCs) arising from use of cleaning products, fragrance, and air fresheners, with HOCl and Cl 2 in an environmental chamber. A dark reaction was observed between limonene and HOCl/Cl 2 leading to gas-phase reaction products that were investigated using proton transfer reaction mass spectrometry (PTR-MS). With subsequent exposure to indoor fluorescent lights or diffuse sunlight through a nearby window, a substantial mass loading of secondary particles were formed with an averaged mass yield of 40% relative to the amount of limonene consumed. Aerosol mass spectrometry (AMS) measurements indicate a large contribution of particulate chlorine species. Electrospray ionization mass spectrometry (ESI-MS) analysis of filter-collected particles indicates the formation of high molecular weight products. This is the first study of the oxidation of limonene with HOCl and Cl 2, and it illustrates the potential for particle formation to occur with indoor lighting during the use of common cleaning products.