How Ozone Dissolves in Pool Water: Henry's Law, Mass Transfer, and the Physics of Ozonation

Ozone's solubility in water is not unlimited or constant — it follows Henry's law, which relates the equilibrium concentration of a dissolved gas to its partial pressure above the liquid, with a temperature-dependent constant specific to each gas-water system. Foundational research establishing the Henry's law constant for the ozone-water system provided the quantitative basis engineers now use to calculate maximum achievable dissolved ozone concentration under given pressure and temperature conditions (ScienceDirect, "Henry's law constant for the ozone-water system"). This means dissolved ozone concentration has a physical ceiling that generator output alone cannot exceed — contact system design determines how close a system gets to that ceiling.

Much of the historical ozone research literature focused on ozone's reaction kinetics — how fast it destroys pathogens and oxidizes contaminants once dissolved. More recent research has pushed back on that framing, arguing that gas-liquid mass transfer, not reaction kinetics, is frequently the overlooked rate-limiting step in real ozone-based treatment systems (Environmental Science & Technology, ACS Publications, "Beyond Reaction Kinetics: The Overlooked Role of Gas–Liquid Mass Transfer in Ozone-Based Processes"). In practical terms, a system can generate more than enough ozone gas and still underperform if the contact chamber or injector fails to actually transfer that gas into solution efficiently.

Because mass transfer — not generation — is often the limiting factor, research has directly targeted improving the physical transfer process itself. A study examining whether ozone mass transfer in water treatment can be enhanced through independent pressurized ozonation found that operating the contact process under elevated pressure measurably improved dissolved ozone delivery, consistent with Henry's law's pressure-dependence (ScienceDirect, "Can ozone mass transfer in water treatment be enhanced through independent pressurized ozonation?"). A broader critical review of intensifying ozone gas/liquid mass transfer and ozonation efficiency surveys multiple engineering approaches — including injector design, contact chamber geometry, and bubble size control — confirming that mass-transfer intensification is now treated as its own dedicated engineering discipline within ozone system design (ScienceDirect, "Intensification of ozone gas/liquid mass transfer and ozonation efficiency: A critical review").

Because ozone transfer efficiency depends on the surface area and residence time available for gas-to-liquid transfer, injector and diffuser design — which controls bubble size — and contact chamber sizing — which controls residence time — are the practical levers system designers actually control. Research on ozone absorption in water specifically modeling mass transfer and solubility together demonstrates that these two variables interact: smaller bubbles and longer effective contact time both independently improve dissolved ozone yield for a given generator output (ResearchGate, "Ozone Absorption in Water: Mass Transfer and Solubility").

Because the physics of ozone dissolution — not generator capacity — sets the practical ceiling on treatment performance, correctly engineered pool ozone systems are designed around contact time, injection method, and pressure conditions calculated to approach the Henry's law solubility limit, rather than specified by generator output alone. This mass-transfer-first design approach is now the direction the ozone water-treatment research literature consistently points toward (Environmental Science & Technology, "Beyond Reaction Kinetics: The Overlooked Role of Gas–Liquid Mass Transfer in Ozone-Based Processes"; ScienceDirect, "Intensification of ozone gas/liquid mass transfer and ozonation efficiency: A critical review").