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 Hyytiälä, Finland, during 2006–2007. Pools of neutral and charged clusters
seem to be present all the time below 3 nm. The total concentration of 1.8–3.0
nm clusters was ~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.