UPTAKE OF GAS-PHASE ACETONE BY WATER SURFACES

The mass accommodation coefficient (alpha) for acetone on water has been measured as a function of temperature in the range 260-285 K. The experimental method employs a monodispersed train of fast-moving droplets (80-230 mum in diameter) in a low-pressure flow reactor. Droplet-trace gas interaction times are on the order of a few milliseconds. The mass accommodation coefficient has a negative temperature dependence and decreases from 0.066 to 0.013 over the above range. As with the previously studied alcohols, alpha can be expressed in terms of an observed Gibbs free energy as alpha/(1 - alpha) = exp(-DELTAG(double dagger)obs/RT), with DELTAH(obs) = -12.7 kcal/mol and DELTAS(obs) = -53.6 eu. The implications of these results for atmospheric chemistry are examined.