Long-term field measurements of charged and neutral clusters using Neutral cluster and Air Ion Spectrometer (NAIS)


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.