Simultaneous measurements of the vertical distribution on Rn-222, Aitken nuclei and small ions have been carried out in southwest France, several hundred kilometers from the Atlantic Ocean, between ground level and 6000 m. These measurements demonstrate the importance of radon as a tracer characterizing the continental nature of an air mass. Every one of the measurements shows an increase in the concentration of radon at altitudes in excess of 3000 m. The radon does not appear to have originated in the European continental land mass. The concentrations of Aitken nuclei, small ions and radon show a sudden variation at the upper limit of the planetary boundary layer which is due, at least in part, to the geographic location of the site at which the measurements were made. With certain simplifying hypotheses, the mean size of atmospheric aerosols can be deduced from these measurements. Abstract Simultaneous measurements of the vertical distribution on Rn-222, Aitken nuclei and small ions have been carried out in southwest France, several hundred kilometers from the Atlantic Ocean, between ground level and 6000 m. These measurements demonstrate the importance of radon as a tracer characterizing the continental nature of an air mass. Every one of the measurements shows an increase in the concentration of radon at altitudes in excess of 3000 m. The radon does not appear to have originated in the European continental land mass. The concentrations of Aitken nuclei, small ions and radon show a sudden variation at the upper limit of the planetary boundary layer which is due, at least in part, to the geographic location of the site at which the measurements were made. With certain simplifying hypotheses, the mean size of atmospheric aerosols can be deduced from these measurements.