| Summary: | The ability of an aerosol to act as an INP depends on the ambient temperature, with more aerosols acting as INPs at colder temperatures. Therefore, as an airmass precipitates, the most active INPs are preferentially removed. However, the lifecycle of INPs from their emission to their removal via ice nucleation remains unknown. Simultaneously, isotopic fractionation during precipitation formation produces a higher abundancy of heavy stable water isotopes (SWI) in precipitation relative to the air where the precipitation grows. This removal of heavy isotopes from the air acts as a fingerprint of how much water vapour has been removed from an airmass. By studying both the concentration of INPs and the SWI composition in precipitation, we can gain insight into the lifecycle of INPs. We therefore conducted long-range snow sampling transects over the mountains of the Norwegian Arctic during snowfall. The samples were analyzed for the concentration of INPs. In conjunction, the SWI composition of the samples was measured. Additionally, meteorological data and back trajectories were used to interpret the observed variability in INPs and SWI composition over the mountains. We find that the INP concentration and SWI composition are highest on the windward slope of the mountain barrier. However, the maxima in INP concentration and SWI composition aren't always collocated, indicating that the source of INPs and precipitable water do not fully coincide. This suggests that a fraction of the INPs originates from the local boundary layer while the majority of the precipitable water is associated with long-range moisture transport.
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