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.