Advancement of High-Resolution Microfluidic Device in Atmospheric Ice Nucleation Research and Integration into Science Teaching
Authors
Swastika Bithi1* (sbithi@wtamu.edu), Pronob Das1, Saman Aria1, Emmanuel Oko2, Nurun Nahar Lata3, Swarup China3, Sanjoy Bahttacharia1, Naruki Hiranuma2
Institutions
1College of Engineering, West Texas A&M University, Canyon, TX; 2Department of Life, Earth, and Environmental Sciences, West Texas A&M University, Canyon, TX; 3Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, Richland, WA
Abstract
Ambient ice-nucleating particles (INPs) constitute a crucial subset of aerosol particles, playing a vital role in the heterogeneous formation of ice crystals under ice supersaturation conditions. However, uncertainties persist in understanding aerosol radiative forcing and feedback associated with INPs. The research addresses the challenge of comprehending atmospheric ice formation in mixed-phase clouds where immersion freezing is the dominant mechanism. This motivates the community’s interest in quantifying and improving prognostic skills for INP number concentrations. To address these gaps, an affordable, offline microfluidic freezing assay system was developed to measure INP concentration. The system’s performance was verified using known ice nucleation active compounds in immersion mode and high-latitude soil samples. Two novel microfluidic droplet trapping circuits featuring static droplet arrays with 60 interconnected loops (15 nanoliters) and 720 loops (1.5 nL) were fabricated to simulate cloud droplet–relevant sizes. Freezing properties of Snomax®, illite NX, nanocrystalline cellulose (NCC), and Alaskan soil samples were examined to reproduce previous laboratory results with microliter freezing assays within marginal uncertainties for different droplet volumes. Results indicated consistency in the highest freezing temperature and efficiency of Snomax® as well as the lowest freezing temperature and efficiency of NCC for both techniques. Positive controls with known suspension samples were established, affirming the microfluidic device’s reliability. The microfluidic device demonstrated an INP detection limit per unit mass of 105 to 1013 per gram over the temperature range of −5 to −35°C, verifying its applicability to atmospherically relevant freezing conditions and providing accurate data for parameterization development. Lastly, the tools and approaches developed in this work are intended to be integrated into science teaching at a primarily undergraduate Hispanic-serving institute, contributing to disseminating knowledge and fostering a deeper understanding of ice nucleation processes among students.