Figure
3. Time series showing the ice-nucleating activity (expressed as the
temperature at which a concentration of 0.1 INP L-1(T [INP]=0.1)) throughout the campaign
alongside DMS, aerosol surface area and eBC. In both panels a and b, the
tops of the grey bars represent T [INP]=0.1 in
the surface mixed layer (i.e. at ship level, 20 m above mean sea level),
with the width of the bar representing the period over which air was
sampled. The hatched grey bars are limiting values (where droplet
freezing was indistinguishable from the control experiments). a) The
time series of the daily average surface area of aerosol per litre
(blue), the dimethyl sulfide (DMS) concentration (green) and the
equivalent black carbon (eBC) concentrations (red) measured in the
aerosol are shown. b) The values ofT [INP]=0.1 measured above the surface mixed
layer (using the SHARK balloon-borne sampler) are shown against those at
taken at ship level (grey bars). The red triangles are theT [INP]=0.1 for the summed INP concentrations
across all size categories (comparable to the measurements at ship
level), while the crosses indicate theT [INP]=0.1 associated with each size category
(circles indicate limiting values. The dates for the respective periods
are: MIZ 02/08/18-03/08/18, Clean-air station 10/08/18-11/08/18,
Ice-breaking 03/08/18-16/08/18, Ice floe 16/08/18-15/09/18, Ice-breaking
15/09/18-19/09/18, MIZ 19/09/18.
We also show the ice-nucleating activity in the form of ice-active sites
per unit surface area (n s) in Figure 4. The
variable n s provides a means of comparing the
activity of aerosol on a per unit surface area basis. It is striking
that the activity of the samples in the central Arctic are often much
more active than aerosol over the Southern Ocean [McCluskey et
al. , 2018a] or from the north Atlantic [McCluskey et al. ,
2018b]. This shows the aerosol in this location are much more
ice-active than aerosol in other remote marine environments.