Sonia M. Kreidenweis

The NASA airborne Arctic Radiation-Cloud-aerosol-Surface-Interaction Experiment (ARCSIX) collected a unique data set providing a near-simultaneous characterization of radiative fluxes, surface, cloud, and aerosol particle properties to address science questions on the surface radiation budget, the processes governing the cloud lifecycle, atmospheric composition, and the interactions between the surface and atmosphere. The overarching goal of ARCSIX was to quantify the contributions of surface, clouds, aerosol particles, and precipitation to summer sea ice melt. ARCSIX consisted of two deployments in 2024 (Spring: 2024-05-28 through 2024-06-13 and Summer: 2024-07-25 through 2024-08-15) to capture pre- and post-melt conditions. ARCSIX provided coordinated remote sensing and in situ sampling using three aircraft in a high-flyer/low-flyer configuration. The NASA G-III served as the high-flying remote sensing platform with two lower flying in situ and near-target remote sensor observing platforms, NASA P-3B and SPEC Inc. Learjet. ARCSIX data are well-suited to improve satellite remote sensing capabilities in the Arctic. ARCSIX included an array of sea ice mass balance buoys deployed in the Lincoln Sea that were regularly overflown during the campaign. ARCSIX research flights spanned the Baffin Bay, Lincoln Sea, west and north of the Canadian Archipelago, and the Greenland north and northeast coasts. During the spring deployment, 19 research flights took place covering 114 flight hours: 10 flights and 68 hours by the P-3B and nine flights and 46 hours by the G-III. During summer, 24 research flights covered 136 flight hours: nine flights and 75 hours by the P-3B, five flights and 26 hours by the G-III, and 10 flights and 35 hours by the Learjet. A total of 13 coordinated flights with 2+ aircraft were carried out. This paper describes the ARCSIX flight strategy, instrumentation, and data set access, and usage details. ARCSIX data are publicly available at https://doi.org/10.5067/SUBORBITAL/ARCSIX/DATA001.

Bioaerosols have important impacts on human health and potentially on weather and climate through aerosol–cloud interactions. Reciprocally, weather systems can have a large impact on bioaerosols both indirectly through ecosystem-level influences and by playing a more direct role in bioaerosol emission, deposition, and transport. In this work, we discuss the design and initial findings of the Bioaerosols and Convective Storms (BACS) field campaigns, a project targeting the interplay of these two effects. Two BACS field campaigns were conducted in the springs of 2022 and 2023, examining the dynamics of speciated and cloud-relevant aerosol and, especially, bioaerosol observations surrounding precipitation events and cold pool outflows from convective storms. A multifaceted deployment strategy was used, leveraging a combination of online and offline measurements of aerosol and bioaerosol distributions, cloud-relevant properties, and chemical tracers in the context of atmospheric state measurements. The observational strategy included measurements at ground level, a 9-m flux tower, and simultaneous stacked column and profiling multirotor drone measurements and radiosonde launches. Aerosol and bioaerosol responses to precipitation and cold pool events are examined within this manuscript through several case studies highlighting that similar events can produce very different aerosol responses. Reasons for this variability are hypothesized and discussed in the context of our campaign data, and targets for future investigations are suggested. Significance Statement: This work is motivated by understanding a phenomenon with direct human impacts; storm lofting and transport of bioaerosols are known to cause health impacts such as “thunderstorm asthma,” while the same sources of bioaerosols may additionally impact storm evolution. This work describes an extensive campaign dataset, showcasing two cases to highlight how the dataset can be used to probe these questions and raising some of the crucial scientific questions requiring further investigation.

Biological aerosol particles influence atmospheric processes, including cloud ice nucleation through action as ice-nucleating particles (INPs). Their abundance is altered by convective storm processes such as precipitation and cold pools. To improve the understanding of bioaerosol characteristics, sources, and variability during convective storms, we conducted two intensive field campaigns in May–June 2022 and 2023 at a semiarid grassland area in Colorado. The two seasons had contrasting environmental conditions, with exceptionally dry conditions in 2022 and unusually wet conditions in 2023. Bioaerosols were characterized using fluorescence and chemical tracers, while INPs were measured in air (before, during, and after rainfall), precipitation water, and terrestrial source samples; these measurements were aligned with disdrometer- and drone-based observations. Peak fluorescent particle concentrations correlated significantly with cold pool strength (rs=0.81, p

Ice nucleating particles (INPs) play a critical role in determining cloud phase, lifetime, and radiative properties in polar regions, yet their sources, composition, and variability remain poorly constrained. The Arctic and Antarctic present fundamentally different environmental settings, with contrasting land-ocean distributions, biological productivity, sea-ice regimes, and anthropogenic influence, offering a natural laboratory to examine how these factors shape polar INP populations.Here, we synthesize recent in situ observations of INP concentrations and properties from ground-based and shipborne platforms across both polar regions, spanning multiple seasons and temperature regimes relevant to mixed-phase cloud formation. Arctic INPs are frequently influenced by terrestrial and sea-ice-related biological sources, and long-range transport, leading to pronounced seasonal variability. In contrast, Antarctic INP populations are typically lower in concentration and more strongly linked to a combination of coastal marine and inorganic sources from over the ice sheet, with concentrations predominantly existing at colder activation temperatures. We highlight emerging evidence for the importance of primary biological aerosols, sea-ice biogeochemistry, and boundary layer processes in regulating Antarctic INPs, while underscoring the role of surface heterogeneity and transport pathways in the Arctic. Differences in vertical distributions and coupling to clouds further suggest divergent impacts on mixed-phase cloud persistence and radiative feedbacks between the two poles.These inter-polar contrasts challenge the common practice of treating polar INPs as a uniform class in models and underscore the need for regionally and process-informed representations. Improving constraints on polar INPs is essential for reducing uncertainties in cloud-phase feedbacks and future climate projections in both hemispheres.

Ice nucleating particles (INPs) influence cloud properties, precipitation, and radiative forcing, yet knowledge regarding their sources and characteristics remains incomplete, especially in polluted Arctic and subarctic environments. This study investigates the size and composition of INPs during the Alaskan Layered Pollution And Chemical Analysis (ALPACA) campaign, conducted in Fairbanks from January 17 to February 25, 2022. Fairbanks is a unique location situated in a valley with extreme cold, frequent temperature inversions, and persistent pollution during winter, conditions that favor ice fog formation and make local cloud microphysics highly sensitive to INPs. We report INP data from online measurements using a continuous flow diffusion chamber and offline filter and size-resolved impactor samples. Interpretation of the observations was supported by contextual aerosol size and composition data. Our findings show that while the aerosol population was dominated by submicron particles by number and mass, INP activity was concentrated in the supermicron (1.21-12 µm) range. INPs were primarily composed of heat-labile organic material across all size ranges and freezing temperatures, with over 90% of INPs at -15°C and -20°C identified as proteinaceous or biological in origin. Local sources, such as lichen and road gravel, were likely contributors to the observed INP population. Compared to other urban and Arctic sites, Fairbanks exhibited higher INP concentrations at lower temperatures and lower concentrations at warmer temperatures. These results provide new insight into the nature of INPs in subarctic, polluted-urban regions and emphasize the importance of particle size and local emissions in determining INP activity and abundance.

Atmospheric ice-nucleating particles (INPs) significantly influence cloud microphysics and aerosol-cloud interactions. Understanding INPs in mountain regions is important for predicting impacts on regional clouds and precipitation. In this study, we conducted comprehensive measurements of immersion-freezing INPs at Mt. Crested Butte in the Rocky Mountains from September 2021 to June 2023 as part of the Surface Atmosphere Integrated Field Laboratory (SAIL) campaign. The average number concentration of INPs active at −20 °C was 2 L−1, with distinct seasonal variation characterized by high summer concentrations and low winter concentrations. Aerosol sources were resolved, and INP concentrations were correlated with a coarse dust aerosol type, which dominates PM10 in this region. Calculating IN active surface site densities (ns) further supporting the primary contribution from coarse dust to INPs. Treatment with H2O2 indicated substantial contributions (91 % on average) from organic INPs across all activation temperatures, suggesting that supermicron organic-containing soil dust dominates the INPs in this region. Heat-labile INPs, likely biological in origin, were identified as dominant at >-15 °C through heat treatment of samples and showed significantly lower contributions in winter (∼ 96 % reduction). Parameterizations based on ns for the INPs observed in this mountainous region were developed, which effectively reproduced measured INP concentrations, particularly when accounting for seasonal differences. This study provides the first long-term, comprehensive characterization of INPs for the Upper Colorado River Basin region and offers a parameterization potentially useful for predicting INPs in other remote continental regions.

Thunderstorms and precipitation can alter bioaerosol properties and concentrations, potentially enhancing their impacts on public health and cloud microphysics.