The Chemistry of Indoor Pools: Chlorine, Trichloramine, and a Paris Olympic Air-Stripping Solution

Overview

In this Science Friday episode Flora Lichtman chats with Purdue environmental engineer Dr. Ernest Blatchley about the chemistry inside swimming pools, focusing on how chlorine interacts with swimmer residues to form airborne byproducts that can affect health in indoor pools. The discussion also covers a successful air stripping approach used at the Paris Olympics to improve air quality around temporary indoor pools.

Key insights

• Pools behave as active chemistry reactors where chlorine reacts with organic matter left behind by swimmers.
• Trichloramine is a major volatile byproduct that contributes to the chlorine odor and can affect respiratory health.
• Air stripping, demonstrated at the Paris Olympics, can reduce the inhalation of harmful volatiles by removing them from water before they reach indoor air.
• Hygiene and swimmer habits, along with technological strategies like UV and optimized gutters, are part of the solution to manage indoor pool air quality.

Introduction: The pool as a chemistry reactor

The podcast introduces the idea that a swimming pool is not just a place for recreation but an active chemistry system. Dr. Ernest Blatchley explains that when people jump into a pool they leave traces on their skin and clothing, including sweat, deodorants, makeup, sunscreen, and even urine. The chlorine used to inactivate microbes does not simply stay inert; it reacts broadly with these materials, particularly with compounds containing organic nitrogen. These reactions produce a range of byproducts, some of which are volatile and can be inhaled or cause other health effects. The host, Flora Lichtman, emphasizes indoor pool air quality as a key concern for athletes and recreational swimmers alike.

Key chemical players: chlorine and chloramines

Chlorine is wired to inactivate pathogens, but its reactivity means it forms byproducts when it encounters organic matter. A sentinel group of compounds contains organic nitrogen, and among the reaction products trichloramine emerges as a notable volatile species. Trichloramine is responsible for the familiar chlorine odor at indoor pools and has known health impacts, particularly on respiratory systems. The discussion clarifies that not all chlorination byproducts are equally problematic; trichloramine is singled out due to its volatility and established health effects, while there are many other volatile chemicals present whose risks are less well defined.

Health implications: breathing, skin, and irritation

The podcast addresses how inhaling volatile byproducts like trichloramine can affect the lungs and airways, and how some individuals experience skin irritation from chloramines. The human sense of smell for these compounds varies widely, so relying on odor alone is not a reliable safety measure. The conversation also touches on outdoor pools where exposure dynamics differ because of ventilation, but indoor pools remain a priority because of accumulation of volatile compounds in enclosed spaces.

Engineering solutions: air stripping at the Paris Olympics

The centerpiece of the episode is the Paris Olympics field experiment. The Paris facility used an air stripping system to actively transfer volatile chemicals from water to the gas phase, then remove them outdoors before the air is breathed by swimmers and spectators. Blatchley describes the system as a short circuit around indoor air so contaminants exit directly to the exterior. The approach involved an intentionally deep gutter at the water’s edge, perforated pipes to generate fine bubbles in the water column, and a vacuum headspace to pull the volatile compounds out of the headspace. This configuration allowed the stripped air to be vented outside, reducing indoor concentrations of trichloramine and related compounds. The results were quantitatively favorable, demonstrating improved air quality in the indoor space comparable to traditional treatment outcomes in well managed facilities.

Alternative approaches and hygiene as a priority

While air stripping is effective, Blatchley stresses that reducing the presence of reactants is also crucial. This means focusing on swimmer hygiene to limit organic residues such as sweat, skin oils, and urine entering the water. The discussion notes UV treatment as a complementary approach to chlorine, offering a non-chlorine pathway to water treatment that can reduce the overall chlorine demand. The best strategy, according to Blatchley, combines improved swimmer practices with targeted technologies to minimize harmful byproducts while preserving disinfection efficiency.

Personal perspectives: swimming and health tradeoffs

Blatchley reflects on his 25 years of research, including his own experience with indoor pool environments. He discusses how better-managed pools have led to fewer respiratory symptoms in his current practice, reinforcing the real health impact of these engineering controls. The episode closes with an invitation to listeners to engage with the science of summer water quality and consider how pool design and user habits influence both safety and enjoyment.

Conclusion

In the final minutes, the guest and host emphasize the value of interdisciplinary solutions—environmental engineering, chemistry, and user behavior—to make pools safer and more comfortable for swimmers. The episode ends with credits and a note inviting listeners to share questions about pool science.