Phys. Chem. Chem. Phys.

The rate and extent of physical adsorption of methanol, acetone and formaldehyde on ice were measured as a function of concentration and temperature. The gas ice interaction was analysed by applying adsorption isotherms to determine temperature dependent Langmuir constants, K(T) and saturation surface coverage, N-max. At low coverage a partitioning constant K-#(T) was derived. The dependence of K-# on temperature is given by K-#(T) = 6.24 x 10(-12) exp(6178/T) cm for methanol and K-#(T) = 1.25 x 10(-10) exp(5575/T) cm for acetone. For formaldehyde a temperature independent expression, K-# = 0.7 cm was derived. From these data adsorption enthalpies DeltaH(ads) of (-46 +/- 7) and (-51 +/- 10) kJ mol(-1) were obtained for acetone and methanol, respectively. The results were used to calculate the equilibrium partitioning of these trace gases to ice surfaces under conditions relevant to the atmosphere