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In the western US and similar topographic regions across the world, precipitation in the mountains is crucial to local and downstream freshwater supplies. Atmospheric aerosols can impact clouds and precipitation by acting as cloud condensation nuclei (CCN) and ice-nucleating particles (INPs). Previous studies suggest that there is increased aerosol variability in these regions due to their complex terrain, but none of these studies have quantified the extent of this variability. In the fall of 2021, Handix Scientific contributed to the Surface Atmosphere Integrated Field Laboratory (SAIL), funded by the US Department of Energy (DOE) and situated in the East River watershed (ERW; Colorado, USA), by deploying SAIL-Net, a novel network of six aerosol measurement nodes spanning the horizontal and vertical domains of SAIL. The ERW is a topographically diverse region, meaning individual measurement sites can miss important observations of aerosol–cloud interactions. Each measurement node included a small particle counter (the Portable Optical Particle Spectrometer – POPS), a miniature CCN counter (CloudPuck), and a filter sampler (the Time-Resolved Aerosol Particle Sampler – TRAPS) for INP analysis. SAIL-Net studied the spatiotemporal variability in aerosols and the usefulness of dense measurement networks in complex terrain. After the project's completion in the summer of 2023, we analyzed the data to explore these topics. We found increased variability compared to a similar study over flat land. This variability was correlated with the elevation of the sites, and the extent of the variability changed seasonally. These data and analyses serve as a valuable resource for continued research into the role of aerosols in the hydrologic cycle and as the foundation for designing measurement networks in complex terrain. [ABSTRACT FROM AUTHOR]

The third phase of the Fifth International Ice Nucleation Workshop (FIN-03) was conducted at the Storm Peak Laboratory in Steamboat Springs, Colorado, in September 2015 to facilitate the intercomparison of instruments measuring ice-nucleating particles (INPs) in the field. Instruments included two online and four offline measurement systems for INPs, which are a subset of those utilized in the laboratory study that comprised the second phase of FIN (FIN-02). The composition of the total aerosols was characterized using the Particle Analysis by Laser Mass Spectrometry (PALMS) and Wideband Integrated Bioaerosol Sensor (WIBS) instruments, and aerosol size distributions were measured by a laser aerosol spectrometer (LAS). The dominant total particle compositions present during FIN-03 were composed of sulfates, organic compounds, and nitrates, as well as particles derived from biomass burning. Mineral-dust-containing particles were ubiquitous throughout and represented 67 % of supermicron particles. Total WIBS fluorescing particle concentrations for particles with diameters of > 0.5 µm were 0.04 ± 0.02 cm−3 (0.1 cm−3 highest; 0.02 cm−3 lowest), typical of the warm season in this region and representing ≈ 9 % of all particles in this size range as a campaign average. The primary focus of FIN-03 was the measurement of INP concentrations via immersion freezing at temperatures > - 33 °C. Additionally, some measurements were made in the deposition nucleation regime at these same temperatures, representing one of the first efforts to include both mechanisms within a field campaign. INP concentrations via immersion freezing agreed within factors ranging from nearly 1 to 5 times on average between matched (time and temperature) measurements, and disagreements only rarely exceeded 1 order of magnitude for sampling times coordinated to within 3 h. Comparisons were restricted to temperatures lower than - 15 °C due to the limits of detection related to sample volumes and very low INP concentrations. Outliers of up to 2 orders of magnitude occurred between - 25 and - 18 °C; a better agreement was seen at higher and lower temperatures. Although the 5–10 factor agreement of INP measurements found in FIN-03 aligned with the results of the FIN-02 laboratory comparison phase, giving confidence in progress of this measurement field, this level of agreement still equates to temperature uncertainties of 3.5 to 5 °C that may not be sufficient for numerical cloud modeling applications that utilize INP information. INP activity in the immersion-freezing mode was generally found to be an order of magnitude or more, making it more efficient than in the deposition regime at 95 %–99 % water relative humidity, although this limited data set should be augmented in future efforts. To contextualize the study results, an assessment was made of the composition of INPs during the late-summer to early-fall period of this study inferred through comparison to existing ice nucleation parameterizations and through measurement of the influence of thermal and organic carbon digestion treatments on immersion-freezing ice nucleation activity. Consistent with other studies in continental regions, biological INPs dominated at temperatures of > - 20 °C and sometimes colder, while arable dust-like or other organic-influenced INPs were inferred to dominate below - 20 °C. [ABSTRACT FROM AUTHOR]