Features in air ions measured by an air ion spectrometer (AIS) at Dome C

Year: 2017

Authors: Chen X., Virkkula A., Kerminen V., Manninen E., Busetto M., Lanconelli C., Lupi A., Vitale v., Del Guasta M., Grigioni P., Väänänen R., Duplissy E., Petäjä T., Kulmala M.

Autors Affiliation: Univ Helsinki, Dept Phys, POB 64, Helsinki 00014, Finland; Finnish Meteorol Inst, Air Qual Res, POB 503, FIN-00101 Helsinki, Finland; CERN, CH-1211 Geneva, Switzerland; Italian Natl Res Council, Inst Atmospher Sci & Climate, I-40129 Bologna, Italy; CNR, INO, I-50019 Sesto Fiorentino, FI, Italy; ENEA, Lab Observat & Anal Earth & Climate, CR Casaccia, I-00123 Santa Maria Di Galeria, RM, Italy.

Abstract: An air ion spectrometer (AIS) was deployed for the first time at the Concordia station at Dome C (750-60 S, 123-230 E; 3220ma:s:l:), Antarctica during the period 22 December 2010-16 November 2011 for measuring the number size distribution of air ions. In this work, we present results obtained from this air ion data set together with aerosol particle and meteorological data. The main processes that modify the number size distribution of air ions during the measurement period at this high-altitude site included new particle formation (NPF, observed on 85 days), wind-induced ion formation (observed on 36 days), and ion production and loss associated with cloud/fog formation (observed on 2 days). For the subset of days when none of these processes seemed to operate, the concentrations of cluster ions (0.9-1.9 nm) exhibited a clear seasonality, with high concentrations in the warm months and low concentrations in the cold. Compared to event-free days, days with NPF were observed with higher cluster ion concentrations. A number of NPF events were observed with restricted growth below 10 nm, which were termed as suppressed NPF. There was another distinct feature, namely a simultaneous presence of two or three separate NPF and subsequent growth events, which were named as multi-mode NPF events. Growth rates (GRs) were determined using two methods: The appearance time method and the mode fitting method. The former method seemed to have advantages in characterizing NPF events with a fast GR, whereas the latter method is more suitable when the GR was slow. The formation rate of 2 nm positive ions (JC 2 ) was calculated for all the NPF events for which a GR in the 2-3 nm size range could be determined. On average, JC 2 was about 0.014 cm..3 s..1. The ion production in relation to cloud/fog formation in the size range of 8-42 nm seemed to be a unique feature at Dome C, which has not been reported elsewhere. These ions may, however, either be multiply charged particles but detected as singly charged in the AIS, or be produced inside the instrument, due to the breakage of cloud condensation nuclei (CCN), possibly related to the instrumental behaviour under the extremely cold condition. For the wind-induced ion formation, our observations suggest that the ions originated more likely from atmospheric nucleation of vapours released from the snow than from mechanical charging of shattered snow flakes and ice crystals.

Journal/Review: ATMOSPHERIC CHEMISTRY AND PHYSICS

Volume: 17 (22)      Pages from: 13783  to: 13800

More Information: This work received financial support from the Academy of Finland (project nos. 264375 and 264390), the NordForsk funded Nordic Centre of Excellence CRAICC (Cryosphere-atmosphere interactions in a changing Arctic climate, project no. 26060), and the Academy of Finland\’s Centre of Excellence Programme (Centre of Excellence in Atmospheric Science – From Molecular and Biological Processes to the Global Climate, project no. 272041). Funding for this research was also provided by Consiglio Nazionale delle Ricerche and PNRA (projects 2009/B.04 and 2010/A3.05). We appreciate the support of the IPEV/PNRA Project \”Routine Meteorological Observation at Station Concordia\”, www.climantartide.it with the radiosounding data set. Xuemeng Chen acknowledges the Doctoral Programme in Atmospheric Sciences (ATM-DP, University of Helsinki) for financial support. Valuable advice from Sander Mirme is sincerely appreciated.
KeyWords: atmospheric chemistry; cloud condensation nucleus; concentration (composition); fog; ion; particle size; size distribution; spectrometer, Antarctica; Concordia Station; Dome Concordia; East Antarctica
DOI: 10.5194/acp-17-13783-2017

Citations: 10
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