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., Bigg et al., 2001; Rogers, 1996; Fountain and Ohtake, 1985; 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 Fig. 1). References: Ardon-Dryer, K. and Levin, Z.: Atmos. Chem. Phys., 14, 5217-5231, 2014. Belosi, F., and Santachiara, G.: Atmos. Res., 145–146, 105–111, 2014. Bigg, E. K.: Tellus B, 48, 223–233, 1996. Fountain, A. G., and Ohtake, T.: 1985: Climate Appl. Meteor., 24, 377–382, 1985. Mason, R. H. et al.: Atmos. Chem. Phys., 16, 1637–1651, 2016. Rogers, D. C. et al.: J. Atmos. Oceanic Technol., 18, 725–741, 2001.

Non-proteinaceous and proteinaceous biological aerosols are abundant within the atmosphere and have the potential to impact the climate through cloud and precipitation formation. In this study, we present the differences in the laboratory-measured freezing capabilities of the non-proteinaceous and proteinaceous biological materials to determine which has more potential to impact the ice nucleation in the clouds. As non-proteinaceous surrogates, we examined multiple cellulose materials (e.g., microcrystalline and nanocrystalline cellulose) whose sizes range from ~100 nm to >100 μm (according to manufacturer report). For proteinaceous proxies, we looked at different gram-negative bacteria, such as Pseudamonas aeruginosa, Escherichia coli, Serratia marcescens, Citrobacter freundii, and Snomax, (which contains P. syringae) that can be found around the proximity of the Texas Panhandle. By using the Cryogenic Refrigeration Applied Freezing Test (CRAFT) system, we estimated immersion freezing efficiency (i.e., ice nucleation activity scaled to a unit of mass) of each sample at the temperatures greater than -30°C. We have observed that not all gram-negative bacteria has high immersion freezing activity, but the few do have a warmer temperature onset (>-20 °C) than the cellulose used. For those that did not exhibit substantial freezing efficiencies, they had similar freezing properties as the broth, in which the bacteria were incubated, as well as the cellulose materials examined. These observations suggest the presence and potential importance of bacterial cellulose in the atmospheric ice nucleation. From here, we need to conduct more in-depth investigation in the effects of a wider variety of atmospherically relevant biological aerosols to get a better understanding of the effects of said aerosols on overall aerosol-cloud interactions. Acknowledgments: K. Cory would like to acknowledge NSF-EAPSI and JSPS Summer Program for the travel fellowship support. N. Hiranuma acknowledges financial aids by the Higher Education Assistance Fund (HEAF), WTAMU Office of Graduate School and Killgore Research Center.