Reaching new heights: A vertically-resolved ice nucleating particle sampler operating on Atmospheric Radiation Measurement (ARM) tethered balloon systems

Abstract. Ice nucleating particles (INPs) are a rare yet climatically relevant subset of aerosols that initiate ice formation in mixed-phase clouds, strongly influencing cloud microphysics, precipitation, and Earth’s radiative balance. Despite their significance, ground-based measurements of INPs may not always be representative of those at cloud level, yet vertically-resolved INP measurements remain limited. Here, we introduce PUFIN (Profiling Upper altitudes For Ice Nucleation), a robust, lightweight INP sampler designed for routine deployment on the U.S. Department of Energy Atmospheric Radiation Measurement (ARM) user facility’s tethered balloon system (TBS). PUFIN collects multiple filter samples per flight at up to three altitudes, integrating real-time monitoring of flow, power consumption, and atmospheric conditions, while remaining fully operable from the ground. Multiple deployments at two ARM observatories in Maryland and Alabama demonstrate that PUFIN achieves sufficient aerosol loading to detect INPs down to ~10^-3 L^-1 within as little as 28 minutes of sampling, but typically within an hour. Data from recent deployments reveal altitude-dependent variability in INP concentrations, indicative of boundary layer stratification and contributions from both local and transported aerosol sources. All resulting TBSINP data are publicly available via the ARM Data Center, and researchers may request PUFIN for future TBS campaigns or access archived filters for additional analyses. Looking forward, routine PUFIN deployments can be used to enhance understanding of the vertical distribution and seasonal variability of INPs, enabling improved representation of aerosol-cloud interactions in Earth system models and advancing predictive capabilities for weather and climate.