Atmospheric ions and nucleation: A review of observations

This review is based on ca. 250 publications, from which 92 published data on the temporal and spatial variation of the concentration of small ions (<1.6nm in diameter) in the atmosphere, chemical composition, or formation and growth rates of sub-3nm ions. The small ions exist all the time in the atmosphere, and the average concentrations of positive and negative small ions are typically 200–2500 cm−3. However, concentrations up to 5000 cm−3 have been observed. The results are in agreement with observations of ion production rates in the atmosphere. Concentrations of small ions increased in the early morning hours due to night time inversion, which leads to accumulation of radon. We also summarised observations on the conversion of small ions to intermediate ions, which can act as embryos for new atmospheric aerosol particles. Those observations include the formation rates (J2[ion]) of 2-nm intermediate ions, growth rates (GR[ion]) of sub-3nm ions, and information on the chemical composition of the ions. Unfortunately, there were only a few studies which presented J2[ion] and GR[ion]. Based on the publications, the formation rates of 2-nm ions were 0–1.1 cm−3 s−1, while the total 2-nm particle formation rates varied between 0.001 and 60 cm−3 s−1. The ionmediated processes were observed to dominate when the total particle formation rates were small, and, accordingly the importance of ion-induced mechanisms decreased with increasing total 2-nm particle formation rates. Furthermore, small ions were observed to activate for growth earlier than neutral nanometer-sized particles and at lower saturation ratio of condensing vapours.Non peer reviewe

Aerosol particle formation events and analysis of high growth rates observed above a subarctic wetland-forest mosaic

An analysis of particle formation (PF) events over a subarctic mire in northern Sweden was performed, based on number size distributions of atmospheric aerosol particles (10-500 nm in diameter) and ions (0.4-40 nm in Tammet diameter). We present classification statistics for PF events from measurements covering the period July 2005- September 2006, with a break over the winter period. The PF event frequency peaked during the summer months, in contrast to other Scandinavian sites where the frequency is highest during spring and autumn. Our analysis concentrates on calculated growth rates and estimates of concentrations and production rates of condensing vapour, deduced from the growth rates and condensational sink calculations, using AIS and SMPS data. Particle formation events with high growth rates (up to 50 nm/h) occurred repeatedly. In these cases, the newly formed nucleation mode particles were often only present for periods of a few hours. On several occasions repeated particle formation events were observed within one day, with differences in onset time of a few hour. These high growth rates were only observed when the condensation sink was higher than 0.001 s-1

Aerosol particle formation events and analysis of high growth rates observed above a subarctic wetland-forest mosaic

An analysis of particle formation (PF) events over a subarctic mire in northern Swedenwas performed, based on number– size distributions of atmospheric aerosol particles (10–500 nm in diameter) and ions (0.4–40 nm in Tammet diameter). We present classification statistics for PF events from measurements covering the period July 2005–September 2006, with a break over the winter period. The PF event frequency peaked during the summer months, in contrast to other Scandinavian sites where the frequency is highest during spring and autumn. Our analysis includes calculated growth rates and estimates of concentrations and production rates of condensing vapour, deduced from the growth rates and condensational sink calculations, using AIS and SMPS data. Particle formation events with high growth rates (up to 50 nm h-1) occurred repeatedly. In these cases, the newly formed nucleation mode particles were often only present for periods of a few hours. On several occasions, repeated particle formation events were observed within 1 d, with differences in onset time of a few hours. These high growth rates were only observed when the condensation sink was higher than 0.001 s-1