Particle number fluxes were measured by the eddy covariance method above a Scots pine forest in southern Finland. The observed number fluxes included particles with sizes down to 10 nm in diameter. The errors of measured particle number fluxes resulting from the technical limitations of particle counter and atmospheric fluctuations of water content are estimated. Simultaneous aerosol size distribution measurements were used to obtain information on particle sizes contributing to the flux. During new particle formation events the particle fluxes were dominated by nucleation mode particles, allowing the deduction of the deposition velocities characteristic to those particles. The corresponding deposition velocities were within a range from 5 to 40 mm s-1. ¿ 2000 American Geophysical Union