Determination of the Henry's law constants of low-volatility compounds via the measured air-phase transfer coefficients

• Published in: Water research (Oxford) Vol. 120; pp. 238 - 244
• Main Authors: Chao, Huan-Ping, Lee, Jiunn-Fwu, Chiou, Cary T.
• Format: Journal Article
• Language: English
• Published: England Elsevier Ltd 01.09.2017
• Subjects: Air-water partition coefficients; Chemical Phenomena; Gases; Henry's law constants; Low-volatility compounds; Pesticides; Two-film resistance theory; Vapor-phase transfer coefficients; Volatilization; Water; Water Purification; Low-volatility compounds; Henry's law constants; Vapor-phase transfer coefficients; Two-film resistance theory; Air-water partition coefficients
• ISSN: 0043-1354; 1879-2448
• DOI: 10.1016/j.watres.2017.04.074

Accurate Henry's law constants (H) are unavailable for the majority of organic pollutants, especially those having a low volatility. A novel kinetics-based experimental method is introduced to determine H for a wide range of low-H compounds. The method consists of measuring independently the water-to-air transfer coefficient (KL) and the associated air-phase transfer coefficient (kG) of a low-H chemical (solute) in water when KL ≅ kGH prevails according to the two-film theory. The kG for a solute is obtained via a developed gas-dynamic equation that relates kG to the solute molecular weight and the solute-vapor escaping efficiency (β) through a boundary air layer. The value of β is only a function of the in situ air turbulence level, independent of the chemical species. Thus, the required β for solutes can be estimated from the evaporative rates of pure volatile liquids under the same ambient setting. By relating the estimated kG with the measured KL of a low-H solute, the solute H is established. The H values of 45 low-H chemicals, including many complex pesticides, in the range of ∼10−7 to ∼10−3 have thus been determined. The accountability of the method is underscored by the consistency of the measured and credible literature H values for a number of the low-H compounds studied. [Display omitted] •A kinetic method is developed to measure the Henry's law constants (H) of low-H chemicals.•Solute volatilization coefficient (KL) and air-phase transfer coefficient (kG) are determined.•The kG of a chemical is estimated via a novel vapor-dynamic equation.•Coupling KL with kG enables H to be determined based on the two-film theory.