UV treatment and air quality in a pool facility

We investigated how UV treatment of indoor pool water affects the concentration of trihalomethanes (THMs) and chloramines (NCl₃) in the air above one therapy pool. One-hundred and sixty-two samples of tTHMs (sum of the four most common THMs in swimming facilities) and thirty-six samples of NCl₃ were collected simultaneously at poolside and in the extract channel in a room with one therapy pool for 2 days a week over a period of 5 weeks. When the UV lamp was on, the concentration of combined chlorine in the water decreased 58%, the concentration of tTHMs in the air increased 37%, and the concentration of NCl₃ in the air decreased 15%. Between 42% and 56% of the gases in the air are recirculated back into the poolroom along with the recycled air. The correlation between NCl₃ and THMs in the air was stronger when the UV treatment was on (r² = 0.963) compared to when the UV treatment was off (r² = 0.472). Using a linear mixed model, 30% of the variability in THMs was attributed to UV treatment. For NCl₃, the number of bathers was the most important predictor variable. UV treatment has a limited effect on airborne NCl₃ but increases the air concentration of tTHMs.