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

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.

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

10.5194/acp-2020-1211 ◽

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

Environmental Science & Technology ◽

10.1021/acs.est.7b04072 ◽

2018 ◽

Vol 52 (4) ◽

pp. 1817-1826 ◽

Cited By ~ 9

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

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

Atmospheric Chemistry and Physics ◽

10.5194/acp-20-11089-2020 ◽

2020 ◽

Vol 20 (18) ◽

pp. 11089-11117 ◽

Cited By ~ 3

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.

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

10.5194/egusphere-egu21-9789 ◽

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

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.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&#176;N, between 0&#176; and 35&#176;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.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&#176;C and below -30&#176;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: a) all INP in the air are activated to fog droplets, and b) the INP concentration in seawater alone cannot explain INP concentration in air without a substantial enrichment of INP (factor 104 to 105) during the transfer of INP from the sea surface to the atmosphere.&#160; 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&#176;C. These findings highlight the need for future studies to assess especially the production mechanisms and source strength for Arctic INP.We gratefully acknowledge the funding by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) &#8211; Projektnummer 268020496 &#8211; TRR 172, within the Transregional Collaborative Research Center &#8220;ArctiC Amplification: Climate Relevant Atmospheric and SurfaCe Processes, and Feedback Mechanisms (AC)3

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New insights into aerosol and climate in the Arctic

10.5194/acp-2018-995 ◽

2018 ◽

Cited By ~ 2

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.

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

Atmospheric Chemistry and Physics ◽

10.5194/acp-19-2527-2019 ◽

2019 ◽

Vol 19 (4) ◽

pp. 2527-2560 ◽

Cited By ~ 40

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).

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The organic sea-surface microlayer in the upwelling region off the coast of Peru and potential implications for air–sea exchange processes

Biogeosciences ◽

10.5194/bg-13-989-2016 ◽

2016 ◽

Vol 13 (4) ◽

pp. 989-1007 ◽

Cited By ~ 47

Author(s):

Anja Engel ◽

Luisa Galgani

Keyword(s):

Amino Acids ◽

Organic Matter ◽

Wind Speed ◽

Coastal Upwelling ◽

Sea Surface ◽

Surface Microlayer ◽

Close Coupling ◽

Exchange Processes ◽

Sea Surface Microlayer ◽

Almost All

Abstract. The sea-surface microlayer (SML) is at the uppermost surface of the ocean, linking the hydrosphere with the atmosphere. The presence and enrichment of organic compounds in the SML have been suggested to influence air–sea gas exchange processes as well as the emission of primary organic aerosols. Here, we report on organic matter components collected from an approximately 50 µm thick SML and from the underlying water (ULW), ∼  20 cm below the SML, in December 2012 during the SOPRAN METEOR 91 cruise to the highly productive, coastal upwelling regime off the coast of Peru. Samples were collected at 37 stations including coastal upwelling sites and off-shore stations with less organic matter and were analyzed for total and dissolved high molecular weight (> 1 kDa) combined carbohydrates (TCCHO, DCCHO), free amino acids (FAA), total and dissolved hydrolyzable amino acids (THAA, DHAA), transparent exopolymer particles (TEP), Coomassie stainable particles (CSPs), total and dissolved organic carbon (TOC, DOC), total and dissolved nitrogen (TN, TDN), as well as bacterial and phytoplankton abundance. Our results showed a close coupling between organic matter concentrations in the water column and in the SML for almost all components except for FAA and DHAA that showed highest enrichment in the SML on average. Accumulation of gel particles (i.e., TEP and CSP) in the SML differed spatially. While CSP abundance in the SML was not related to wind speed, TEP abundance decreased with wind speed, leading to a depletion of TEP in the SML at about 5 m s−1. Our study provides insight to the physical and biological control of organic matter enrichment in the SML, and discusses the potential role of organic matter in the SML for air–sea exchange processes.

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

10.5194/acp-2017-384 ◽

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.

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Influence of springtime atmospheric circulation types on the distribution of air pollutants in the Arctic

10.5194/acp-2021-458 ◽

2021 ◽

Author(s):

Manu Anna Thomas ◽

Abhay Devasthale ◽

Tiina Nygård

Keyword(s):

Atmospheric Circulation ◽

The Arctic ◽

Transport Models ◽

Self Organizing Maps ◽

Atmospheric Circulation Patterns ◽

Circulation Types ◽

Circulation Patterns ◽

European Arctic ◽

Pollutant Distribution ◽

Almost All

Abstract. The transport and distribution of short-lived climate forcers in the Arctic is influenced by the prevailing atmospheric circulation patterns. Understanding the coupling between pollutant distribution and dominant atmospheric circulation types is therefore important, not least to understand the processes governing the local processing of pollutants in the Arctic, but also to test the fidelity of chemistry transport models to simulate the transport from the southerly latitudes. Here, we use a combination of satellite based and reanalysis datasets spanning over 12 years (2007–2018) and investigate the concentrations of NO2, O3, CO and aerosols and their co-variability during 20 different atmospheric circulation types in the spring season (March, April and May) over the Arctic. We carried out a Self-Organizing Maps analysis of MSLP to derive these circulation types. Although almost all pollutants investigated here show statistically significant sensitivity to the circulation types, NO2 exhibits the strongest sensitivity among them. The circulation types with low-pressure systems located over the northeast Atlantic show a clear enhancement of NO2 and AOD in the European Arctic. The O3 concentrations are, however, decreased. The free tropospheric CO is increased over the Arctic during such events. The circulation types with atmospheric blocking over Greenland and northern Scandinavia show the opposite signal in which the NO2 concentrations are decreased and AODs are smaller than the climatological values. The O3 concentrations are, however, increased and the free tropospheric CO decreased during such events. The study provides the most comprehensive assessment so far of the sensitivity of springtime pollutant distribution to the atmospheric circulation types in the Arctic and also provides an observational basis for the evaluation of chemistry transport models.

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Heterogeneous ice nucleation ability of aerosol particles generated from Arctic sea surface microlayer and surface seawater samples at cirrus temperatures

Atmospheric Chemistry and Physics ◽

10.5194/acp-21-13903-2021 ◽

2021 ◽

Vol 21 (18) ◽

pp. 13903-13930

Author(s):

Robert Wagner ◽

Luisa Ickes ◽

Allan K. Bertram ◽

Nora Els ◽

Elena Gorokhova ◽

...

Keyword(s):

Aerosol Particles ◽

Ice Nucleation ◽

Sea Surface ◽

Ice Formation ◽

Sea Spray ◽

Surface Microlayer ◽

Sea Surface Microlayer ◽

Sea Spray Aerosol ◽

Seawater Samples ◽

Heterogeneous Ice Nucleation

Abstract. Sea spray aerosol particles are a recognised type of ice-nucleating particles under mixed-phase cloud conditions. Entities that are responsible for the heterogeneous ice nucleation ability include intact or fragmented cells of marine microorganisms as well as organic matter released by cell exudation. Only a small fraction of sea spray aerosol is transported to the upper troposphere, but there are indications from mass-spectrometric analyses of the residuals of sublimated cirrus particles that sea salt could also contribute to heterogeneous ice nucleation under cirrus conditions. Experimental studies on the heterogeneous ice nucleation ability of sea spray aerosol particles and their proxies at temperatures below 235 K are still scarce. In our article, we summarise previous measurements and present a new set of ice nucleation experiments at cirrus temperatures with particles generated from sea surface microlayer and surface seawater samples collected in three different regions of the Arctic and from a laboratory-grown diatom culture (Skeletonema marinoi). The particles were suspended in the Aerosol Interaction and Dynamics in the Atmosphere (AIDA) cloud chamber and ice formation was induced by expansion cooling. We confirmed that under cirrus conditions, apart from the ice-nucleating entities mentioned above, also crystalline inorganic salt constituents can contribute to heterogeneous ice formation. This takes place at temperatures below 220 K, where we observed in all experiments a strong immersion freezing mode due to the only partially deliquesced inorganic salts. The inferred ice nucleation active surface site densities for this nucleation mode reached a maximum of about 5×1010 m−2 at an ice saturation ratio of 1.3. Much smaller densities in the range of 108–109 m−2 were observed at temperatures between 220 and 235 K, where the inorganic salts fully deliquesced and only the organic matter and/or algal cells and cell debris could contribute to heterogeneous ice formation. These values are 2 orders of magnitude smaller than those previously reported for particles generated from microlayer suspensions collected in temperate and subtropical zones. While this difference might simply underline the strong variability of the number of ice-nucleating entities in the sea surface microlayer across different geographical regions, we also discuss how instrumental parameters like the aerosolisation method and the ice nucleation measurement technique might affect the comparability of the results amongst different studies.

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