Real-Time Measurements of Gas-Phase Trichloramine (NCl₃) in an Indoor Aquatic Center

Abstract

NCl3 is formed as a disinfection byproduct in chlorinated swimming pools and can partition between the liquid and gas phases. Exposure to gas-phase NCl3 has been linked to asthma and can irritate the eyes and respiratory airways, thereby affecting the health and athletic performance of swimmers. This study involved an investigation of the spatiotemporal dynamics of gas-phase NCl3 in an aquatic center during a collegiate swim meet. Real-time (up to 1 Hz) measurements of gas-phase NCl3 were made via a novel on-line derivatization cavity ring-down spectrometer and a proton transfer reaction time-of-flight mass spectrometer. Significant temporal variations in gas-phase NCl3 and CO2 concentrations were observed across varying time scales, from seconds to hours. Gas-phase NCl3 concentrations increased with the number of active swimmers due to swimming-enhanced liquid-to-gas transfer of NCl3, with peak concentrations between 116 and 226 ppb. Strong correlations between concentrations of gas-phase NCl3 with concentrations of CO2 and water (relative humidity) were found and attributed to similar features in their physical transport processes in pool air. A vertical gradient in gas-phase NCl3 concentrations was periodically observed above the water surface, demonstrating that swimmers can be exposed to elevated levels of NCl3 beyond those measured in the bulk air.

Elevated levels of chloramines and chlorine detected near an indoor sports complex

“…Subsequent surface disturbances in pool water, for example from swimming, have been shown to accelerate the transfer of produced chloraminespredominantly NCl 3to the gasphase. 10,11 Recent real-time measurements by Wu et al observed indoor NCl 3 levels increasing with the number of active swimmers, reaching peak concentrations up to 116 and 226 ppbv during swimming activities. 10 A median mixing ratio of 80 ppbv of NCl 3 was measured by Weng et al in an indoor swimming pool facility, despite a high outdoor to indoor air exchange rate (AER) of 9 h −1 .…”

“…10,11 Recent real-time measurements by Wu et al observed indoor NCl 3 levels increasing with the number of active swimmers, reaching peak concentrations up to 116 and 226 ppbv during swimming activities. 10 A median mixing ratio of 80 ppbv of NCl 3 was measured by Weng et al in an indoor swimming pool facility, despite a high outdoor to indoor air exchange rate (AER) of 9 h −1 . 12 The observed high levels of NCl 3 highlights how even with proper ventilation chloramines can reach levels that are hazardous to human health indoors (see below).…”

“…Taken together, indoor environments with elevated AER are likely direct sources of reactive chlorine species (i.e., Cl*) to the outdoor atmosphere. 6,10,[12][13][14][15][16] The need for high AER is because elevated levels of gas-phase chloramines in indoor areas are a health concern, with exposure linked to eye irritation, rashes, and respiratory difficulty. 17 The World Health Organization (WHO) recommends levels of gaseous chloramines (measured as NCl 3 ) to be below 90 ppbv; while a study by Parrat et al argues that this limit should be 60 ppbv.…”

Long-Term Monitoring of Water and Air Quality at an Indoor Pool Facility during Modifications of Water Treatment

“…Long-term investigations of gas-phase NCl 3 concentration in indoor chlorinated swimming pools have been conducted in recent years [17][18][19][20]. However, most of these previous investigations have incorporated analytical methods that were only able to report measurements every 30 min or more [21]. In this study, gas-phase NCl 3 is measured with a Next Environmental Monitoring (NEMo) Indoor Air Quality (IAQ) monitor (NEMo XT, Ethera Labs, Crolles, France), which reports measurements of gas-phase NCl 3 concentration every 10 min [22,23].…”

Comparison of sampling collection strategies for assessing airborne trichloramine levels in indoor swimming pools

“…The past thirty years have seen rapid advances in TCA exposure assessment, and several studies assessed TCA levels in indoor swimming pools using different sampling strategies (Soltermann et al, 2014;Zwiener and Schmalz, 2015;Wu et al, 2021). Modi ed Hery methods have been reported using different sampling pump ow rates and types of pre lters.…”