The effect of sea ice conditions and Arctic Oscillation on the aerosol size distribution in Ny-Ålesund, Svalbard

In the Arctic Ocean both the sea ice extent and the sea ice thickness have decreased dramatically during recent years. This has also most probably caused changes in airmass routes and lead to unusually negative Arctic Oscillation (AO) index especially in winter. It is likely that the aerosol production in the Arctic will increase with the declining sea ice cover. In this study we used a five-year of the aerosol size distribution measurements from the Zeppelin station in Ny-Ålesund, Svalbard. We compared trajectory-, sea ice- and Arctic Oscillation-index (AO-index) data to find out if aerosol size distribution properties over sea ice differ from properties over open sea and also if there are differences between negative AO-index (AO-) and positive AO-index (AO+). We divided the data into four sectors and three seasons (spring, summer, and autumn and winter). During autumn and winter the number concentration distribution is clearly different over open sea than over sea ice. However the sea ice concentration doesn't have an effect to the number concentration. The total number concentration is smaller over open sea (less than 60 cm-3) than over ice (range from 14 to 120 cm-3). During spring, the aerosol number concentration is dominated by the accumulation mode particles. During summer the Aitken mode number concentrations are higher than accumulation mode number concentrations. The lower the AO-index is the bigger the particles are. During summer the number concentration distribution is complete different than during autumn and winter. Differences between AO- and AO+ situations were small. Seasonality was clearly important. It is clear that sea ice has an effect to the aerosol size distribution properties, but it doesn't seem to matter what kind of ice concentration there is. Also the AO-index has an effect to the aerosol size distribution, but weather the AO and sea ice together have an effect to the aerosol properties is not so clear than the effect of the sea ice itself. In the future, when sea ice extent probably is decreasing the open sea situations are going to be more common than sea ice situations. Then it is possible that nucleation mode number concentration increases with the decreasing sea ice.