Features in air ions measured by an Air Ion Spectrometer (AIS) at Dome C
Xuemeng Chen1, Aki Virkkula1,2, Veli-Matti Kerminen1, Hanna E. Manninen1,3, Maurizio Busetto4, Christian Lanconelli4, Angelo Lupi4, Vito Vitale4, Massimo Del Guasta5, Paolo Grigioni6, Riikka Väänänen1, Ella-Maria Duplissy1, Tuukka Petäjä1, and Markku Kulmala11Department of Physics, University of Helsinki, P.O. Box 64, FI -00014 Helsinki, Finland 2Finnish Meteorological Institute, Air Quality Research, P.O. Box 503, FI -00101 Helsinki, Finland 3CERN, CH-1211 Geneva, Switzerland 4Institute of Atmospheric Sciences and Climate, Italian National Research Council, 40129 Bologna, Italy 5Istituto Nazionale di Ottica, INO-CNR, I-50019 Sesto Fiorentino (FI), Italy 6E NEA Laboratory for Observations and Analyses of Earth and Climate , C.R. Casaccia , I-00123 S.Maria di Galeria (RM) , Italy
Abstract. An Air Ion Spectrometer (AIS) was deployed for the first time at the Concordia station at Dome C (75°06’ S, 123°23’ E; 3220 m above sea level), Antarctica during 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 dataset 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). On days without observations of the foregoing processes or other anomalies, i.e. event-free days, the concentration 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 work better for the NPF events characterized by a fast particle GR, whereas the latter method usually worked better when the GR was slow. The formation rate of 2-nm positive ions (J2+) was calculated for all the NPF events for which a GR in the 2–3 nm size range could be determined. On average, J2+ was about 0.014 cm−3 s. 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. 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 cleavage of cloud condensation nuclei (CCN), possibly related to the instrumental behaviour under the extremely cold condition. For the wind-induced ion formation, our observation suggested that the ions likely from came more atmospheric nucleation of vapours released from the snow than from mechanical charging of shattered snow flakes and ice crystals.
Chen, X., Virkkula, A., Kerminen, V.-M., Manninen, H. E., Busetto, M., Lanconelli, C., Lupi, A., Vitale, V., Del Guasta, M., Grigioni, P., Väänänen, R., Duplissy, E.-M., Petäjä, T., and Kulmala, M.: Features in air ions measured by an Air Ion Spectrometer (AIS) at Dome C, Atmos. Chem. Phys. Discuss., doi:10.5194/acp-2017-311, in review, 2017.