Here we report the ice nucleating temperatures of marine aerosols sampled in the subarctic Atlantic Ocean during a phytoplankton bloom. Ice nucleation measurements were conducted on primary aerosol samples and phytoplankton isolated from seawater samples. Primary marine aerosol samples produced by a specialized aerosol generator (the Sea Sweep) catalyzed droplet freezing at temperatures between −33.4 °C and − 24.5 °C, with a mean freezing temperature of −28.5 °C, which was significantly warmer than the homogeneous freezing temperature of pure water in the atmosphere (−36 °C). Following a storm‐induced deep mixing event, ice nucleation activity was enhanced by two metrics: (1) the fraction of aerosols acting as ice nucleating particles (INPs) and (2) the nucleating temperatures, which were the warmest observed throughout the project. Seawater samples were collected from the ocean's surface and phytoplankton groups, including Synechococcus, picoeukaryotes, and nanoeukaryotes, were isolated into sodium chloride sheath fluid solution using a cell‐sorting flow cytometer. Marine aerosol containing Synechococcus, picoeukaryotes, and nanoeukaryotes serves as INP at temperatures significantly warmer than the homogeneous freezing temperature of pure water in the atmosphere. Samples containing whole organisms in 30 g L−1 NaCl had freezing temperatures between −33.8 and − 31.1 °C. Dilution of samples to representative atmospheric aerosol salt concentrations (as low as 3.75 g L−1 NaCl) raised freezing temperatures to as high as −22.1 °C. It follows that marine aerosols containing phytoplankton may have widespread influence on marine ice nucleation events by facilitating ice nucleation.
Abstract. Ice nucleating particles (INPs) initiate primary ice formation in Arctic mixed-phase clouds, altering cloud radiative properties and modulating precipitation. For atmospheric INPs, the complexity of their spatiotemporal variations, heterogeneous sources and evolution via intricate atmospheric interactions challenge the understanding of their impact on microphysical processes in Arctic mixed-phase clouds and induce an uncertain representation in climate models. In this work, we performed a comprehensive analysis of atmospheric aerosols at the Arctic coastal site in Ny-Ålesund (Svalbard, Norway) from October to November 2019, including their ice nucleation ability, physicochemical properties and potential sources. Overall, INP concentrations during the observation season were approximately up to three orders of magnitude lower compared to the global average, with several samples showing degradation of INP concentrations after heat treatment, implying the presence of proteinaceous INPs. Particle fluorescence was substantially associated with INP concentrations at warmer ice nucleation temperatures, indicating that in the far-reaching Arctic, aerosols of biogenic origin throughout the snow- and ice-free season may serve as important INP sources. In addition, case studies revealed the links between elevated INP concentrations to heat-lability, fluorescence, high wind speeds originating from the ocean, augmented concentration of coarse-mode particles and abundant organics. Backward trajectory analysis demonstrated a potential connection between high-latitude dust sources and high INP concentrations, while prolonged air mass history over the ice pack was identified for most scant INP cases. The combination of the above analyses demonstrates the abundance, physicochemical properties and potential sources of INPs in the Arctic are highly variable despite its remote location.
<p>Ice-nucleating particles (INPs) are aerosol particles that catalyze the heterogeneous formation of ice crystals under ice supersaturation conditions. These INPs can change cloud characteristics on wide spatiotemporal scales, including albedo and radiative effects, as well as precipitation types and amounts, thus affecting both weather and climate. However, INP measurements with reasonable temporal resolution have been challenging in terms of both technology and logistics in our research community. Here we present preliminary results of our recent six-month effort from the Eastern North Atlantic (ENA) field campaign to advance the research and explore remote operation of the plug-and-play Portable Ice Nucleation Experiment (PINE) chamber to semi-autonomously measure marine boundary layer INP concentrations. In this campaign we deployed our PINE chamber at the U.S. Department of Energy Atmospheric Radiation Measurement (DOE ARM) ENA site on Graciosa Island, Azores (39&#176; 5&#8242; 29.76&#8243; N, 28&#176; 1&#8242; 32.52&#8243; W). The PINE chamber has been continuously operated since October 2020 with supervision and periodic remote maintenance by scientists in West Texas. The INP measurements were conducted at mixed-phase cloud conditions at temperatures between -14&#176;C and -33&#176;C. These measurements, along with other aerosol particle and meteorological measurements made by a suite of instruments collocated at the DOE ARM site, give unique insights on the response of INP concentrations to local and mesoscale dynamics and thermodynamic processes. This study provides the first remote and continuous INP measurements over two meteorological seasons made in the ENA region within the marine boundary layer, giving insights into an area with prominent marine influences on aerosol populations. Graciosa Island is a small island (only 61 km<sup>2</sup>) surrounded by oligotrophic oceans, and these measurements were made during the most biologically productive time of year for phytoplankton in the surrounding ocean waters. The long-term and continuous nature of these measurements allows a unique comparison of marine biological productivity, using satellite-derived chlorophyll a as a proxy for biomass, and INP concentrations. The median INP concentrations at -25 &#176;C and -30 &#176;C were around 4 INP L<sup>-1</sup> and 27 INP L<sup>-1 </sup>respectively. Our preliminary data suggest that INP concentrations measured by the PINE chamber at the ENA site are comparable to other studies at locations with primarily marine INPs. More details will be offered in our presentation.</p>
Atmospheric ice-nucleating particles (INPs) from mineral dust and non-proteinaceous biological sources can influence cloud formation, precipitation, and Earth's radiation budget due to their efficient freezing abilities. The ambient aerosol particles from these sources are abundant with ambient concentrations exceeding a few μg mˆ-3 for each type. Thus, the characterization of INPs and aerosol particles from these sources is important. We typically characterize their specific surface area (SSA), which is the primary variable to estimate their ice-nucleation active surface site density, using a sorbate gas, such as nitrogen. However, it is still uncertain how these particles interact with water vapor under subzero temperatures. To fill this gap, we used the 3Flex instrument (Micromeritics Instrument Corp.) with multiple sorbates to comprehensively characterize the nanoscale surface structure, pore size distribution, and accessibility to water molecules of a commercially available model proxy of mineral dust (illite NX) and cellulose materials. To date, we have completed more than 60 physisorption 3Flex experiments with various sorbates, such as CO2, H2O, Kr, and N2, for each sorbent. In particular, we examined SSA by water vapor sorption at temperatures relevant to atmospheric heterogeneous freezing (˜0 to -20 °C). We will present our results as physisorption isotherms. In addition, our preliminary results of temperature-dependent SSA observed for micro-and nano-crystalline cellulose materials as well as illite NX will be discussed. Our preliminary result suggests that the SSA of illite NX is less temperaturedependent compared to the cellulose materials, which may be potentially swelling while interacting with water. Therefore, illite NX may be suitable for an INP test proxy.
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