Monochloramine, dichloramine and trichloramine (NH 2 Cl, NHCl 2 , NCl 3 ) are measured in the ambient atmosphere, in downtown Toronto in summer (median 39, 15 and 2.8 ppt) and winter (median 11, 7.3 and 0.7 ppt). NCl 3 and NHCl 2 were also measured in summer (median 1.3 and 14 ppt) from a suburban Toronto location. Measurements at two locations demonstrate prevalence of chloramines in an urban atmosphere. At both sites, NCl 3 exhibits a strong diel pattern with maximum values during the night, and photolytic loss with sunrise. At the downtown site, a strong positive correlation between NH 2 Cl and NHCl 2 in the summer night indicates a common source, with daily average peak mixing ratios approaching 500 and 250 ppt, respectively. As a previously unidentified source of chlorine (Cl) atoms, we demonstrate that NCl 3 photolysis contributes 49 to 82% of the total local summertime Cl production rate at different times during the day with an average noontime peak of 3.8 × 10 5 atoms/cm 3 /s, with smaller contributions from ClNO 2 and Cl 2 . Photolysis of NH 2 Cl and NHCl 2 may augment this Cl production rate. Our measurements also demonstrate a daytime enhancement of chloroacetone in both the summer and winter, demonstrating the importance of Cl photochemistry. The results suggest that chloramines are an important source of Cl atoms in urban areas, with potential impacts on the abundance of organic compounds, ozone, nitrogen oxides, and particulate matter. Future studies should explore the vertical gradients of chloramines and their contribution to Cl production throughout the boundary layer.

Per‐ and polyfluoroalkyl substances are a class of fluorochemicals that can degrade into perfluoroalkyl acids, which are well known to be persistent in the environment. It is thus important that novel fluorinated surfactants be designed to degrade into small, nonbioaccumulative products. We report the biotransformation and elimination kinetics of one such novel polyfluorinated surfactant, di(polyfluoroether thioether(S)‐oate) sulfonate (diFESOS), and its metabolites. Biotransformation was investigated in vitro using S9 liver fractions and in vivo in Sprague–Dawley rats. Rats dosed by oral gavage with diFESOS were found to have relatively fast elimination kinetics, with half‐lives on the order of hours, compared with legacy fluorinated surfactants such as the disubstituted polyfluoroalkyl phosphates that have half‐lives on the order of days. To interrogate degradation of the polyfluorinated chain, rats were then dosed with a polyfluoroether thioether alcohol (a suspected product of carboxylate cleavage of diFESOS) either orally or intravenously, and the novel metabolite 2H‐3:2 polyfluoroether sulfonic acid (2H‐3:2 PFESA) was identified. Perfluoropropionic acid was detected in rat urine and is likely a terminal product. The blood of orally dosed rats contained higher levels of metabolites than the blood of intravenously dosed rats, suggesting the importance of metabolism in the gut and liver. Elimination kinetics of all the novel metabolites were faster than their fully fluorinated counterparts. Environ Toxicol Chem 2021;40:3328–3336. © 2021 SETAC