Henry's Law Constants (HLC, Matm -1) were determined for the diastereomeric mixture of the nonylphenol isomer 4(3′,5′-dimethyl- 3′-heptyl)-phenol diastereomers (NP353(+) and NP353(-)), tertiary octylphenol (t-OP) and γ-hexachlorocyclohexane (γ-HCH) in artificial seawater over a temperature range 278-298K using a dynamic equilibrium system. Trace organic substances present in the gas phase were trapped by tandem XAD-2 cartridges and extracted with a soxhlet extractor. The extracts were derivatived with N,O-bis(trimethylsilyl)-trifluoroacetamide (BSTFA), and then analyzed with GC-MS in the selective ion mode. At 293K and in artificial seawater, HLC (Matm -1) were found to be equal to: NP353(+), HLC=(483±169); NP353(-), HLC=(551±193); t-OP, HLC=(400±140); γ-HCH, HLC=(876±307). The obtained data were used to derive the following Van't Hoff expressions: ln HLC (NP353(+))=8.73 (±0.95)×(1000/T) -23.61 (±3.30); ln HLC (NP353(-))=8.61 (±0.91)×(1000/T)-23.08 (±3.18); lnHLC (t-OP)=9.03 (±1.40)×(1000/T)-24.83 (±4.86); lnHLC (γ-HCH)=6.17 (±1.08)×(1000/T)-14.28 (±3.75). The derived enthalpies of solvation for NP353(+), NP353(-), t-OP and γ-HCH are -72.6±7.9, -71.6±7.6, -75.1±11.5 and -51.3±9.0kJmol -1, respectively. The HLC measurements of γ-HCH, which was used as reference substance, were in good agreement with literature values and its corresponding derived enthalpy of solvation agrees well to the previous values reported in the literature. A reassessment of the air/water gas exchange based on experimentally derived HLC was made for the nonylphenol (NP) in the Lower Hudson River estuary (New York/New Jersey, USA) that was previously reported by Van Ry. A net atmospheric deposition was calculated for the gas exchange of NP in the Lower Bay (Ff w=0.13), and it nearly reaches the condition of equilibrium in the Upper Bay (Ff w=0.46). © 2004 Elsevier Ltd. All rights reserved.