The uptake of nopinone by liquid water at room temperature has been studied in a wetted-wall reactor coupled to a chemical ionization mass spectrometer and was found to be reversible and bulk-specific. A Henry's law constant of H(296¿3 K)=(175¿50) Matm-1 was obtained. Measuring the solubility using a bubble column technique resulted in a value of H(296¿1 K)=(200¿40) Matm-1. We recommend an average value of H(296¿2 K)=(195¿60) Matm-1. The temperature dependence of this coefficient has been measured between 274 and 298 K and corresponds to an enthalpy of solvation of ΔsolnH=-(98¿30) kJ/mol. The Henry's law coefficients measured in this work are large enough that, in the presence of clouds, aqueous-phase sinks of nopinone might compete with its gas-phase sinks. The possibility of such competition for other organic compounds in the atmosphere is discussed. ¿ 2001 American Geophysical Union