Seasonal Variability of Ice Nucleating Particles (INP) in Southern Sweden

Sammanfattning: Cloud ice crystals are formed by ice-nucleating particles (INPs). The micro-physical properties of clouds, precipitation formation and the life cycle of clouds are strongly influenced by the presence or absence of ice. Therefore knowledge of atmospheric INP concentrations is crucial to improve weather forecasting and climate projections. But global INP concentration vary depending on geographic region, time of the year, their source and also what type of INP being studied. So in-situ measurements which are typically constrained in time and cannot capture more long-term trends such as e.g., a seasonal cycle. Here in this study we investigate daily samples on polycarbonate filter at the Hyltemossa station (Southern Sweden) from March to July 2021 and analyzed their ice nucleating ability. The project involves finding out typical INP concentrations, their variations over time and relationship with other meteorological and aerosol parameters. The main findings we get is INP concentration vary between 0.01 to 1.93 particles L-1 but did not show any trend throughout the whole time and no strong obvious correlation with any of the meteorological parameters. An analysis with frequency distribution of INPs with a freezing temperature of-17 °C showed a significant result which indicates sampled air is well mixed and that the INP active at that temperature originate from long-range transport rather than more local sources. We also compared our measurements with parametrizations based on aerosol particle concentration and ambient air temperature. The latter shows reasonably good agreement, while the former over-predicts the INP concentration.