A full year of aerosol size distribution data from the central Arctic under an extreme positive Arctic Oscillation: insights from the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition
Authors: Boyer Matthew , Aliaga Diego , Pernov Jakob Boyd , Angot Hélène , Quéléver Lauriane L. J. , Dada Lubna , Heutte Benjamin , Dall'Osto Manuel , Beddows David C. S. , Brasseur Zoé , Beck Ivo , Bucci Silvia , Duetsch Marina , Stohl Andreas , Laurila Tiia , Asmi Eija , Massling Andreas , Thomas Daniel Charles , Nøjgaard Jakob Klenø , Chan Tak , Sharma Sangeeta , Tunved Peter , Krejci Radovan , Hansson Hans Christen , Bianchi Federico , Lehtipalo Katrianne , Wiedensohler Alfred , Weinhold Kay , Kulmala Markku , Petäjä Tuukka , Sipilä Mikko , Schmale Julia , Jokinen Tuija 
Published: January 2023

Abstract. The Arctic environment is rapidly changing due to accelerated warming in the region. The warming trend is driving a decline in
sea ice extent, which thereby enhances feedback loops in the surface energy
budget in the Arctic. Arctic aerosols play an important role in the
radiative balance and hence the climate response in the region, yet direct observations of aerosols over the Arctic Ocean are limited. In this study,
we investigate the annual cycle in the aerosol particle number size
distribution (PNSD), particle number concentration (PNC), and black carbon
(BC) mass concentration in the central Arctic during the Multidisciplinary
drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition.
This is the first continuous, year-long data set of aerosol PNSD ever collected over the sea ice in the central Arctic Ocean. We use a k-means
cluster analysis, FLEXPART simulations, and inverse modeling to evaluate
seasonal patterns and the influence of different source regions on the
Arctic aerosol population. Furthermore, we compare the aerosol observations
to land-based sites across the Arctic, using both long-term measurements and
observations during the year of the MOSAiC expedition (2019–2020), to
investigate interannual variability and to give context to the aerosol
characteristics from within the central Arctic. Our analysis identifies
that, overall, the central Arctic exhibits typical seasonal patterns of
aerosols, including anthropogenic influence from Arctic haze in winter and secondary aerosol processes in summer. The seasonal pattern corresponds to the global radiation, surface air temperature, and timing of sea ice
melting/freezing, which drive changes in transport patterns and secondary aerosol processes. In winter, the Norilsk region in Russia/Siberia was the
dominant source of Arctic haze signals in the PNSD and BC observations, which contributed to higher accumulation-mode PNC and BC mass concentrations in the central Arctic than at land-based observatories. We also show that the
wintertime Arctic Oscillation (AO) phenomenon, which was reported to achieve
a record-breaking positive phase during January–March 2020, explains the
unusual timing and magnitude of Arctic haze across the Arctic region compared to longer-term observations. In summer, the aerosol PNCs of the nucleation and Aitken modes are enhanced; however, concentrations were
notably lower in the central Arctic over the ice pack than at land-based
sites further south. The analysis presented herein provides a current
snapshot of Arctic aerosol processes in an environment that is characterized
by rapid changes, which will be crucial for improving climate model
predictions, understanding linkages between different environmental
processes, and investigating the impacts of climate change in future Arctic
aerosol studies.