Multi-seasonal measurements of the ground-level atmospheric ice-nucleating particle abundance on the North Slope of Alaska

Abstract. Atmospheric ice-nucleating particles (INPs) are an important subset of aerosol particles that are responsible for the heterogeneous formation of ice crystals. INPs modulate arctic cloud phase (liquid vs. ice), resulting in implications for radiative feedbacks. The number of arctic INP studies investigating specific INP episodes or sources has recently increased. However, existing studies are based on short-duration field data and long-term datasets are lacking. Continuous, long-term measurements are key to determining the abundance and variability of ambient arctic INPs and for constraining aerosol-cloud interactions, for example, to verify and/or improve simulations of mixed-phase clouds. Here, we present the first long-duration INP dataset from the Arctic: two years of immersion mode INP concentrations (n_INP) measured continuously at the National Oceanic and Atmospheric Administration's Barrow Atmospheric Baseline Observatory on the North Slope of Alaska. A portable ice nucleation experiment chamber (PINE-03), which simulates adiabatic expansion cooling, was used to directly measure the ground-level INP abundance with an approximately 12-minute time resolution from October 2021 to December 2023. We document PINE-03 n_INP measurements over a wide range of heterogeneous freezing temperatures from −16 to −31 °C from which we introduce new season-specific parameterizations suitable for modeling mixed-phase clouds. Collocated aerosol and meteorological data were analyzed to assess the correlation between ambient n_INP, air mass origin region, and meteorological variability. Our findings suggest (1) very high freezing efficiency of INPs across the measured temperatures (≈ 2 x 10⁸ – 10¹⁰ m⁻² for from −16 to −31 °C), which is a factor of 10 − 1000 times greater efficiency as compared to that found in the previous mid-latitude INP measurements in autumn using the same instrument; (2) surprisingly high n_INP for the examined temperatures throughout the year that were not measured by PINE-03 at other sites; and (3) high n_INP in spring, possibly related to arctic haze episodes.