Annual Cycles in Ice Nucleating Particle Concentrations at Four Arctic Locations

Filter samples collected on quartz fiber filters at four Arctic measurement stations, Alert, Barrow, Ny-Ålesund and Villum were analyzed with respect to number concentrations of ice nucleating particles (N_INP). Measurements were done following the method proposed by Conen et al. (2012), examining immersion freezing: a filter punch (1 mm in diameter) was put into every one of the 96 tubes of a PCR tray, where each tube contained 50 microliter of pure water; the tray was sealed and immersed in the cooling bath of a thermostat and cooled down with a cooling rate of 1K/min; during the cooling, every 6 s a picture of the tray was taken from above, and discrimination between liquid and frozen droplets was done. The obtained temperature dependent freezing curves were used to derive N_INP in the temperature range from -5°C down to -20°C.

For Ny Alesund, samples from spring and summer months were examined, while a yearly coverage existed for the other stations. Differing values of N_INP were observed during the year, and in general during summer and fall, particles were more ice active than during winter and early spring, indicating that different sources of ice nucleating particles contributed to the pan-arctic area, their influence varying with season. The lowest values determined for the Arctic samples were about 1 order of magnitude lower than N_INP determined from precipitation samples collected in North America and Europe (Petters & Wright 2015), but the highest values were comparable, pointing at a biogenic origin from either the biosphere (e.g., from fungal spores or bacteria) or from marine sea spray (e.g., from algae or bacteria). These biogenic ice nucleating particles might become more abundant as the Arctic warms, with potential influences on cloud properties as e.g., the lifetime of the persistent Arctic stratiform clouds.

This study gives first insights into yearly cycles of ice nucleating particles in the Arctic, but it also reveals open questions and suggests future pathways concerning their examination.

Literature:

Conen et al., 2012, Atmos. Meas. Tech., doi: 10: .5194/amt-5-321-2012.

Peters & Wright, 2015, Geophys. Res. Lett., doi: 10.1002/2015gl065733.