Dynamic behavior of gas-phase NCl3 and CO2 in indoor pool facilities

Abstract

The presence of gas-phase trichloramine (NCl3) in indoor swimming pool facilities is associated with adverse health outcomes among swimmers and other pool users, as well as degradation of pool infrastructure. Given their similarities in terms of volatility (i.e., Henry's law constant), the dynamic behaviors of NCl3 and carbon dioxide (CO2) in the air above indoor pools were postulated to be similar. Experiments were conducted to characterize and quantify the dynamic behavior of gas-phase NCl3 and CO2 in a mechanically ventilated swimming pool facility. The results of these time-course measurements allowed for examination of the effects of background water circulation and swimmer-induced mixing on the dynamics of both compounds in the air space above an indoor swimming pool. Measured gas-phase NCl3 concentrations exceeded the suggested guideline values of 300 μg/m3 or 500 μg/m3 during periods of heavy use. Measured gas-phase CO2 concentration followed a similar dynamic pattern as gas-phase NCl3; gas-phase CO2 concentrations often exceeded 1000 ppmv during swimming meets. Mass balance models for gas-phase NCl3 and CO2 were developed to relate the characteristics of the indoor pool environment to their dynamics. The results of these modeling efforts indicated that the similarity of CO2 transfer behavior to NCl3 may allow the use of CO2, which can be measured with low-cost infrared gas sensors, as a control parameter for NCl3. Moreover, the models that were developed to describe the dynamic behaviors of these volatile compounds may serve as tools for pool design, optimization of pool operations, and control of their mechanical ventilation systems.