What we can learn from aerosol size distribution measurements over the spring Arctic pack ice

Aerosol- cloud interactions remain among the most uncertain key parameters in the fast-changing Arctic climate system, in large part due to a lack of observational data from this hardly accessible region. The spring-summer transition is a particularly under sampled time period, due to harsh ice conditions. Here, we present five weeks of aerosol size distribution measurements over the spring Arctic pack ice, including more than 30 hours of in-cloud data, obtained during the ARTofMELT 2023 expedition. A setup of three inlets, including a whole-air, an interstitial, and a counterflow virtual impactor inlet, were used to cover the full aerosol population as well as both the activated and interstitial aerosol when in cloud. We will show an overview of the collected observations and the link between the size distribution properties and parallel measured aerosol parameters such as chemical tracers, as well as an air mass source analysis. Fog events were recorded during a range of aerosol conditions, allowing us to study the activated fraction when concentrations span from under 20 particles per cc, to over 150. The dataset also features several distinct regimes where different processes such as blowing snow, new particle formation, and secondary ice production dominate or influence the aerosol population, and we will demonstrate how the regimes are characterized by the dominant mode of the size distribution.