Chlorine disinfectants, such as sodium hypochlorite (NaClO) and trichloroisocyanuric acid (TCCA), are widely used in outdoor swimming pools. However, the effects of solar irradiation on the formation of disinfection byproducts (DBPs) in the presence of diverse organic precursors in outdoor pools remain poorly understood. This study systematically evaluated DBP formation in outdoor pool water disinfected with NaClO or TCCA under sunlight versus dark conditions. Solar irradiation markedly enhanced targeted DBP formation in actual pool water, with a greater increase for TCCA (75.9–104.2%) than for NaClO (49.1–60.1%). In simulated pool water, sunlight consistently elevated DBP yields across varying concentrations of body fluid analogues, chlorine doses, and light intensities. Notably, while TCCA produced fewer DBPs than NaClO in the dark, it generated comparable or higher concentrations under sunlight. Quenching and deoxygenation experiments indicated that photogenerated reactive species (e.g., OH·, Cl·, O( 3 P), O 3 ) significantly promote DBP formation under light, with a particularly pivotal role in the TCCA system. Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) further revealed that sunlight increased both the number and oxidation state of novel chlorinated DBPs. This increase corresponds to the light-enhanced conversion of precursor formulas, particularly larger, more saturated, and oxygen-rich molecular structures. These findings provide the first molecular-level evidence that sunlight not only elevates the abundance of known DBPs but also drives the formation of more diverse and oxidized species, highlighting the need to explicitly account for solar exposure in the risk assessment and management of outdoor pools. • Sunlight enhanced DBP formation in outdoor pools disinfected with TCCA or NaClO. • TCCA yields fewer DBPs than NaClO in dark but matches/exceeds it under sunlight. • Photogenerated reactive species critically drive sunlight-induced DBP formation. • FT-ICR MS showed sunlight increased novel Cl-DBP quantity and oxidation state. • Sunlight promoted conversion of larger, saturated, oxidized precursors.
Li et al. (Sun,) studied this question.