PIs: André Ehrlich, Andreas Macke, Susanne Crewell

The properties of prevailing aerosol particles, especially the number and chemical composition of Ice Nucleating Particles (INP) and Cloud Condensation Nuclei (CCN), may significantly influence the microphysicaland radiative properties of Arctic clouds. Hence, aerosol particles, especially INP and CCN, and their respective chemical nature, sources and effects need to be considered, when trying to quantify the energy budget of the Atmospheric Boundary Layer (ABL) in the Central Arctic. This is a key issue for an improved understanding of the Arctic response to Global Warming (Arctic Amplification).

Information concerning the concentrations of Arctic INP, their chemical nature (mineral and/or organic), and their origin (local sources or long range transport) is sparse, and therefore the main focus of this proposal. Although CCN–related information is more abundant, we consider it important and complementary in the context of this proposal. To understand Arctic INP and CCN, and in a more general sense the Arctic aerosol, the existing aerosol particles, and their potential local marine sources [i.e., sea surface micro layer (SML) and bulk seawater], need to be characterized chemically and physically (e.g., with respect to their ice nucleation potential).

To scope with these questions we plan to carry out ship–based (RV Polarstern, PASCAL, MOSAiC) measurements of the aerosol particle and CCN size distributions, aerosol particle volatility and hygroscopicgrowth behaviour, and aerosol particle ice nucleation behaviour. In addition, we will quantify the ice nucleation potential of SML material and the bulk seawater. Furthermore, we will chemically characterize atmospheric aerosol particles by means of in–situ aerosol mass spectrometry (AMS), as well as bulk and size–resolved sampling and subsequent offline analysis for specific constituents, including organic material of marine biological origin. SML as well as bulk seawater samples, as potential sources of marine organic particulate material, will be chemically characterized in a similar way to the aerosol samples. From the suggested measurements we expect quantitative information concerning the concentrations and the nature (e.g. mineral and/or organic) of INP and CCN in the Arctic, as well as in–sight into the INP’s and CCN’s possible origin (e.g. sea surface micro layer, bulk seawater, transport).

Due to the sparseness of the existing information, such data is valuable in itself. The results gained provide input and/or constraints for future LES modelling of the Arctic ABL and Earth system models, and hence contribute to a better understanding of the energy budget of the ABL in the Central Arctic, a key issue for an improved understanding of the Arctic response to Global Warming (”Arctic Amplification”).

 In order to test the hypothesis, we will address the following central questions:

• What are the INP, CCN, and aerosol number concentrations in the Central Arctic atmosphere?

• Can we draw conclusions concerning the Arctic INP’s nature (mineral, organic)?

• Are there INP in the sea surface micro layer (SML) and/or the bulk seawater, which could possibly contribute to the arctic IN population?

• What is the chemical composition of the Arctic aerosol, the Artic sea surface micro layer, and the bulk seawater, and are there relationships with observed CCN and INP?