Size distribution and ionic composition of marine summer aerosol at the continental Antarctic site Kohnen

We measured aerosol size distributions and conducted bulk as well as size segregated aerosol sampling during two summer campaigns in January 2015 and January 2016 at the continental Antarctic station Kohnen (Dronning Maud Land). Physical and chemical aerosol properties differ conspicuously during the episodic impact of an outstanding low pressure system in 2015 (LPS15) compared to the prevailing clear sky conditions (CSC): The about three days persisting LPS15, located in the eastern Weddell Sea, was associated with marine boundary layer (MBL) air mass intrusion, enhanced condensation particle concentrations (1400±700 cm-3 compared to 250±120 cm-3 during CSC; mean ± SD), occurrence of a new particle formation (NPF) event exhibiting a continuous growth of particle diameters (Dp) from 12 nm to 43 nm over 44 hours (growth rate 0.6 nm h-1), peaking methane sulfonate (MS-), non-sea salt sulfate (nss-SO42-) and Na+ concentrations (190 ng m-3 MS-, 137 ng m-3 nss-SO42-, and 53 ng m-3 Na+ compared to 24±15 ng m-3, 107±20 ng m-3 and 4.1±2.2 ng m-3, respectively, during CSC), and finally an increased MS-/nss-SO42- mass ratio ßMS of 0.4 up to 2.3 (0.21±0.1 during CSC) comparable to typical values found at coastal Antarctic sites. Throughout the observation period a larger part of MS- could be found in super micron aerosol compared to nss-SO42-, i.e. (10±2) % by mass compared to (3.2±2) %, respectively. On the whole, during CSC aged aerosol characterized by an usually mono-modal size distribution around Dp = 60 nm was observed. Although our observations indicate that sporadic impacts of coastal cyclones were associated with enhanced marine aerosol entry, at large aerosol deposition on-site during austral summer should be dominated by the typical steady CSC.