Abstract. Within the framework of the RACEPAC (Radiation–Aerosol–Cloud Experiment in
the Arctic Circle) project, the Arctic aerosol, arriving at a ground-based
station in Tuktoyaktuk (Mackenzie River delta area, Canada), was
characterized during a period of 3 weeks in May 2014. Basic meteorological
parameters and particle number size distributions (PNSDs) were observed and
two distinct types of air masses were found. One type were typical Arctic
haze air masses, termed accumulation-type air masses, characterized by a
monomodal PNSD with a pronounced accumulation mode at sizes above
100 nm. These air masses were observed during a period when back
trajectories indicate an air mass origin in the north-east of Canada. The
other air mass type is characterized by a bimodal PNSD with a clear minimum
around 90 nm and with an Aitken mode consisting of freshly formed
aerosol particles. Back trajectories indicate that these air masses, termed
Aitken-type air masses, originated from the North Pacific. In addition, the
application of the PSCF receptor model shows that air masses with their
origin in active fire areas in central Canada and Siberia, in areas of
industrial anthropogenic pollution (Norilsk and Prudhoe Bay Oil Field) and
the north-west Pacific have
enhanced total particle number concentrations (NCN). Generally,
NCN ranged from 20 to 500 cm−3, while cloud
condensation nuclei (CCN) number concentrations were found to cover a range
from less than 10 up to 250 cm−3 for a supersaturation (SS)
between 0.1 and 0.7 %. The hygroscopicity parameter κ of the
CCN was determined to be 0.23 on average and variations in κ were
largely attributed to measurement uncertainties. Furthermore, simultaneous
PNSD measurements at the ground station and on the Polar 6 research
aircraft were performed. We found a good agreement of ground-based PNSDs
with those measured between 200 and 1200 m. During two of the four
overflights, particle number concentrations at 3000 m were found to
be up to 20 times higher than those measured below 2000 m;
for one of these two flights, PNSDs measured above 2000 m showed a
different shape than those measured at lower altitudes. This is indicative of
long-range transport from lower latitudes into the Arctic that can advect
aerosol from different regions in different heights.
Water Expulsion and Pingo Formation in a Region Affected by Subsidence