Ice-nucleating particle concentrations from June-August 2023 in Narsaq and Narsarsuaq in southern Greenland

This dataset contains ice-nucleating particle (INP) concentrations based on filter samples collected between June-August 2023 in Narsaq and Narsarsuaq, with two measurement sites per location. Small solar and battery-powered stations were located in the outwash plain (61.20032°, -45.32882°) in Narsarsuaq, and at a col nearby at 300 m a.s.l (61.2061254°, -45.3118504°). In Narsaq, measurements were taken at Narsaq International Research Station (NIRS) (60.9157503°, -46.053326°) and on Tasigaaq hill nearby at 372 m a.s.l. (60.9210617°, -46.0274668°). Aerosol filter sampling was performed using custom-built filter samplers, consisting of a stainless-steel inlet, an in-line plastic filter holder (Whatman®, Cytiva, USA), a mass flow controller (Sensirion AG, Switzerland), and a pump (KNF Neuberger GmbH, Germany). NucleporeTM polycarbonate filters (47 mm diameter, 0.2 μm pore diameter) were prepared according to the protocol described in Barry et al. (2021), and inserted into the holders under clean conditions. Aerosol sampling was performed at a flow of 5-10 std L min-1. Atmospheric INP concentrations were determined from droplet-freezing assays using the Sion Ice Crystallization Experiment (SPICE), an immersion-mode INP measurement set-up. Aerosols were washed of the filters by placing them in a tube rotator at 60 rpm for 20 min using 12 mL of molecular-biology-free reagent water (Cat. No. W4502, Sigma Aldrich), with two 15-fold dilutions prepared thereafter. 50 μL droplets were pipetted 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-nucleating particle concentrations (NINP) as a function of temperature T were determined following Vali (1971): $N_{\mathrm{INP}}(T) = -\ln\!\left(\frac{1 - FF(T)}{1 - FF_{\mathrm{background}}(T)}\right)\, \frac{d}{V_d}\,\frac{V_{\mathrm{wash}}}{V_{\mathrm{air}}}$ where d is the dilution factor, Vd the droplet volume (50 μL), Vwash the volume of washing water (12 mL), and Vair the total volume of air sampled on the filter. 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 N_inp_filter_samples.csv Ice-nucleating particle concentrations (L-1) N_inp_lowerCI_filter_samples.csv Lower 95 % confidence interval (L-1) N_inp_upperCI_filter_samples.csv Upper 95 % confidence interval (L-1) N_inp_heat_filter_samples.csv Ice-nucleating particle concentrations (L-1) for samples following heat treatment N_inp_heat_lowerCI_filter_samples.csv Lower 95 % confidence interval (L-1) for samples following heat treatment N_inp_heat_upperCI_filter_samples.csv Upper 95 % confidence interval (L-1) for samples following heat treatment N_inp_h2o2_filter_samples.csv Ice-nucleating particle concentrations (L-1) for samples following H2O2 treatment N_inp_h2o2_lowerCI_filter_samples.csv Lower 95 % confidence interval (L-1) for samples following H2O2 treatment N_inp_h2o2_upperCI_filter_samples.csv Lower 95 % confidence interval (L-1) for samples following H2O2 treatment Structure of each data file: Variable / Column name Description sample_ID Sample ID -27.0, -26.5, -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 Temperatures in °C Metadata file dust samples: filter_samples_metadata.csv Variable / Column name Description sample_ID Sample ID location Sampling location: Narsarsuaq plain, Narsarsuaq col, Narsaq International Research Station (NIRS), Tasigaaq hill lat Latitude (°) of measurement location lon Longitude (°) of measurement location altitude Altitude (m a.s.l.) of measurement location start_date Start date of filter sampling in local time, UTC-2 (yyyy-mm-dd hh:mm) end_date End date of filter sampling, UTC-2 (yyyy-mm-dd hh:mm) 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. Barry, K. R., Hill, T. C. J., Jentzsch, C., Moffett, B. F., Stratmann, F., and DeMott, P. J.: Pragmatic protocols for working cleanly when measuring ice nucleating particles, Atmospheric Research, 250, 105419, https://doi.org/10.1016/j.atmosres.2020.105419, 2021. 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 an 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.