Seasonal cycle and modal structure of particle number size distribution at Dome C, Antarctica

We studied new particle formation and modal behavior of ultrafine aerosol particles on the high East Antarctic plateau at the Concordia station, Dome C (75°06' S, 123°23' E). Aerosol particle number size distributions were measured in the size range 10-600 nm from 14 December 2007 to 7 November 2009. We used an automatic algorithm for fitting up to three modes to the size distribution data. The total particle number concentration was low with the median of 109 cm-3. There was a clear seasonal cycle in the total particle number and the volume concentrations. The concentrations were at their highest during the austral summer with the median values of 260 cm-3 and 0.086 ?m3 cm-3, and at their lowest during the austral winter with corresponding values of 15 cm-3 and 0.009 ?m3 cm-3. New particle formation events were determined from the size distribution data. During the measurement period, natural new particle formation was observed on 60 days and for 15 of these days the particle growth rates from 10 to 25 nm in size could be determined. The median particle growth rate during all these events was 2.5 nm h-1 and the median formation rate of 10 nm particles was 0.023 cm-3 s-1. Most of the events were similar to those observed at other continental locations, yet also some variability in event types was observed. Exceptional features in Dome C were the winter events that occurred during dark periods, as well as the events for which the growth could be followed during several consecutive days. We called these latter events slowly growing events. This paper is the first one to analyze long-term size distribution data from Dome C, and also the first paper to show that new particle formation events occur in central Antarctica.