28 Jun 2022
28 Jun 2022
Status: this preprint is currently under review for the journal ACP.

Measurement Report: Increasing trend of atmospheric ion concentrations in the boreal forest

Juha Sulo1, Janne Lampilahti1, Xuemeng Chen2, Jenni Kontkanen1,3, Tuomo Nieminen1,4, Veli-Matti Kerminen1, Tuukka Petäjä1, Markku Kulmala1,5, and Katrianne Lehtipalo1,6 Juha Sulo et al.
  • 1Institute for Atmospheric and Earth System Research/Physics, University of Helsinki, 00014 Helsinki, Finland
  • 2Laboratory of Environmental Physics, University of Tartu, Tartu, Estonia
  • 3CSC - IT Center for Science Ltd., Espoo, Finland
  • 4Institute for Atmospheric and Earth System Research / Forest Sciences, Faculty of Agriculture and Forestry, University of Helsinki, 00014 Helsinki, Finland
  • 5Aerosol and Haze Laboratory, Beijing Advanced Innovation Center for Soft Matter Science and Engineering, Beijing University of Chemical Technology, Beijing, China
  • 6Finnish Meteorological Institute, 00560 Helsinki, Finland

Abstract. The concentration of atmospheric ions affects the total aerosol particle number concentrations in the atmosphere as well as atmospheric new particle formation via ion-induced nucleation, ion-ion recombination, and effects on condensational growth. In this study, we investigate the concentrations and long-term trends of atmospheric ions in a boreal forest environment using 16 years of cluster ion (0.8 – 2 nm) and intermediate ion (2 – 7 nm) measurements and characterize the most important factors that explain those trends. We found that the median concentration of cluster ions in a boreal forest was 710 cm-3, the median concentration of 2 – 4 intermediate ions was 14 cm-3 and the median concentration of 4 – 7 nm intermediate ions was 9 cm-3. The concentrations of both cluster and intermediate ions have been increasing over the 16- year measurement period, with cluster ion concentrations increasing by about 1 % per year and intermediate ion concentrations increasing 1.7 – 3.9 % a year. The increase in cluster-ion concentrations can be best explained by the decrease in the coagulation sink caused by larger aerosol particles. Meanwhile, the dependence of intermediate ion concentrations on meteorological conditions is evident, but ionization sources and the coagulation sink do not seem to explain the increasing trend. This is likely because the dynamics of intermediate ions are more complicated, so that ionization sources and coagulation sink alone cannot directly explain the variation. Season-specific analysis of the ion concentrations suggests that while coagulation sink is the limiting factor for the ion concentrations in spring and summer, the dynamics are different in autumn and winter. Based on our findings, we recommend that a more comprehensive analysis is needed to determine if the increase in ambient ion concentrations, increasing temperature and changing abundance of condensable vapors makes ion- mediated and ion-induced nucleation pathways in the boreal forest more relevant in the future.

Juha Sulo et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on acp-2022-392', Santtu Mikkonen, 06 Jul 2022
  • RC2: 'Comment on acp-2022-392', Anonymous Referee #2, 25 Jul 2022

Juha Sulo et al.

Data sets

smartSMEAR data Heikki Junninen, Antti Lauri, Petri Ilkka Rinaldo Keronen, Pasi Aalto, V Hiltunen, Pertti Hari, Markku Kulmala

Dataset from measurement report: Increasing trend of atmospheric ion concentrations in the boreal forest Sulo, Juha; Lampilahti, Janne; Chen, Xuemeng; Kontkanen, Jenni; Nieminen, Tuomo; Kerminen, Veli-Matti; Petäjä, Tuukka; Kulmala, Markku; Lehtipalo, Katrianne

Juha Sulo et al.


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Short summary
We measured atmospheric ion concentrations continuously in a boreal forest between 2005 and 2021 and observed an increasing inter-annual trend. The increase in cluster ion concentrations can be largely explained by overall decreasing level of anthropogenic aerosols in the boreal forest. This suggests that the role of ions in atmospheric new particle formation may be more important in the future.