To understand the very first steps of atmospheric particle formation and growth, measurements at the size where atmospheric nucleation occurs are crucially needed. We present number size distributions of > 0.8 nm ions and > 1.8 nm particles measured with the Neutral cluster and Air Ion Spectrometer (NAIS) at a boreal forest site in Hyyatiala, Finland, during 2006-2007. Pools of neutral and charged clusters seem to be present all the time below 3 mn. The total concentration of 1.8-3.0 nm clusters was similar to 1000 cm(-3), ranging from 50 to 6000 cm(-3), whereas the concentrations of charged clusters in this size range remained below 50 cm(-3). On average, both neutral and charged clusters seem to have different diurnal cycles on particle formation event and non-event days. We also compared the NAIS-derived concentrations with those obtained from other concurrent air ion and particle instruments and found that the NAIS concentrations are in agreement with concentrations determined with these other instruments.