Is the ocean enough? – Indications towards the origin of Ice Nucleating Particles from May to July in the Arctic

2021 ◽  
Author(s):  
Markus Hartmann ◽  
Xianda Gong ◽  
Simonas Kecorius ◽  
Manuela van Pinxteren ◽  
Teresa Vogl ◽  
...  
Keyword(s):  
Radiative Forcing ◽  
Climate Models ◽  
Sea Water ◽  
Sea Surface ◽  
Radiative Properties ◽  
The Arctic ◽  
Surface Microlayer ◽  
German Research Foundation ◽  
Fog Water ◽  
Sea Surface Microlayer

<p>Low-level mixed-phase clouds are important factors influencing the energy budget of the Arctic boundary layer. The radiative properties of these clouds are determined by their microphysical properties. Aerosol particles that act as Ice Nucleating Particles (INP), impact the primary ice formation inside clouds and thereby affect cloud lifetime, albedo and precipitation formation. The sources of INP in the Arctic, their properties, nature and concentration are poorly understood which results in substantial uncertainties radiative forcing estimates in climate models.</p><p>Here, we present ship-based measurements of INP in different environmental compartments (air, sea surface microlayer, bulk sea water, fog water) in the Arctic. From May to July 2017 the PASCAL field campaign took place around and north of Svalbard (up to 84°N, between 0° and 35°E) onboard the RV Polarstern. INP concentrations were measured online with the SPIN instrument (Spectrometer for Ice Nuclei, DMT) and offline through filter sampling and analysis with freezing array techniques. We assess possible connections between the INP in the sea water and air, as well as between INP in the fog water and air through a closure study.</p><p>Generally, INP concentrations in the Arctic were found to be lower than in mid-latitudes with the exception of elevated INP concentrations at temperatures above -15°C and below -30°C. We attribute elevated INP concentrations to the presence of biogenic, probably proteinaceous INP, at the warmer, and to the presence of mineral dust at colder temperatures, respectively. The closure studies revealed that:<br>a) all INP in the air are activated to fog droplets, and <br>b) the INP concentration in seawater alone cannot explain INP concentration in air without a substantial enrichment of INP (factor 10<sup>4</sup> to 10<sup>5</sup>) during the transfer of INP from the sea surface to the atmosphere. <br>We present indications for a local, marine source of INP from a case study looking at the period when atmospheric INP concentrations were highest in the temperature range above -15°C. These findings highlight the need for future studies to assess especially the production mechanisms and source strength for Arctic INP.</p><p><em>We gratefully acknowledge the funding by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) – Projektnummer 268020496 – TRR 172, within the Transregional Collaborative Research Center “ArctiC Amplification: Climate Relevant Atmospheric and SurfaCe Processes, and Feedback Mechanisms (AC)<sup>3</sup></em></p>

scholarly journals New insights into aerosol and climate in the Arctic

2018 ◽  
Author(s):  
Jonathan P. D. Abbatt ◽  
W. Richard Leaitch ◽  
Amir A. Aliabadi ◽  
Alan K. Bertram ◽  
Jean-Pierre Blanchet ◽  
...  
Keyword(s):  
Long Range ◽  
Mineral Dust ◽  
Sea Surface ◽  
The Arctic ◽  
Long Range Transport ◽  
Surface Microlayer ◽  
Biogeochemical Models ◽  
Sea Surface Microlayer ◽  
Range Transport ◽  
Warming World

Abstract. Motivated by the need to predict how the Arctic atmosphere will change in a warming world, this article summarizes recent advances made by the research consortium NETCARE (Network on Climate and Aerosols: Addressing Key Uncertainties in Remote Canadian Environments) that contribute to our fundamental understanding of Arctic aerosol particles as they relate to climate forcing. The overall goal of NETCARE research has been to use an interdisciplinary approach encompassing extensive field observations and a range of chemical transport, earth system, and biogeochemical models. Several major findings and advances have emerged from NETCARE since its formation in 2013 . (1) Unexpectedly high summertime dimethyl sulfide (DMS) levels were identified in ocean water and the overlying atmosphere in the Canadian Arctic Archipelago (CAA). Furthermore, melt ponds, which are widely prevalent, were identified as an important DMS source. (2) Evidence was found of widespread particle nucleation and growth in the marine boundary layer in the CAA in the summertime. DMS-oxidation-driven nucleation is facilitated by the presence of atmospheric ammonia arising from sea bird colony emissions, and potentially also from coastal regions, tundra, and biomass burning. Via accumulation of secondary organic material (SOA), a significant fraction of the new particles grow to sizes that are active in cloud droplet formation. Although the gaseous precursors to Arctic marine SOA remain poorly defined, the measured levels of common continental SOA precursors (isoprene and monoterpenes) were low, whereas elevated mixing ratios of oxygenated volatile organic compounds were inferred to arise via processes involving the sea surface microlayer. (3) The variability in the vertical distribution of black carbon (BC) under both springtime Arctic haze and more pristine summertime aerosol conditions was observed. Measured particle size distributions and mixing states were used to constrain, for the first time, calculations of aerosol–climate interactions under Arctic conditions. Aircraft- and ground-based measurements were used to better establish the BC source regions that supply the Arctic via long-range transport mechanisms. (4) Measurements of ice nucleating particles (INPs) in the Arctic indicate that a major source of these particles is mineral dust, likely derived from local sources in the summer and long-range transport in the spring. In addition, INPs are abundant in the sea surface microlayer in the Arctic, and possibly play a role in ice nucleation in the atmosphere when mineral dust concentrations are low. (5) Amongst multiple aerosol components, BC was observed to have the smallest effective deposition velocities to high Arctic snow.

scholarly journals Water-Soluble Organic Composition of the Arctic Sea Surface Microlayer and Association with Ice Nucleation Ability

2018 ◽  
Vol 52 (4) ◽  
pp. 1817-1826 ◽  
Author(s):  
Rosie J. Chance ◽  
Jacqueline F. Hamilton ◽  
Lucy J. Carpenter ◽  
Sina C. Hackenberg ◽  
Stephen J. Andrews ◽  
...  
Keyword(s):  
Ice Nucleation ◽  
Water Soluble ◽  
Sea Surface ◽  
The Arctic ◽  
Surface Microlayer ◽  
Organic Composition ◽  
Sea Surface Microlayer ◽  
Arctic Sea

scholarly journals Overview paper: New insights into aerosol and climate in the Arctic

2019 ◽  
Vol 19 (4) ◽  
pp. 2527-2560 ◽  
Author(s):  
Jonathan P. D. Abbatt ◽  
W. Richard Leaitch ◽  
Amir A. Aliabadi ◽  
Allan K. Bertram ◽  
Jean-Pierre Blanchet ◽  
...  
Keyword(s):  
Long Range ◽  
Mineral Dust ◽  
Sea Surface ◽  
The Arctic ◽  
Long Range Transport ◽  
Surface Microlayer ◽  
Biogeochemical Models ◽  
Sea Surface Microlayer ◽  
Range Transport ◽  
Warming World

Abstract. Motivated by the need to predict how the Arctic atmosphere will change in a warming world, this article summarizes recent advances made by the research consortium NETCARE (Network on Climate and Aerosols: Addressing Key Uncertainties in Remote Canadian Environments) that contribute to our fundamental understanding of Arctic aerosol particles as they relate to climate forcing. The overall goal of NETCARE research has been to use an interdisciplinary approach encompassing extensive field observations and a range of chemical transport, earth system, and biogeochemical models. Several major findings and advances have emerged from NETCARE since its formation in 2013. (1) Unexpectedly high summertime dimethyl sulfide (DMS) levels were identified in ocean water (up to 75 nM) and the overlying atmosphere (up to 1 ppbv) in the Canadian Arctic Archipelago (CAA). Furthermore, melt ponds, which are widely prevalent, were identified as an important DMS source (with DMS concentrations of up to 6 nM and a potential contribution to atmospheric DMS of 20 % in the study area). (2) Evidence of widespread particle nucleation and growth in the marine boundary layer was found in the CAA in the summertime, with these events observed on 41 % of days in a 2016 cruise. As well, at Alert, Nunavut, particles that are newly formed and grown under conditions of minimal anthropogenic influence during the months of July and August are estimated to contribute 20 % to 80 % of the 30–50 nm particle number density. DMS-oxidation-driven nucleation is facilitated by the presence of atmospheric ammonia arising from seabird-colony emissions, and potentially also from coastal regions, tundra, and biomass burning. Via accumulation of secondary organic aerosol (SOA), a significant fraction of the new particles grow to sizes that are active in cloud droplet formation. Although the gaseous precursors to Arctic marine SOA remain poorly defined, the measured levels of common continental SOA precursors (isoprene and monoterpenes) were low, whereas elevated mixing ratios of oxygenated volatile organic compounds (OVOCs) were inferred to arise via processes involving the sea surface microlayer. (3) The variability in the vertical distribution of black carbon (BC) under both springtime Arctic haze and more pristine summertime aerosol conditions was observed. Measured particle size distributions and mixing states were used to constrain, for the first time, calculations of aerosol–climate interactions under Arctic conditions. Aircraft- and ground-based measurements were used to better establish the BC source regions that supply the Arctic via long-range transport mechanisms, with evidence for a dominant springtime contribution from eastern and southern Asia to the middle troposphere, and a major contribution from northern Asia to the surface. (4) Measurements of ice nucleating particles (INPs) in the Arctic indicate that a major source of these particles is mineral dust, likely derived from local sources in the summer and long-range transport in the spring. In addition, INPs are abundant in the sea surface microlayer in the Arctic, and possibly play a role in ice nucleation in the atmosphere when mineral dust concentrations are low. (5) Amongst multiple aerosol components, BC was observed to have the smallest effective deposition velocities to high Arctic snow (0.03 cm s−1).

scholarly journals The ice-nucleating activity of Arctic sea surface microlayer samples and marine algal cultures

2020 ◽  
Vol 20 (18) ◽  
pp. 11089-11117 ◽  
Author(s):  
Luisa Ickes ◽  
Grace C. E. Porter ◽  
Robert Wagner ◽  
Michael P. Adams ◽  
Sascha Bierbauer ◽  
...  
Keyword(s):  
Ice Nucleation ◽  
Sea Surface ◽  
The Arctic ◽  
Sea Spray ◽  
Surface Microlayer ◽  
Phytoplankton Species ◽  
Sea Surface Microlayer ◽  
Nucleation Activity ◽  
Ice Nucleation Activity ◽  
Algal Cultures

Abstract. In recent years, sea spray as well as the biological material it contains has received increased attention as a source of ice-nucleating particles (INPs). Such INPs may play a role in remote marine regions, where other sources of INPs are scarce or absent. In the Arctic, these INPs can influence water–ice partitioning in low-level clouds and thereby the cloud lifetime, with consequences for the surface energy budget, sea ice formation and melt, and climate. Marine aerosol is of a diverse nature, so identifying sources of INPs is challenging. One fraction of marine bioaerosol (phytoplankton and their exudates) has been a particular focus of marine INP research. In our study we attempt to address three main questions. Firstly, we compare the ice-nucleating ability of two common phytoplankton species with Arctic seawater microlayer samples using the same instrumentation to see if these phytoplankton species produce ice-nucleating material with sufficient activity to account for the ice nucleation observed in Arctic microlayer samples. We present the first measurements of the ice-nucleating ability of two predominant phytoplankton species: Melosira arctica, a common Arctic diatom species, and Skeletonema marinoi, a ubiquitous diatom species across oceans worldwide. To determine the potential effect of nutrient conditions and characteristics of the algal culture, such as the amount of organic carbon associated with algal cells, on the ice nucleation activity, Skeletonema marinoi was grown under different nutrient regimes. From comparison of the ice nucleation data of the algal cultures to those obtained from a range of sea surface microlayer (SML) samples obtained during three different field expeditions to the Arctic (ACCACIA, NETCARE, and ASCOS), we found that they were not as ice active as the investigated microlayer samples, although these diatoms do produce ice-nucleating material. Secondly, to improve our understanding of local Arctic marine sources as atmospheric INPs we applied two aerosolization techniques to analyse the ice-nucleating ability of aerosolized microlayer and algal samples. The aerosols were generated either by direct nebulization of the undiluted bulk solutions or by the addition of the samples to a sea spray simulation chamber filled with artificial seawater. The latter method generates aerosol particles using a plunging jet to mimic the process of oceanic wave breaking. We observed that the aerosols produced using this approach can be ice active, indicating that the ice-nucleating material in seawater can indeed transfer to the aerosol phase. Thirdly, we attempted to measure ice nucleation activity across the entire temperature range relevant for mixed-phase clouds using a suite of ice nucleation measurement techniques – an expansion cloud chamber, a continuous-flow diffusion chamber, and a cold stage. In order to compare the measurements made using the different instruments, we have normalized the data in relation to the mass of salt present in the nascent sea spray aerosol. At temperatures above 248 K some of the SML samples were very effective at nucleating ice, but there was substantial variability between the different samples. In contrast, there was much less variability between samples below 248 K. We discuss our results in the context of aerosol–cloud interactions in the Arctic with a focus on furthering our understanding of which INP types may be important in the Arctic atmosphere.

scholarly journals Ice nucleating particles in Canadian Arctic sea–surface microlayer and bulk seawater

2017 ◽  
Author(s):  
Victoria E. Irish ◽  
Pablo Elizondo ◽  
Jessie Chen ◽  
Cédric Chou ◽  
Joannie Charette ◽  
...  
Keyword(s):  
North America ◽  
Canadian Arctic ◽  
Sea Surface ◽  
The Arctic ◽  
Surface Microlayer ◽  
Strong Negative Correlation ◽  
Spatial And Temporal Distributions ◽  
Sea Surface Microlayer ◽  
Freezing Temperatures ◽  
Seawater Samples

Abstract. The sea–surface microlayer and bulk seawater can contain ice-nucleating particles (INPs) and these INPs can be emitted into the atmosphere. Our current understanding of the properties, concentrations, spatial and temporal distributions of INPs in the microlayer and bulk seawater is limited. In this study we investigate the concentrations and properties of INPs in microlayer and bulk seawater samples collected in the Canadian Arctic during the summer of 2014. INPs were ubiquitous in the microlayer and bulk seawater with freezing temperatures as high as −14 °C. A strong negative correlation (R = −0.7, p = 0.02) was observed between salinity and freezing temperatures (after correction for freezing depression by the salts). One possible explanation is that INPs were associated with melting sea ice. Heat and filtration treatments of the samples show that the INPs were likely biological materials with sizes between 0.02 μm and 0.2 μm in diameter, consistent with previous measurements off the coast of North America and near Greenland in the Arctic. The concentrations of INPs in the microlayer and bulk seawater were consistent with previous measurements at several other locations off the coast of North America. However, our average microlayer concentration was lower than previous observations made near Greenland in the Arctic. This difference could not be explained by chlorophyll a concentrations derived from satellite measurements. In addition, previous studies found significant INP enrichment in the microlayer, relative to bulk seawater, which we did not observe in this study. While further studies are needed to understand these differences, we confirm that there is a source of INP in the microlayer and bulk seawater in the Canadian Arctic that may be important for atmospheric INP concentrations.

scholarly journals Ice-nucleating particles in Canadian Arctic sea-surface microlayer and bulk seawater

2017 ◽  
Vol 17 (17) ◽  
pp. 10583-10595 ◽  
Author(s):  
Victoria E. Irish ◽  
Pablo Elizondo ◽  
Jessie Chen ◽  
Cédric Chou ◽  
Joannie Charette ◽  
...  
Keyword(s):  
North America ◽  
Canadian Arctic ◽  
Sea Surface ◽  
The Arctic ◽  
Surface Microlayer ◽  
Strong Negative Correlation ◽  
Spatial And Temporal Distributions ◽  
Sea Surface Microlayer ◽  
Freezing Temperatures ◽  
Seawater Samples

Abstract. The sea-surface microlayer and bulk seawater can contain ice-nucleating particles (INPs) and these INPs can be emitted into the atmosphere. Our current understanding of the properties, concentrations, and spatial and temporal distributions of INPs in the microlayer and bulk seawater is limited. In this study we investigate the concentrations and properties of INPs in microlayer and bulk seawater samples collected in the Canadian Arctic during the summer of 2014. INPs were ubiquitous in the microlayer and bulk seawater with freezing temperatures in the immersion mode as high as −14 °C. A strong negative correlation (R = −0. 7, p = 0. 02) was observed between salinity and freezing temperatures (after correction for freezing depression by the salts). One possible explanation is that INPs were associated with melting sea ice. Heat and filtration treatments of the samples show that the INPs were likely heat-labile biological materials with sizes between 0.02 and 0.2 µm in diameter, consistent with previous measurements off the coast of North America and near Greenland in the Arctic. The concentrations of INPs in the microlayer and bulk seawater were consistent with previous measurements at several other locations off the coast of North America. However, our average microlayer concentration was lower than previous observations made near Greenland in the Arctic. This difference could not be explained by chlorophyll a concentrations derived from satellite measurements. In addition, previous studies found significant INP enrichment in the microlayer, relative to bulk seawater, which we did not observe in this study. While further studies are needed to understand these differences, we confirm that there is a source of INP in the microlayer and bulk seawater in the Canadian Arctic that may be important for atmospheric INP concentrations.

scholarly journals Microlayer source of oxygenated volatile organic compounds in the summertime marine Arctic boundary layer

2017 ◽  
Vol 114 (24) ◽  
pp. 6203-6208 ◽  
Author(s):  
Emma L. Mungall ◽  
Jonathan P. D. Abbatt ◽  
Jeremy J. B. Wentzell ◽  
Alex K. Y. Lee ◽  
Jennie L. Thomas ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Volatile Organic Compounds ◽  
Organic Compounds ◽  
Sea Surface ◽  
The Arctic ◽  
Surface Microlayer ◽  
Marine Environments ◽  
Sea Surface Microlayer ◽  
Oxygenated Volatile Organic Compounds ◽  
Volatile Organic

Summertime Arctic shipboard observations of oxygenated volatile organic compounds (OVOCs) such as organic acids, key precursors of climatically active secondary organic aerosol (SOA), are consistent with a novel source of OVOCs to the marine boundary layer via chemistry at the sea surface microlayer. Although this source has been studied in a laboratory setting, organic acid emissions from the sea surface microlayer have not previously been observed in ambient marine environments. Correlations between measurements of OVOCs, including high levels of formic acid, in the atmosphere (measured by an online high-resolution time-of-flight mass spectrometer) and dissolved organic matter in the ocean point to a marine source for the measured OVOCs. That this source is photomediated is indicated by correlations between the diurnal cycles of the OVOC measurements and solar radiation. In contrast, the OVOCs do not correlate with levels of isoprene, monoterpenes, or dimethyl sulfide. Results from box model calculations are consistent with heterogeneous chemistry as the source of the measured OVOCs. As sea ice retreats and dissolved organic carbon inputs to the Arctic increase, the impact of this source on the summer Arctic atmosphere is likely to increase. Globally, this source should be assessed in other marine environments to quantify its impact on OVOC and SOA burdens in the atmosphere, and ultimately on climate.

scholarly journals n-Alkanes, PAHs and surfactants in the sea surface microlayer and sea water samples of the Gerlache Inlet sea (Antarctica)

2009 ◽  
Vol 92 (1) ◽  
pp. 37-43 ◽  
Author(s):  
A.M. Stortini ◽  
T. Martellini ◽  
M. Del Bubba ◽  
L. Lepri ◽  
G. Capodaglio ◽  
...  
Keyword(s):  
Water Samples ◽  
Sea Water ◽  
Sea Surface ◽  
Surface Microlayer ◽  
Sea Surface Microlayer

scholarly journals Terrestrial or marine – indications towards the origin of ice-nucleating particles during melt season in the European Arctic up to 83.7° N

2021 ◽  
Vol 21 (15) ◽  
pp. 11613-11636
Author(s):  
Markus Hartmann ◽  
Xianda Gong ◽  
Simonas Kecorius ◽  
Manuela van Pinxteren ◽  
Teresa Vogl ◽  
...  
Keyword(s):  
Diffusion Chamber ◽  
Ice Nucleation ◽  
Biologically Active ◽  
The Arctic ◽  
Surface Microlayer ◽  
Fog Water ◽  
Sea Surface Microlayer ◽  
European Arctic ◽  
Almost All

Abstract. Ice-nucleating particles (INPs) initiate the primary ice formation in clouds at temperatures above ca. −38 ∘C and have an impact on precipitation formation, cloud optical properties, and cloud persistence. Despite their roles in both weather and climate, INPs are not well characterized, especially in remote regions such as the Arctic. We present results from a ship-based campaign to the European Arctic during May to July 2017. We deployed a filter sampler and a continuous-flow diffusion chamber for offline and online INP analyses, respectively. We also investigated the ice nucleation properties of samples from different environmental compartments, i.e., the sea surface microlayer (SML), the bulk seawater (BSW), and fog water. Concentrations of INPs (NINP) in the air vary between 2 to 3 orders of magnitudes at any particular temperature and are, except for the temperatures above −10 ∘C and below −32 ∘C, lower than in midlatitudes. In these temperature ranges, INP concentrations are the same or even higher than in the midlatitudes. By heating of the filter samples to 95 ∘C for 1 h, we found a significant reduction in ice nucleation activity, i.e., indications that the INPs active at warmer temperatures are biogenic. At colder temperatures the INP population was likely dominated by mineral dust. The SML was found to be enriched in INPs compared to the BSW in almost all samples. The enrichment factor (EF) varied mostly between 1 and 10, but EFs as high as 94.97 were also observed. Filtration of the seawater samples with 0.2 µm syringe filters led to a significant reduction in ice activity, indicating the INPs are larger and/or are associated with particles larger than 0.2 µm. A closure study showed that aerosolization of SML and/or seawater alone cannot explain the observed airborne NINP unless significant enrichment of INP by a factor of 105 takes place during the transfer from the ocean surface to the atmosphere. In the fog water samples with −3.47 ∘C, we observed the highest freezing onset of any sample. A closure study connecting NINP in fog water and the ambient NINP derived from the filter samples shows good agreement of the concentrations in both compartments, which indicates that INPs in the air are likely all activated into fog droplets during fog events. In a case study, we considered a situation during which the ship was located in the marginal sea ice zone and NINP levels in air and the SML were highest in the temperature range above −10 ∘C. Chlorophyll a measurements by satellite remote sensing point towards the waters in the investigated region being biologically active. Similar slopes in the temperature spectra suggested a connection between the INP populations in the SML and the air. Air mass history had no influence on the observed airborne INP population. Therefore, we conclude that during the case study collected airborne INPs originated from a local biogenic probably marine source.

scholarly journals Terrestrial or marine? – Indications towards the origin of Ice Nucleating Particles during melt season in the European Arctic up to 83.7° N

2020 ◽  
Author(s):  
Markus Hartmann ◽  
Xianda Gong ◽  
Simonas Kecorius ◽  
Manuela van Pinxteren ◽  
Teresa Vogl ◽  
...  
Keyword(s):  
Diffusion Chamber ◽  
Ice Nucleation ◽  
Biologically Active ◽  
The Arctic ◽  
Surface Microlayer ◽  
Fog Water ◽  
Sea Surface Microlayer ◽  
European Arctic ◽  
Almost All

Abstract. Ice nucleating particles (INPs) initiate the primary ice formation in clouds at temperatures above ca. −38° C and have an impact on precipitation formation, cloud optical properties and cloud persistence. Despite their roles in both weather and climate, INPs are not well characterized, especially in remote regions such as the Arctic. We present results from a ship-based campaign to the European Arctic in May to July 2017. We deployed a filter sampler and a continuous flow diffusion chamber for off- and online INP analysis, respectively. We also investigated the ice nucleation properties of samples from different environmental compartments, i.e., the sea surface microlayer (SML), the bulk seawater (BSW), and fog water. Concentrations of INP (NINP) in the air vary between two to three orders of magnitudes at any particular temperature and are, except for the temperatures above −10° C and below −32° C, lower than in mid-latitudes. In these temperature ranges INP concentrations are the same or even higher than in the mid-latitudes. Heating of the filter samples to 95° C for 1 hour we found a significant reduction in ice nucleation activity, i.e., indications that the INPs active at warmer temperatures are biogenic. At colder temperatures the INP population was likely dominated by mineral dust. The SML was found to be enriched in INP compared to the BSW in almost all samples. The enrichment factor (EF) varied mostly between 1 and 10, but EFs as high as 94.97 were also observed. Filtration of the seawater samples with 0.2 µm syringe filters lead to a significant reduction in ice activity, indicating the INPs are larger, and/or are associated with particles larger than 0.2 µm. A closure study showed that aerosolization of SML and/or seawater alone cannot explain the observed air-borne NINP unless significant enrichment of INP by a factor of 105 takes place during the transfer from the ocean surface to the atmosphere. In the fog water samples with −3.47° C we observed the highest freezing onset of any sample. A closure study connecting NINP in fog water and the ambient NINP derived from the filter samples shows good agreement of the concentrations in both compartments, which indicates that INPs in the air are likely all activated into fog droplets during fog events. In a case study we considered a situation during which the ship was located in the marginal sea ice zone and NINP in air and the SML were highest in the temperature range above −10° C. Chlorophyll-a measurements by satellite remote sensing point towards the waters in the investigated region being biologically active. Heat induced reduction of ice nucleating ability indicated the biogenic nature of the air-borne INPs. Similar slopes in the temperature spectra suggested a connection between the INP populations in the SML and the air. Air mass history had no influence on the observed air-borne INP population. Therefore, we conclude that during the case study collected air-borne INPs originated from a local biogenic probably marine source.

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