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This study presents a comprehensive investigation of ice -nucleating particles (INPs) in the surface materials and aerosol particles from U.S. cattle feeding facilities. Using a modern suite of online and offline aerosol particle characterization instruments, we conducted a three-year field survey (2016-2019), Aerosol Interaction and Dynamics in the Atmosphere (AIDA) cloud chamber experiments, and ice crystal residual (ICR) analyses for the feedlot sample. Our results showed unique supermicron size dominance in the feedlot INPs with a high concentration of INPs (several hundred and thousand INPs L-1 at -20 °C and -25 °C, respectively). Thus, agricultural fields, especially animal feeding facilities, represent important INP sources if these particles rise to sufficient height in the atmosphere. New data on the ice nucleation (IN) properties of agricultural dust at heterogeneous freezing temperatures (Ts > -29 °C) were generated, providing statistical context. Overall, we successfully characterized physical, chemical, and biological properties of aerosol particles found at a cattle feedlot, thereby finding their unique heat-tolerant nature. The relationship between these measured properties and atmospheric IN parameterization relevant to mixed-phase clouds is discussed. Our INP parameterization and ICR characterization are meaningful for improved understanding of INP emission and cloud microphysical processes in the supermicron-particle laden region. These unique INPs may directly influence the lifetime of supercooled clouds in a unique manner for this region. An application of our IN parameterization is crucial to explore INP relations to supercooled cloud properties over such a predominant agricultural area. [ABSTRACT FROM AUTHOR]

The current inadequate understanding of ice nucleating particle (INP) sources in the Arctic region affects the uncertainty in global radiative budgets and in regional climate predictions. In this study, we present atmospheric INP concentrations by offline analyses on samples collected at ground level in Ny-Ålesund (Svalbard), in spring and summer 2018. The ice nucleation properties of the samples were characterized by means of two offline instruments: the Dynamic Filter Processing Chamber (DFPC), detecting condensation freezing INPs, and the West Texas Cryogenic Refrigerator Applied to Freezing Test system (WT-CRAFT), measuring INPs by immersion freezing. Both measurements agreed within an order of magnitude although with some notable offset. INP concentration measured by DFPC ranged 33-185 (median 88), 5-107 (50) and 3-66 (20) m−3, for T = −22, −18 and −15 °C, respectively, while at the same activation temperatures WT-CRAFT measured 3-199 (26), 1-34 (6) and 1-4 (2) m−3, with an offset apparently dependent on the INP activation temperature. This observation may indicate a different sensitivity of Arctic INPs to different ice nucleation modes, even though a contribution from measurement and/or sampling uncertainties cannot be ruled out. An increase in the coarse INP fraction was observed from spring to summer, particularly at the warmest temperature (up to ~ 70 % at −15 °C). This suggests a non-negligible contribution from local sources of biogenic aerosol particles. This conclusion is also supported by the INP temperature spectra, showing ice-forming activity at temperatures higher than −15 °C. Contrary to recent works (e.g., INP measurements from Ny-Ålesund in 2012), our results do not show a sharp spring-to-summer increase of the INP concentration, with distinct behaviors for particles active in different temperature ranges. This likely indicates that the inter-annual variability of conditions affecting the INP emission by local sources may be wider than previously considered and suggests a complex interplay between INP sources. This demonstrate the necessity of further data coverage. Analysis of INP concentrations, active site density, low-travelling back-trajectories (< 500 m) and ground conditions during the air mass passage suggest that the summertime INP population may be contributed both by terrestrial and marine sources. Air masses in contact with snow-free land had higher INP concentrations, likely reflecting the higher nucleation ability of terrestrial particles. Outside the major terrestrial inputs, the INP population was likely regulated by marine INPs emitted from the sea surface. Evidence of the relation between background INP concentration and the patterns of marine biological activity have been provided by investigating its spatio-temporal correlation with satellite retrieved Chlorophyll-a fields and by the Concentration Weighted Trajectory (CWT) model. The results suggest that sources of INPs may be located both in the seawaters surrounding the Svalbard archipelago and/or as far as Greenland and Iceland. [ABSTRACT FROM AUTHOR]

Ice nucleating particles (INP) have a large impact on the climate-relevant properties of clouds over the oceans. Studies have shown that sea spray aerosols (SSA), produced upon bursting of bubbles at the ocean surface, can be an important source of marine INP, particularly during periods of enhanced biological productivity. Recent mesocosm experiments using natural seawater spiked with nutrients have revealed that marine INP are derived from two separate classes of organic matter in SSA. Despite this finding, existing parameterizations for marine INP abundance are based solely on single variables such as total organic carbon (TOC) or SSA surface area, which may mask specific trends in the separate classes of INPs. The goal of this paper is to improve the understanding of the connection between ocean biology and marine INP abundance by reporting results from a field study and proposing a new parameterization of marine INP that accounts for the two associated classes of organic matter. The PEACETIME cruise took place from May 10 to June 10, 2017 in the Mediterranean Sea. Throughout the cruise, INP concentrations in the surface microlayer (SML) and in SSA produced using a plunging aquarium apparatus were continuously monitored while surface seawater (SSW) and SML biological properties were measured in parallel. The organic content of artificially generated SSA was also evaluated. A dust wet deposition event that occurred during the cruise increased the INP concentrations measured in the SML by an order of magnitude, in line with increases of iron in the SML and bacterial abundances. Increases of INPs in marine SSA (INP[sub SSA]) were not observed before a delay of three days compared to increases in the SML, and are likely a result of a strong influence of bulk SSW INP for the temperatures investigated (T=-18°C for SSA, T=-16°C for SSW). Results confirmed that INPSSA are divided into two classes depending on their associated organic matter. Here we find that warm (T ≥ -22C) INPSSA concentrations are correlated with water soluble organic matter in the SSA, but also to SSW parameters (POCSSW INPSSW,-16C) while cold INPSSA (T < -22C) are correlated with SSA water-insoluble organic carbon (WIOC) and SML dissolved organic carbon (DOC) concentration. A relationship was also found between cold INPSSA and SSW microphytoplankton cell abundances, indicating that these species might be at the origin of water insoluble organic matter with surfactant properties and specific IN properties. Using these results, we propose a two-component parameterization for the abundance of INP in marine SSA and compare it with previous single-component models based on SSA surface area and TOC content. This new, two-component parameterization should improve attempts to incorporate marine INP emissions into numerical models. Future studies will be conducted to confirm if our parameterization can be extended to regions of higher biological productivity, such as the Southern Ocean. [ABSTRACT FROM AUTHOR]

This paper addresses the problem of the large discrepancies between ice crystal concentrations in clouds and the number of ice nuclei in nearby clear air reported in published papers. Such discrepancies cannot always be explained, even by taking into account both primary and secondary ice formation processes. A laboratory experiment was performed in a cylindrical column placed in a cold room at atmospheric pressure and temperature in the −12° to −14°C range. Supercooled droplets were nucleated in the column, in the absence of aerosol ice nuclei, by injecting ice crystals generated outside in a small syringe. A rapid increase in the ice crystal concentration was observed in the absence of any known ice multiplication. The ratio between the mean number of ice crystals in the column, after complete droplet vaporization, and the number of ice crystals introduced in the column was about 10:1. The presence of small ice crystals (introduced at the top of the column) in the unstable system (supercooled droplets) appears to trigger the transformation in the whole supercooled liquid cloud. A possible explanation could be that the rapidly evaporating droplets cool sufficiently to determine a homogeneous nucleation. [ABSTRACT FROM AUTHOR]