A simple theoretical model, based on the assumption that radon is transported by molecular diffusion combined with advective flow induced by barometric pressure, is used to investigate radon exhalation at three subsurface monitoring sites in the volcanic island of Tenerife, Canary Islands. The model is intended to filter out all known contributions to radon flux, in an attempt to find potential precursory signals of seismic and/or volcanic activity. For the period of observations (1 December 2000 to 1 April 2001), variations on radon concentration predicted by the model were in good agreement with those measured, confirming they were induced by atmospheric pressure changes.