Articles | Volume 16, issue 4
Atmos. Chem. Phys., 16, 1919–1935, 2016
Atmos. Chem. Phys., 16, 1919–1935, 2016

Research article 19 Feb 2016

Research article | 19 Feb 2016

High concentrations of sub-3nm clusters and frequent new particle formation observed in the Po Valley, Italy, during the PEGASOS 2012 campaign

Jenni Kontkanen1, Emma Järvinen1,2, Hanna E. Manninen1, Katrianne Lehtipalo1,3, Juha Kangasluoma1, Stefano Decesari4, Gian Paolo Gobbi5, Ari Laaksonen6,7, Tuukka Petäjä1, and Markku Kulmala1 Jenni Kontkanen et al.
  • 1Department of Physics, 00014 University of Helsinki, Helsinki, Finland
  • 2Institute for Meteorology and Climate Research, Karlsruhe Institute of Technology, 76021 Karlsruhe, Germany
  • 3Paul Scherrer Institute, 5232 Villigen, Switzerland
  • 4Istituto di Scienze dell'Atmosfera e del Clima, CNR, 40129 Bologna, Italy
  • 5Institute of Atmospheric Sciences and Climate, CNR, 00133 Rome, Italy
  • 6Department of Applied Physics, University of Eastern Finland, 70211 Kuopio, Finland
  • 7Finnish Meteorological Institute, 00101 Helsinki, Finland

Abstract. The concentrations of neutral and charged sub-3nm clusters and their connection to new particle formation (NPF) were investigated during the PEGASOS campaign (7 June–9 July 2012) at the San Pietro Capofiume measurement station in the Po Valley, Italy. Continuous high concentrations of sub-3nm clusters were detected during the measurement period, although the condensation sink was relatively high (median value 1.1 × 10−2 s−1). The median cluster concentrations were 2140 and 7980 cm−3 in the size bins of 1.5–1.8 and 1.8–3 nm, and the majority of them were electrically neutral. NPF events were observed during the measurement period frequently, on 86 % of the days. The median growth rates of clusters during the events were 4.3, 6.0 and 7.2 nm h−1 in the size ranges of 1.5–3, 3–7 and 7–20 nm. The median formation rate of 1.6 nm clusters was high, 45 cm−3 s−1, and it exceeded the median formation rate of 2 nm clusters by 1 order of magnitude. The ion-induced nucleation fraction was low; the median values were 0.7 % at 1.6 nm and 3.0 % at 2 nm. On NPF event days the neutral cluster concentration had a maximum around 09:00 (local winter time), which was absent on a non-event day. The increase in the cluster concentrations in the morning coincided with the increase in the boundary layer height. At the same time radiation, temperature and SO2 concentration increased, and RH and condensation sink decreased. The concentrations of neutral and charged clusters were observed to have a positive correlation with sulfuric acid proxy, indicating the significance of sulfuric acid for the cluster formation in San Pietro Capofiume. The condensation sink had a negative correlation with the concentration of charged clusters but no clear relation to the neutral cluster concentration. This finding, together with back-trajectory analysis, suggests that the precursor vapors of the clusters and background aerosol particles, acting as their sink, have possibly originated from the same sources, including e.g., power plants and industrial areas in the Po Valley.

Final-revised paper