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

Abstract

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 μm³ cm⁻³, and at their lowest during the austral winter with corresponding values of 15 cm⁻³ and 0.009 μm³ 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

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

“…3e). This NPF event was associated with winds from the contaminated sector (10-90 • ) and possibly affected by the diesel generator of the station and motor vehicle pathways (Järvinen et al, 2013). These NPF events occurred after sunrise between about 00:00 and 06:00 UTC (between 08:00 and 14:00 in the local UTC + 8:00 time zone), which is in line with the proposed importance of photochemistry in NPF events and particle growths (Kulmala and Kerminen, 2008;Ehn et al, 2014;Kulmala et al, 2014).…”

“…and a minimum distance of 1100 km from the coastline (Becagli et al, 2012). Measurements were taken at the same sampling site used by Järvinen et al (2013) and Becagli et al (2012), located upwind in the direction of the prevailing wind at a distance of about 1 km southwest of the main station buildings. The northeastern direction is therefore considered as the contaminated sector (10-90 • ), due to local emissions from diesel generators and motor vehicles.…”

“…A differential mobility particle sizer (DMPS), the same used by Järvinen et al (2013), was responsible for recording the number size information of total aerosol particles. The DMPS classifies particles of mobility sizes between 9 and 550 nm.…”

“…At the Norwegian Troll station in the inner region of Queen Maud Land, particle number size distributions in the size range 30-800 nm have been measured over several years (Fiebig et al, 2014). Järvinen et al (2013) presented a 2-year record of particle number size distributions in the size range of 10-600 nm measured at the Italian-French Concordia station at Dome C on the upper Antarctic Plateau, and observed clear signs of atmospheric NPF. However, since their measurement size range started at 10 nm particle diameter, there was no information on the initial step of the NPF, which is expected to take place at diameters below 2 nm .…”

Unexpectedly high ultrafine aerosol concentrations above East Antarctic sea ice

“…Numerous studies have previously observed enhanced aerosol number concentrations in the AFT (e.g. Ito et al, 1986;Osada et al, 2006;Hara et al, 2011b), and even more have suggested it as the dominant source region of Antarctic aerosol (Ito, 1989(Ito, , 1993(Ito, , 1995Virkkula et al, 2009;Asmi et al, 2010;Järvinen et al, 2013;Koponen et al, 2003). We speculate that the absence of signs of growth in the data presented in this study could be a result of condensational growth halting, possibly due to exhaustion of the precursor source, prior to reaching the measurement location.…”