Mixing State of Refractory Black Carbon, Optical Properties and Sources of Aerosol Particles in the European Arctic Marine Boundary Layer

ARUN BABU SUJA, Thomas Müller, Mira L. Pöhlker, Heike Wex, Andreas Held, Manuela van Pinxteren, Yifan Yang, Philipp Oehlke, Sabine Lüchtrath, Holger Siebert, Theresa Mathes, Maik Merkel, Birgit Wehner, Leibniz Institute for Tropospheric Research, Leipzig,Germany

     Abstract Number: 11
     Working Group: Aerosol Physics

Abstract
Aerosol particles are of critical importance to the Arctic climate system. However, there are minimal direct observations of aerosol particles over the Arctic Ocean, especially using shipborne platforms. With this in mind, we have conducted aerosol measurements aboard the German ice breaker research vessel Polarstern during the ATWAiCE (Atlantic Water pathways to the ice in the Nansen Basin and Fram Strait) cruise from June to August 2022. The aerosol characteristics were evaluated based on the influence of the airmass trajectories and divided into eight legs (L1- L8). The highest values of refractory black carbon (rBC) and light scattering were observed during L1 (up to 700N) (avg. rBC ~ 40 ng m-3, avg. σsca.525nm ~ 29 Mm-1), where the airmass trajectories were dominated by the southeastern urban continental sites. The measurement period during L4 (15th- 20th July) was influenced by a warm airmass intrusion when the ship was in the northern part of the marginal ice zone. We observed significant changes in the optical properties during this period, with major contributions of biomass burning emissions from Siberia. The rBC values have increased almost eightfold compared to the previous period in which the mass median diameter of rBC cores were >260 nm compared to ~155 nm during L1. Further, the observed coating thickness of rBC was lower (median ~ 11 nm) than the observations from other periods. The lowest values of scattering/absorption in the central Arctic were observed during 23rd - 30th July when the ship was mostly traversing through the densely packed ice associated with northeasterly air masses traversing the Arctic Ocean. It was also noted that the aerosol concentrations were relatively higher during 01st - 03rd August, which was associated with more air masses being transported through the oceanic sectors from the south, including the North Sea and Norwegian Sea when the ship crossed the outer edge of the marginal ice zone.