A Near-Explicit\nReaction Mechanism of Chlorine-Initiated\nLimonene: Implications for Health Risks Associated with the Concurrent\nUse of Cleaning Agents and Disinfectants

Limonene, a key volatile chemical product (VCP) commonly\nfound\nin personal care and cleaning agents, is emerging as a major indoor\nair pollutant. Recently, elevated levels of reactive chlorine species\nduring bleach cleaning and disinfection have been reported to increase\nindoor oxidative capacity. However, incomplete knowledge of the indoor\ntransformation of limonene, especially the missing chlorine chemistry,\nposes a barrier to evaluating the environmental implications associated\nwith the concurrent use of cleaning agents and disinfectants. Here,\nwe investigated the reaction mechanisms of chlorinated limonene peroxy\nradicals (Cl-lim-RO<sub>2</sub>•), key intermediates in determining\nthe chlorine chemistry of limonene, and toxicity of transformation\nproducts (TPs) using quantum chemical calculations and toxicology\nmodeling. The results indicate that Cl-lim-RO<sub>2</sub>•\nundergoes a concerted autoxidation process modulated by RO<sub>2</sub>• and alkoxy radicals (RO•), particularly emphasizing\nthe importance of RO• isomerization. Following this generalized\nautoxidation mechanism, Cl-lim-RO<sub>2</sub>• can produce\nlow-volatility precursors of secondary organic aerosols. Toxicological\nfindings further indicate that the majority of TPs exhibit increased\nrespiratory toxicity, mutagenicity, and eye/skin irritation compared\nto limonene, presenting an occupational hazard for indoor occupants.\nThe proposed near-explicit reaction mechanism of chlorine-initiated\nlimonene significantly enhances our current understanding of both\nRO<sub>2</sub>• and RO• chemistry while also highlighting\nthe health risks associated with the concurrent use of cleaning agents\nand disinfectants.