Immersion freezing efficiencies of ambient particles collected from five different regions across latitudes

This poster presents immersion freezing efficiencies of ambient particles collected from different latitudes between 79 °N and 75 °S. We collected particles using aerosol impactors at five different geographic locations, including i) the Atlantic sector of the Arctic, ii) an urban area in Europe, iii) a rural location in the U.S., iv) a mid-latitude agricultural site in the U.S., and v) the Antarctica peninsula area around Weddell Sea, representing unique particle episodes and atmospheric conditions. Then, we used an offline droplet-freezing assay instrument to measure fine-temperature-resolved ice-nucleating particle (INP) concentrations at T >= -25 °C (with a detection capability of >0.0001 per L of air) for each region. Our preliminary results show INP concentrations in polar regions are - as expected - lower compared to mid-latitudes. Low concentrations of high-latitude INPs have been reported in other previous studies (e.g., Fountain and Ohtake, 1985; Bigg, 1996; Rogers et al., 2001; Mason et al., 2015; Ardon-Dryer and Levin, 2014; Belosi and Santachiara, 2014). Another important observation is the high variability of mid-latitude INP concentrations. A difference in the aerosol episode and properties may be key for such a high variability in the mid-latitude region. The composition of INPs varies, but it typically includes dust-related minerals, pollution aerosol, biogenic nuclei and marine microlayers. It is therefore important to comprehensively study realistic representation of both INP concentration and composition (ultimately for model parameterization) and their relevance to the aerosol-cloud interactions with a better temporal resolution under different atmospheric states and a wider spatial coverage of INP sampling sites (see Figure below).