Ice-nucleating activity of glacially sourced dust collected in glacial outwash plains in Narsarsuaq, Igaliku, and Kangerlussuaq, Greenland

This dataset contains ice-active mass site densities from dust samples collected in glacial outwash plains in Narsarsuaq, Igaliku, and Kangerlussuaq, Greenland, for temperatures between -26 ° and -7 °C. Samples are separated in sample set 1 and sample set 2. Sample set 1 has been collected along glacier to fjord transects, targeting surface sediments from unvegetated areas. These samples were sieved to < 45 μm. Sample set 2 was collected from both unvegetated and vegetated surfaces and has been kept unsieved. Ice-active mass site densities were determined from droplet-freezing assays using the Sion Ice Crystallization Experiment (SPICE), an immersion-mode ice-nucleating particle (INP) measurement set-up. Suspensions and 10-fold dilutions with mass concentrations ranging from approximately 2 to 0.0002 g L-1 were prepared with molecular-biology-free reagent water (Cat. No. W4502, Sigma Aldrich), and pipetted in 50 μL droplets in two PCR-trays (Cat. No. 781368, Brand, Germany), and inserted in a cooling block, and cooled down to ~-32 °C with a cooling ramp of ~0.33°C min-1. From the optically detected frozen fraction of droplets at each temperature (FF(T)), ice-active mass site densities (nm) as a function of temperature T were determined following Vali (1971): $n_m(T) = -\ln\!\left(\frac{1 - FF(T)}{1 - FF_{\mathrm{background}}(T)}\right)\, \frac{d}{V_d}\,\frac{1}{C_m}$ where d is the dilution factor, Vd the droplet volume (50 μL), and Cm the mass concentration of the initial suspension. FFbackground(T) denotes the fraction frozen of pure water, for which the data is corrected. 95% confidence intervals were computed based on Eq. 2 in Agresti and Coull (1998). The published datafiles contain one merged INP spectrum, calculated as an average of the different dilutions and confidence intervals are reported as absolute concentrations. For compositional information, treatments have been performed on a subset of samples. Heat treatment for heat-labile, likely biological, INPs has been performed by placing the sample tube in a boiling water bath for 20 min (e.g., Daily et al., 2022). For hydrogen peroxide (H2O2) treatment, which removes all organic INPs (e.g., McCluskey et al., 2018), 1 mL of 30 % H2O2 (Cat. No. 216763-100ML, Merck Millipore, Germany) was added to the sample suspension and the sample tube was placed into a boiling water bath with UV light for 20 min. Remaining peroxide was neutralized with small quantities (90 to 130 μL) of 0.1 μm filtered catalase (Cat. No. MPB-210042910-10ML, MP Biomedicals, USA). More detailed descriptions of the data, methods, and results can be found in Bergner et al. (in preparation). Overview data files: Filename Variable nm_dust_samples.csv Ice-active mass site densities (g-1 dust) nm_lowerCI_dust_samples.csv Lower 95 % confidence interval (g-1 dust) nm_upperCI_dust_samples.csv Upper 95 % confidence interval (g-1 dust) nm_heat_dust_samples.csv Ice-active mass site densities (g-1 dust) for samples following heat treatment nm_heat_lowerCI_dust_samples.csv Lower 95 % confidence interval (g-1 dust) for samples following heat treatment nm_heat_upperCI_dust_samples.csv Upper 95 % confidence interval (g-1 dust) for samples following heat treatment nm_h2o2_dust_samples.csv Ice-active mass site densities (g-1 dust) for samples following H2O2 treatment nm_h2o2_lowerCI_dust_samples.csv Lower 95 % confidence interval (g-1 dust) for samples following H2O2 treatment nm_h2o2_upperCI_dust_samples.csv Lower 95 % confidence interval (g-1 dust) for samples following H2O2 treatment Structure of each data file: Variable / Column name Description sample_ID Sample ID -26.0, -25.5, -25.0, -24.5, -24.0, -23.5, -23.0, -22.5, -22.0, -21.5, -21.0, -20.5, -20.0, -19.5, -19.0, -18.5, -18.0, -17.5, -17.0, 16.5, -16.0, -15.5, -15.0, -14.5, -14.0, -13.5, -13.0, -12.5, -12.0, -11.5, -11.0, -10.5, -10.0, -9.5, -9.0, -8.0, -7.5, -7 Temperatures in °C Metadata file dust samples: dust_samples_metadata.csv Variable / Column name Description sample_ID Sample ID location Sampling location: Igaliku, Kangerlussuaq, or Narsarsuaq lat Latitude (°) of sampling location lon Longitude (°) of sampling location sampling_date Sampling date sample_set Sampling set (“1” or “2”) sieving Sieving of sample before INP measurements: “sieved to <45 μm” (sample set 1) or “unsieved” (sample set 2) vegetation_cover Vegetation cover of sampling site: “unvegetated” or “vegetated” Project grants: This work was supported by funding from the Swiss National Science Foundation grant no. 200021_212101, the Swiss Polar Institute grant no. SPI-FLAG-2021-002 Greenfjord, and the ENAC Flagship 2022 ECO-Plains. References: Agresti, A. and Coull, B. A.: Approximate Is Better than “Exact” for Interval Estimation of Binomial Proportions, The American Statistician, 52, 119–126, https://doi.org/10.2307/2685469, 1998. Bergner, N., Marsh, G., Barry, K., Lacher, L., Böhmländer, A., Alden, J., Ahlqvist, C., Altshuler, I., Bröder, L., Farinotti, D., Favre, L., Guillosson, C., Heutte, B., Höhler, K., Pohorsky, R., Weng, J., and Schmale, J.: Ice-nucleating particles in Greenlandic glacial outwash plains, Atmospheric Chemistry and Physics, in preparation. Daily, M. I., Tarn, M. D., Whale, T. F., and Murray, B. J.: An evaluation of the heat test for the ice-nucleating ability of minerals and biological material, Atmospheric Measurement Techniques, 15, 2635–2665, https://doi.org/10.5194/amt-15-2635-2022, 2022. McCluskey, C. S., Ovadnevaite, J., Rinaldi, M., Atkinson, J., Belosi, F., Ceburnis, D., Marullo, S., Hill, T. C. J., Lohmann, U., Kanji, Z. A., O’Dowd, C., Kreidenweis, S. M., and DeMott, P. J.: Marine and Terrestrial Organic Ice-Nucleating Particles in Pristine Marine to Continentally Influenced Northeast Atlantic Air Masses, Journal of Geophysical Research: Atmospheres, 123, 6196–6212, https://doi.org/10.1029/2017JD028033, 2018. Vali, G.: Quantitative Evaluation of Experimental Results and the Heterogeneous Freezing Nucleation of Supercooled Liquids, Journal of the Atmospheric Sciences, 28, 402–409, https://doi.org/10.1175/1520-0469(1971)028%253C0402:QEOERA%253E2.0.CO;2, 1971.