Biogenic Sources of Ice Nucleating Particles at the High Arctic Site Villum Research Station

The radiative balance in the Arctic region is sensitive to in-cloud processes, which principally depend on atmospheric aerosols, including ice nucleating particles (INPs). High temperature INPs (active at ≥-15 °C) are common in the Arctic. While laboratory and limited in situ studies show that the high-temperature active INPs are associated with bioaerosols and biogenic compounds, there is still little quantitative insight into the Arctic biogenic INPs and bioaerosols. We measured concentrations of bioaerosols, bacteria, and biogenic INPs at the Villum Research Station (VRS, Station Nord) in a large number of snow (15) and air (51) samples. We found that INPs active at high subzero temperatures were present both in spring and summer. Air INP concentrations were higher in summer (18 INP m^-3 at ≥-10 °C) than in spring (<4 INP m^-3 at ≥-10 °C), when abundant INPs were found in snowfall (1.4 INP mL^-1 at ≥-10 °C). Also, in summer, a significantly higher number of microbial and bacterial cells were present compared to the spring. A large proportion (60%-100%) of INPs that were active between -6 °C and -20 °C could be deactivated by heating to 100 °C, which was indicative of their predominantly proteinaceous origin. In addition, there was a significant linear regression between the summer air concentrations of INPs active at ≥-10 °C and air concentrations of bacterial-marker-genes (p < 0.0001, R² = 0.999, n = 6), pointing at bacterial cells as the source of high-temperature active INPs. In conclusion, the majority of INPs was of proteinaceous, and possibly of bacterial, origin and was found in air during summer and in snowfall during springtime.