Characteristics of local ship emissions over the central Arctic Ocean

The Arctic radiative balance is mainly determined by the high albedo of sea ice and snow, which reflect incoming solar radiation. However, climate change is accelerating warming in the region leading to sea-ice retreat and a resulting amplification of warming via the seaice albedo feedback. Melting ice also enhances ocean–atmosphere interactions, increasing emissions of natural aerosols like sea salt and dimethyl sulfide. These aerosols directly influence the climate by absorbing heat or by reducing surface albedo through wet and dry deposition. A subset of aerosols known as cloud condensation nuclei (CCN) and ice nucleating particles (INP) may also be activated into cloud, changing the cloud radiative properties. With declining ice cover, commercial shipping in the Arctic is expected to rise, yet its atmospheric impact remains poorly understood.

This study investigates ship emission related pollution using year-long observations from the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition. We analyze particle concentrations, size distributions, chemical composition, and CCN properties with regards to seasonality and specific environmental conditions. During major ship pollution events, particle number concentrations (3–500 nm) increased by more than two orders of magnitude. Emitted aerosols were primarily composed of organics (49 %), black carbon (19 %), and sulfate (26 %), though sulfate levels were unexpectedly lower than in the background.

The annual cycle of the particles size distribution (10-500nm) was found to be relatively stable with a predominant Aitken mode, although specific environmental conditions caused shifts in particle sizes. Periods of fog with high relative humidity caused particles to grow which is usually associated to increased condensation. Inversely, NPF events during the polar day combined to pollution created a cluster of smaller sized particles. While CCN concentrations increased at all supersaturation levels during pollution events, the particles were smaller and less hygroscopic, leading to a lower activation ratio.

In summary, a probable intensification of shipping activities in the future would lead to emissions of large amounts of particles of the Aitken mode into the pristine arctic troposphere and to substantial changes in aerosols concentrations and properties. These changes may strongly impact aerosol–cloud interactions and overall radiative forcing.