Seeking the origins of Arctic ice nucleating particles with FLEXPART-WRF

The Arctic region is subject to polar amplification, causing it to warm approximately four times faster than the global average. The predominance of ice and mixed-phase clouds in high latitude regions causes strong uncertainties in the determination of the cloud radiative effect and the cloud feedback. The representation of these clouds in models is therefore a crucial point for climate prediction. Solid and liquid water phases partitioning in mixed-phase clouds is mostly driven by their formation and growth processes, in which aerosol particles play a major role, especially in the Arctic where those particles are scarce. Although ice nucleating particles (INPs) may have relevant impact on weather and climate, their physical and chemical properties stay poorly understood. One of the main reasons is the lack of knowledge about their nature; the latter being mainly determined by their sources and thereby their geographical origins.

In this study, in situ measurements from several recent data-sets are used to determine the likely origins of warm Arctic INPs (activated between -10°C and -20°C). A statistical method is applied on the backtrajectories derived from the lagrangian dispersion model FLEXPART-WRF, allows to characterize the seasonal variability of the identified INPs’ sources encountered over the arctic basin.

The seasonal analysis shows that contributions of continental and marine sources to INPs concentrations are highly time- and space-dependent. Arctic INPs do not come exclusively from local sources and can originate from long-range transport. However, the general strong contribution of sea ice and open ocean regions to high concentrations of INPs, and its seasonal variability, is a clue about the importance of local sources. It emphasizes the hypothesis that marine biologic sources are among the main contributors to INPs emissions in the Arctic, when air masses coming from continental regions are often weak contributors. Also, the discrete strong contribution of sea ice regions, particularly in Autumn, suggests that mechanisms like blowing snow or emission of sea sprays from leads and marginal sea ice could have a relevant impact on Arctic INPs production.

These results show the potential of this approach to characterize the origins of in situ measured species, and call for the method to be used in future studies on aerosols emissions.