Certain aspects of the distribution of disinfection by-products (DBPs) in the air of indoor swimming pools, the exposure of the users, and possible health effects, have not been well documented. To determine the distribution of trihalomethanes (THMs), measurements were performed at 0.05 m, 0.60 m and 1.50 m above the water surface. These heights were chosen to measure the exposure in the breathing zone of the users. Air samples were collected from two indoor swimming pool facilities in Norway. Facility 1 uses calcium hypochlorite and facility 2 uses sodium hypochlorite for water treatment. In facility 2, one of the swimming pools is filled with 33% seawater, while the other pools in this study were filled with freshwater. Higher values were measured at 0.05 m compared to 1.50 m. Negligible differences between the measurements at 0.60 m and 1.50 m above floor levels were obtained. On average, 282% higher concentrations of total THM (tTHM) were measured in facility 2. Different disinfection products and ventilation concepts are possible explanations. Swimmers are exposed to higher concentrations compared to users by the poolside. For future studies, it is crucial to measure as close to the water surface as possible.

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