A regional aerosol growth event during the onset of sea ice melt

Aerosol particles are a key player in the Arctic climate as they act as a surface for cloud droplet condensation and ice nucleation, subsequently affecting the radiative properties of clouds. In the Arctic, interactions between the ocean, sea ice, and atmosphere strongly influence the production and transformation of aerosol particles, but the mechanisms controlling particle number concentrations and size distributions are still poorly constrained. Marine organic gas-phase compounds are known to play an important role in initiating new particle formation and sustaining particle growth to climatically relevant sizes with e.g. potential to serve as cloud condensation nuclei. However, substantial knowledge gaps remain in our understanding of their sources and processes, and quantifying the role of secondary aerosol formation and growth in shaping cloud-active aerosol populations remains a challenge.Spring and the important start of the melt period is a particularly under-sampled season over the Arctic pack ice, due to difficult ice conditions leading to logistic challenges. In 2023, the ARTofMELT (Atmospheric rivers and the onset of sea ice melt) expedition on board the Swedish icebreaker Oden set out to cover this crucial time period, when the aerosol population transitions from haze conditions dominated by long-range transport to being characterized by local sources and corresponding processes.Here, we present measurements of a large-scale aerosol growth event over the Arctic pack ice, in the middle of the seasonal transition into summer. The growth event was preceded by a storm, followed by long-lasting fog, and sustained over several days and across hundreds of kilometers. By combining the broad range of aerosol instrumentation onboard with data from nearby monitoring stations at Villum (North Greenland) and Zeppelin (Svalbard) observatories, trace gas measurements, air source analysis (ie. water vapor isotopes and air parcel modeling), and regional model simulations, we investigate factors defining the origin of the event and its potential impact.