This session, inspired by the goals of initiatives such as QuiESCENT (Quantifying the Indirect Effect: from Sources to Climate Effects of Natural and Transported aerosol in the Arctic), CATCH (Cryosphere and ATmospheric CHemistry), CIce2Clouds (Coupling of ocean-ice-atmosphere processes: from sea-Ice biogeochemistry to aerosols and Clouds), and BEPSII (Biogeochemical exchanges at Sea Ice Interfaces), aims to foster interdisciplinary collaboration by bringing together researchers studying aerosols, clouds, ocean–ice biogeochemistry, and their coupled interactions in both the Arctic and Antarctic. We seek to bridge disciplinary gaps—spanning aerosols and clouds, physics and chemistry, observations and modeling, and ocean–ice–atmosphere processes—to advance our understanding of polar climate systems.
We invite contributions that address the following key topics:
- Aerosol-cloud interactions: Their influence on cloud microphysics, radiative properties, and precipitation patterns in polar environments, including the contrasting effects of anthropogenic pollution and natural aerosols.
- Biogeochemical cycling: Marine and terrestrial sources of aerosols, including sea salt, mineral dust, biological particles, black carbon, and organic aerosols, and their feedbacks with atmospheric components.
- Boundary layer dynamics: The role of atmospheric and oceanic boundary layer processes in shaping aerosol and cloud properties, as well as their impact on boundary layer mixing and local pollution processing.
- Observational and modeling advances: Innovations in field campaigns, remote sensing, laboratory experiments, and modeling frameworks to improve the representation of polar aerosol–cloud–ocean–ice systems in climate models.
- Climate feedbacks and projections: Implications of polar aerosol–cloud interactions for climate model performance and global climate predictions, with a focus on reducing uncertainties in projections.
Orals: Mon, 4 May, 16:15–18:00 | Room M2
The NASA Arctic Radiation-Cloud-Aerosol-Surface-Interaction Experiment (ARCSIX) was an extensive aircraft mission in the Spring and Summer of 2024 that was designed to characterize the connections between radiation, the atmosphere, and the cryosphere over the course of a melt season in the Arctic Ocean North of Greenland and Canada. It tracked the evolution of multi-year and seasonal sea ice in response to varying cloud, aerosol and surface conditions while simultaneously probing the life cycle of clouds – especially for thin low-level mixed-phase boundary layer systems, which were encountered frequently and often persisted for multiple days. These clouds likely contribute to the Spring surface melt to a greater extent than previously known, and yet they are often difficult to even detect with satellite imagers in low Earth orbit.
Up to three aircraft with a payload comprising remote sensing, radiation, cloud and aerosol microphysics and composition, and thermodynamic measurements, were strategically collocated to observe different aspects of co-evolving cloud-aerosol systems in the vertical, horizontal, and temporal dimension. In some cases, airmasses were tracked over 2-3 days. ARCSIX reached deep into the Arctic and provides a wealth of statistics on interconnected cloud, aerosol, and surface properties. It captured a broad range of surface and thermodynamic states and even tracked an anomalous sea ice melt event – a harbinger of what is to come in a seasonally ice-free Arctic.
We will provide an overview of the mission and present first results, some of which are challenging the current understanding of a region that is undergoing the most rapid climate-driven changes of the globe. Drawing on ARCSIX data, we will convey some new ideas about the maintenance of mysteriously long-lived warm boundary layer Arctic clouds, with the goal of engaging a broader community in the analysis of the ARCSIX data set.
How to cite: Schmidt, S., Taylor, P., and Boisvert, L.: NASA’s Arctic Radiation-Cloud-Aerosol-Surface-Interaction Experiment (ARCSIX) – Mission Overview and First Results, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-16271, https://doi.org/10.5194/egusphere-egu26-16271, 2026.
During the ARTofMELT 2023 expedition (8 May–14 June) aboard the icebreaker Oden, we investigated the High Arctic aerosol system across the transition from late spring into sea-ice melt onset. Submicron aerosol properties were characterized using high-resolution soot particle aerosol mass spectrometry (SP-AMS; chemical composition, organic fingerprints and elemental ratios), complemented by measurements of equivalent black carbon (eBC), particle size distributions, back-trajectory analysis, and size-segregated offline analyses by means of ion chromatography and total carbon analysis. We identified nine regimes, spanning Arctic-confined conditions, warm-air intrusions, and fog sampling.
Campaign-average submicron particulate matter (PM1) was sulfate-dominated (66% sulfate, 29% organic aerosol OA, minor nitrate, ammonium and chloride; eBC ~1%), but approaching the melt onset variability shifted from accumulation-mode, sulfate-rich background conditions to Aitken-mode dominated aerosols with higher relative contribution from OA. The analysis of the OA fragmentation patterns showed a persistently oxidized background, repeatedly perturbed by transport and fog, with coherent shifts toward fresher material (lower f44 and O:C, higher H:C) coinciding with Aitken-mode dominance. Size-resolved total carbon (TC) measurements (<4 µm) indicate that TC was concentrated at diameters below ~0.15 µm, and its loading increased in air masses that travelled over open water. Toward melt onset, we observed increases in methanesulfonic acid (MSA) concentration and non-sea-salt sulfate, consistent with a stronger relative contribution from marine/organosulfur compounds. Overall, the depletion of accumulation mode particles during the early melt season favors CCN-relevant Aitken-mode carbon in the High Arctic.
How to cite: Fellin, D., Heikkinen, L., Mattsson, F., Kojoj, J., Haberstock, L., Zang, C., Thomsen, L., Mohr, C., Riipinen, I., Ickes, L., Willis, M., Glasius, M., Barbaro, E., Gambaro, A., Zieger, P., and Gilardoni, S.: Aerosol composition shifts in the High Arctic during the sea ice melt onset (ARTofMELT2023), EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18722, https://doi.org/10.5194/egusphere-egu26-18722, 2026.
Global climate models perform particularly poorly over the Southern Ocean, resulting in persistent cloud and radiation biases. This is in part driven by incomplete understanding of the aerosol formation and transformations over the Southern Ocean and their influence cloud formation and properties. Oxidation of volatile sulfur compounds, in particular dimethyl sulfide (DMS), and the subsequent secondary particle formation, is an important source of aerosols in the Southern Ocean atmosphere (and in marine environments in general). This presentation will focus on terminal oxidation products of volatile sulfur compounds, namely sulfuric acid (SA) and methanesulfonic acid (MSA), in both gas and particle phase observed during the 2024 Multidisciplinary Investigations of the Southern Ocean (MISO) voyage (Jan – March 2024) aboard the Australian Research Vessel Investigator and covering the western Pacific sector of the Southern Ocean (110o – 150o E). These species are investigated and will be presented in the context of air mass origin and synoptic meteorology.
A notable feature of the voyage were periods of elevated gaseous MSA south of ~62o S, coinciding with increased particulate sulfate and MSA, as well as enhanced cloud condensation nuclei (CCN) concentrations. These periods were found to be associated with Antarctic continental outflow and the air masses to have free tropospheric origin. By using E-AIM thermodynamic modelling we show that aerosol particles during MISO voyage were highly acidic (pH < -1) and that the elevated gaseous MSA is a result of evaporation from these highly acidic particles. Evaporation of MSA from highly acidic aerosols during Antarctic continental outflow has already been reported for the 2018 CAPRICORN-2 voyage which covered a very similar geographical region (Miljevic et al., 2025). The recent MISO voyage further highlights long range transport as an important pathway for biogenically dominated CCN and brings into focus MSA gas-particle partitioning as a relevant process in the marine sulfur cycle.
Reference:
Miljevic, B., Mallet, M. D., Osuagwu, C. G., Ristovski, Z. D., Humphries, R. S., Selleck, P., Taylor, S., & Keywood, M. D. (2025). Aerosol acidity controls methanesulfonic acid evaporation from aerosols during Antarctic katabatic outflow. Communications Earth & Environment, 6(1), 1057. https://doi.org/10.1038/s43247-025-03041-2
How to cite: Miljevic, B., Alroe, J., Mallet, M. D., Muniraj Saraswathy, A., Protat, A., Mace, G. G., Barber, K., Avaronthan Veettil, S., Alinejadtabrizi, T., Humphries, R. S., and Taylor, S.: Antarctic Continental Outflow as a Transport Pathway for Elevated Gaseous MSA and Biogenically Dominated Cloud Condensation Nuclei: Insights from the MISO Voyage, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6049, https://doi.org/10.5194/egusphere-egu26-6049, 2026.
Understanding the complex interactions between aerosols, cloud microphysics, and dynamics is essential for accurately predicting cloud behavior and its impacts on the climate system. One of the key open questions concerns how cloud liquid water path responds to changes in cloud droplet number concentration. Turbulent mixing, initiated by radiative cooling near the cloud top, plays a central role in this feedback by modifying cloud microphysical properties. This mechanism has been suggested as a primary explanation for the observed reduction in cloud liquid water content with increasing aerosol concentration over the global oceans.
In this study, we provide new insights based on observations of subarctic low-level clouds combined with model-assisted analysis of the coupling between boundary-layer dynamics and cloud microphysical processes. The work benefits from unique measurement capabilities at Pallas, Finland, where unmanned aerial vehicle (UAV) systems can be operated up to 2000 m agl and beyond the visual line of sight, supported by ACTRIS cloud and aerosol measurement facilities. We present high-frequency surface-based and airborne in situ datasets collected using multiple cloud droplet sensors and compare them with surface-based remote sensing products. In addition, we employ UCLALES-SALSA, a large-eddy simulation model with sectional aerosol–cloud–precipitation microphysics, to investigate the processes controlling both mean cloud properties and the spatial variability of cloud droplet size distributions in relation to cloud dynamics. This combined observational and modeling approach improves our understanding of differences between surface-based and airborne in situ observations and provides high-quality reference data for the validation of remote sensing products.
How to cite: Romakkaniemi, S., Leskinen, A., Calderon, S., Hyttinen, N., Isopahkala, U., Doulgeris, K., Kaikkonen, V., Molkoselkä, E., Mäkynen, A., Moisseev, D., Komppula, M., and Brus, D.: Insights into Cloud Processes from In Situ UAV-Based Cloud Observations and Aerosol-Aware Numerical Simulations, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10880, https://doi.org/10.5194/egusphere-egu26-10880, 2026.
Greenlandic fjord ecosystems undergo accelerated change as they are at the nexus of the pressures from the ocean, ice, land and atmosphere. The Swiss Polar Institute Flagship program GreenFjord (Greenlandic fjord ecosystems in a changing climate: socio-cultural and environmental interactions) investigated biogeochemical aerosol processes in two contrasting fjords in southern Greenland between 2022 and 2025. One fjord represented a system, where glaciers still terminate in the ocean (marine-terminating fjord), while another represented a system, where only streams from land-terminating glaciers (land-terming fjord) enter the ocean. The two ways of adding fresh-water result in very different fjord dynamics of water and nutrient movement, and therefore in different microbial productivity. In addition, the land surface types surrounding the fjords are also distinct.
From an ocean perspective and to understand if these differences impact atmospheric chemical composition, we performed measurements of new particle formation, volatile organic compounds and aerosol chemical composition, and find indeed different processes across the fjords with impacts on the cloud condensation nuclei (CCN) budget. From a land perspective, in a land-terminating system, glacial outwash plains typically form and constitute potentially large sources of ice nucleating particles (INP). We investigated the freezing spectra and atmospheric contribution of glacial dust to the aerosol population.
This presentation will provide an overview of the GreenFjord project and delves into the natural contribution of CCN and INP from fjord systems.
How to cite: Schmale, J., Alden, J., Bergner, N., and Surdu, M. and the GreenFjord Project Team: Biogeochemical aerosol processes in Southern Greenlandic fjord systems, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6826, https://doi.org/10.5194/egusphere-egu26-6826, 2026.
There is a strong need to determine how boundary cloud properties vary with surface, environmental and aerosol conditions in high latitudes during cold air outbreaks (CAOs) to determine processes controlling the evolution of these clouds. In-situ cloud microphysical, thermodynamic, and remote sensing measurements made on a C130 aircraft during the 2024 CAO Experiment in the Sub-Arctic Region (CAESAR) field campaign over the Norwegian and Greenland Sea are used to quantify how vertical cloud and thermodynamic profiles vary with environmental conditions, and how they transform downstream from the ice edge to warmer oceans. The majority of clouds sampled were either liquid- or mixed-phase, with few entirely ice-phase clouds. Ramped ascents and descents through cloud are used to determine how vertical profiles of total number concentration, liquid water content, ice crystal concentration, ice mass content, liquid and ice effective radius, and median volume diameter as functions of normalized altitude (zn, where zn=0 at cloud base and zn=1 at cloud top) vary with environmental conditions. Results show considerable variability, but profiles exhibit clear dependence on estimated inversion strength (EIS), with higher cloud droplet number concentrations, lower effective radii for liquid and ice particles, and lower large ice crystal number concentration and water content for higher EIS. Dependence on other environmental conditions will also be shown. Data from the 16 March 2024 flight when 36 dropsondes were released, are then used to determine how cloud and environmental properties vary across five distinct zones: the sea ice zone, zone near the edge of the sea ice with shallow cumulus clouds, zone characterized by well-organized cloud streets, zone featuring disorganized cloud streets on northern side of a polar low, and the polar low zone. Environmental parameters, including the M index, LTS (lower tropospheric stability), EIS, boundary layer (BL) height, and the vertical distribution of temperature and humidity within the BL, vary across these five zones. Additionally, cloud macrophysical properties such as cloud top and base heights and temperature, cloud cell width, number within a 50-km observation window, and cloud albedo, along with microphysical properties including liquid water content and liquid water fraction (LWF), also change across zones. These variations highlight the spatial, macro- and micro-physical, and thermodynamic gradients as CAO air moves downstream. To uncover mechanisms driving differences in zone properties, simulations conducted with the Weather Research and Forecasting (WRF) model shown to reproduce observed cloud patterns and vertical structures, are utilized. WRF simulations reveal that mixed-phase shallow cumulus located near the sea ice edge contained a supercooled liquid layer near their tops. These clouds had higher LWF near cloud top compared to both well-organized and disorganized cloud streets. Additionally, polar low clouds primarily consisted of ice. A Random Forest model, utilizing WRF output, shows LTS was the most important factor in predicting the number of cloud cells. In contrast, relative humidity (RH) between 0 and 2 km had the greatest influence on cloud cell width and cloud base height, while RH between 2 and 4 km was most critical for predicting cloud base heights.
How to cite: McFarquhar, G., Xia, Z., Huang, Y., Amundsen, N., Geerts, B., Vomel, H., Wang, Z., and Zuidema, P.: What Controls the Macrophysical and Microphysical Properties of Arctic Clouds during Cold Air Outbreaks: Results from CAESAR, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8139, https://doi.org/10.5194/egusphere-egu26-8139, 2026.
Anthropogenic aerosols can have a significant impact on the Earth’s radiation budget through their interactions with clouds. The effective radiative forcing due to aerosol-cloud interactions (ERFaci) is believed to be negative globally, albeit with significant uncertainty. Despite the region experiencing rapid climate change, climate models have so far failed to constrain the sign of ERFaci in the Arctic, while observation-based estimates of ERFaci in the polar regions are challenging due to a relative lack of ground-based observatories and uncertainties in satellite retrievals.
Here we provide an observation-based estimate of the top-of-atmosphere radiative forcing due to aerosol-cloud interactions in the Arctic using passive remote sensing satellite data and aerosol reanalyses. To address potential satellite retrieval errors over sea ice and at high latitudes, we use observed cloud optical thickness from the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) to measure the accuracy of passive retrievals of cloud properties from the Moderate Resolution Imaging Spectrometer (MODIS). We find strong agreement on cloud detection for optically thicker clouds, which represent the large majority of the clouds used in this study.
The effective radiative forcing from adjustments in cloud fraction and cloud water path are calculated using droplet number concentration as a mediating variable. The ERFaci in liquid clouds over the Arctic ocean and sea ice is found to be negative on average, with a stronger forcing over the ocean. Negative forcings from instantaneous changes in cloud droplet number concentration and subsequent cloud fraction adjustments are partially offset by a positive forcing caused by apparent decreases in cloud water path. The data suggests that the overall ERFaci in the Arctic is more likely negative compared to previous estimates from model outputs, but smaller in magnitude compared to lower latitudes due to reduced insolation and higher surface albedo. As anthropogenic aerosol emissions in the Arctic are expected to increase in the coming decades, a stronger ERFaci could follow and partially offset other positive forcings. These results for the present-day forcing could constrain model outputs of future Arctic radiative forcing, reducing the contribution of aerosol-cloud processes to the overall uncertainty.
How to cite: O'Flanagan, O. and Gryspeerdt, E.: Observational constraints on Arctic radiative forcing due to aerosol-cloud interactions, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12350, https://doi.org/10.5194/egusphere-egu26-12350, 2026.
The Arctic is warming at unprecedented rates, yet climate models struggle to accurately represent key processes such as aerosol–cloud interactions in polar regions. The coexistence and interactions of liquid droplets and ice crystals within clouds, and the influence of aerosols acting as ice-nucleating particles or condensation nuclei, remain poorly understood because of the complexity of the microphysical processes involved. Previous studies have primarily focused on the relationship between cloud phase and instantaneous aerosol properties, often neglecting the physico-chemical evolution of air parcels during long-range transport.
To address this gap, we introduce the ARctic Clouds History and ThermodYnamic PhasE dataset (ARCHTYPE), which leverages DARDAR-MASKv2 retrieval products. These products combine data from the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) and the CloudSat Cloud Profiling Radar (CPR), both part of the A-Train constellation. In DARDAR-MASKv2, each atmospheric pixel (60 m vertical resolution, 1.7 km along-track) is classified into specific categories, for example, warm rain, clear sky, or ice cloud. Using a cloud detection algorithm, we extract cloud positions and parameters, including ice fraction and the spatial distribution of ice and liquid pockets within mixed-phase clouds.
For each identified cloud, we compute 96-hour back trajectories initialised at the top layer of the cloud using NOAA’s Hybrid Single-Particle Lagrangian Integrated Trajectory model (HYSPLIT) with the European Centre for Medium-Range Weather Forecasts Reanalysis v5 (ERA5) reanalysis as input meteorological data. We then co-locate along the back trajectories several environmental parameters: sea ice concentration from the Advanced Microwave Scanning Radiometer satellite observations (AMSR2), meteorological parameters from ERA5 and aerosol mixing ratios from the Modern-Era Retrospective analysis for Research and Applications, v2 (MERRA-2). The final ARCHTYPE product comprises millions of co-located back trajectories, offering a statistically robust dataset to investigate how air parcel history influences the thermodynamic phase of Arctic clouds.
In this presentation, we showcase the first results derived from this dataset, covering the period from 2006 to 2011. Preliminary analysis focusing on sea salt and dust aerosols indicates that cloud homogeneity increases with dust and decreases with sea salt. It also shows that, at low cloud top temperatures, ice fraction increases with dust content.
Beyond examining the general impact of air parcel history on cloud thermodynamic phases, we explore specific research questions: Are there regions that consistently receive aerosols from distant sources, and how do these transport patterns vary across the Arctic? What is the effect of sea ice variations on biogenic compound concentrations and sea spray aerosol production, and how does this influence low-level cloud formation? Finally, which aerosol ageing processes dominate during the long-range transport of air masses contributing to Arctic cloud formation?
How to cite: Castin, L., Coopman, Q., and Riedi, J.: Impact of air parcel history on Arctic cloud glaciation: a large-scale back trajectory analysis, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-3336, https://doi.org/10.5194/egusphere-egu26-3336, 2026.
Understanding ice nucleating particle (INP) concentrations, activation temperatures, and sources in the Arctic is necessary for constraining their contribution to Arctic amplification, due to their influence on the optical properties and lifetime of clouds. Despite this, Central Arctic INP observation studies are limited, and the relative contributions of local and long-range sources of INPs are not yet well understood. In this work, we present a dataset of year-round INP concentrations at 2-day resolution from aerosol filter samples taken during the 2019-20 MOSAiC (Multidisciplinary drifting Observatory for the Study of Arctic Climate) campaign, analysed using an immersion-mode droplet technique. We investigate the influence of long-range transportation events and local wind-blown sources on INP freezing spectra through comparisons with INPs measured from snow samples, major ions detected using ion chromatography, and aerosol concentrations in the diameter size range of 0.5–20 μm. We further constrain the impact of potential aerosol sources on total INP concentrations using a dilution series and background comparison method.
Our results show the presence of a distinct seasonal cycle, in agreement with previously reported observations. Warm-temperature INPs peak during summer, with INP concentrations at -15°C increasing to an average of 0.53 L-1 from 0.01 L-1 during the rest of the year. We also observe a period of low INP activity during November and December, ending with the onset of Arctic haze, and characterised by many samples being indistinguishable from background levels.
We observe a correlation between aerosol concentration and median INP activation temperature (R2 = 0.412). Our results show shifts to warmer activation temperatures on the order of 1 – 4 °C during aerosol peaks of more than 10 cm-3 above background associated with both blowing snow, and long-range transportation events. We use this to highlight the influence of total INP concentration on freezing spectra observed from droplet freezing experiments. To further constrain the impact of blowing snow events and long-range transportation on INP populations, we present a collection of case studies that have been analysed using a series of targeted dilutions and comparisons with background INP spectra.
How to cite: Malpas, M., Frey, M., van den Heuvel, F., and Yang, X.: Contributions of local and long-range sources to the annual cycle of Arctic ice nucleating particles, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-552, https://doi.org/10.5194/egusphere-egu26-552, 2026.
Aerosols serve as ice nucleating particles (INPs) and play a critical role in the formation of mixed-phase clouds. These clouds are prevalent in the lower and middle troposphere of the Arctic and exert a strong influence on both regional and global climate. However, limited understanding of INP sources and their temperature-dependent behavior has hindered accurate predictions ofaerosol-cloud interactions in the Arctic. In this study, we investigate the sources, spatial distributions, seasonal variations, and long-term changes of INPs in the Arctic using a global climate-aerosol model that explicitly represents INPs from three Arctic aerosol species: mineral dust, marine organic aerosols (MOA), and bioaerosols. Simulations covering the period 1981–2020 show that Arctic-sourced INPs account for more than 70% of total INPs in the Arctic lower troposphere. Dust is the largest contributor (36%), followed by bioaerosols (28%) and MOA (9%). They exhibit distinct spatial and seasonal patterns, underscoring the importance of representing multiple INP species and applying appropriate parameterizations for each when modeling INPs and mixed-phase clouds in the Arctic. Over the past four decades, Arctic warming increases local emissions of all three aerosol species by 4.7–18% because of the retreat of snow and sea ice. Nevertheless, INP concentrations in the Arctic lower troposphere decline by 19–29%, primarily because the INPs per unit aerosol mass decrease with increasing temperature. This indicates that the temperature-driven reduction of ice nucleating efficiency outweighs the emission-driven increase of INP abundance, except in regions with substantial local increases of emissions.
How to cite: Ren, Z., Kawai, K., Liu, M., and Matsui, H.: Impacts of Arctic warming on ice nucleating particles from 1981 to 2020: Distributions and contributions of dust, marine organic aerosols, and bioaerosols, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-23242, https://doi.org/10.5194/egusphere-egu26-23242, 2026.
Aerosol-cloud interactions in the Arctic, especially with mixed-phase clouds, remain one of the largest sources of uncertainty in climate projections. The 2024 QuIESCENT workshop, held in Lausanne, Switzerland, gathered researchers from around the world to tackle these challenges and define a collaborative roadmap for future research.
This poster explores the workshop’s central themes, emphasizing the urgent need for continuous, long-term observations of cloud condensation nuclei and ice-nucleating particles, as well as the importance of advanced vertical profiling techniques using cutting-edge platforms like uncrewed aerial systems and tethered balloon systems. The poster highlights how emerging technologies, such as artificial intelligence, machine learning, and next-generation remote sensing tools like the EarthCARE satellite, are revolutionizing our ability to collect and analyze data in this remote and rapidly changing environment.
A key focus will be on the evolving sources of Arctic aerosols, including shipping emissions, wildfires, and microplastics, and their complex impacts on cloud formation and climate feedbacks. The poster will also address the critical role of international collaboration and the inclusion of understudied regions.
By synthesizing the workshop’s outcomes, this poster aims to highlight how these insights can inform upcoming global initiatives, such as the International Polar Year 2032-33, and foster coordinated efforts to reduce uncertainties in Arctic climate projections. Join us to discuss how the scientific community can collectively advance our understanding of Arctic aerosol-cloud interactions and their global climate impacts.
Keywords: Arctic, aerosol-cloud interactions, mixed-phase clouds, field campaigns, remote sensing
How to cite: Coopman, Q., Zamora, L., de Boer, G., Calmer, R., Wadlow, I., Sotiropoulou, G., and Gryspeerdt, E.: Future Directions for Aerosol-Cloud-Precipitation Interaction Research in the Arctic from the QuIESCENT 2024 Workshop, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5075, https://doi.org/10.5194/egusphere-egu26-5075, 2026.
This study investigates aerosol–cloud–radiation interactions over the Arctic using the Weather Research and Forecasting model coupled with chemistry (WRF-Chem) together with an aerosol-aware microphysics scheme. In the atmosphere, aerosols directly affect the radiation budget by absorbing and scattering solar radiation (Jin et al., 2014), and indirectly by modifying cloud albedo and lifetime (Li et al., 2018). Aerosols also act as nuclei for heterogeneous condensation and promote cloud droplet formation; therefore, changes in aerosol number concentration are expected to alter cloud droplet number and size distributions and, in turn, cloud properties (Ramanathan et al., 2001). Also, Aerosol size distribution can play an important role under high aerosol loadings, whereas aerosol composition tends to be much less important, except perhaps under very polluted conditions and low updraught velocities (McFiggans et al., 2006).
More recently, dust sources in the northern high latitudes have received increased attention (Meinander et al., 2022). high-latitude dust is defined as dust emitted from regions north of 50°N (Bullard et al., 2016). Observations and modeling studies suggest that high-latitude dust can act as an efficient ice-nucleating particle (INP), promoting the conversion of cloud droplets to ice crystals. This can strongly reduce the cloud’s liquid water content, lower its albedo, and make the underlying surface more exposed.
Aerosol size distribution strongly controls how many particles can activate as cloud condensation nuclei (CCN) and also affects aerosol optical properties. Therefore, changing particle size, even if all other model settings are kept the same, can change the CCN-active particle population. In mixed-phase clouds, ice formation depends on ice-nucleating particles, and mineral dust is an important source of these particles. To isolate the role of particle size from confounding influences, we conduct one control simulation and a suite of sensitivity experiments in which dust mass is redistributed toward finer versus coarser size bins within a sectional (size-bin) aerosol representation, while keeping the remaining model configuration fixed. Preliminary analyses suggest that changing particle size alone leads to only small changes in cloud properties and radiation, likely because the results are mainly controlled by meteorology (e.g., vertical motion, moisture, and stability) or because the microphysics scheme does not strongly transfer aerosol changes into cloud optical properties and radiative fluxes. Accordingly, we advance a more targeted experimental methodology that explicitly separates CCN and INP pathways. The first step applies direct, controlled perturbations to CCN-relevant aerosol number to generate clean-to-polluted contrasts; the second step independently varies dust INP activity to isolate ice-nucleation pathways; and the framework is configured to distinguish direct radiative effects from indirect (microphysical) effects.
Finally, diagnostics are performed in a regime-based case by stratifying clouds by thermodynamic phase (liquid-dominated versus mixed-phase clouds) and by large-scale forcing (regions of ascent and moisture-flux convergence versus moisture divergence and subsidence). This approach is intended to identify conditions under which aerosol sensitivity is expected to be maximized and to facilitate evaluation against observational and satellite-derived products.
How to cite: Fattahi Masrour, P. and Coopman, Q.: Aerosol–cloud interactions in Arctic mixed-phase clouds under dust size perturbations in a regional chemical weather modeling system (WRF-Chem) , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-3401, https://doi.org/10.5194/egusphere-egu26-3401, 2026.
Low-level clouds play a crucial role in the Arctic climate system, for example by contributing to surface warming. Although many efforts have been made to investigate low-level clouds, there is still a significant in-situ data gap within the atmospheric boundary layer (ABL) and the lower troposphere. While long-term ground-based observatories provide valuable continuous measurements, they cannot resolve the vertical structure of aerosols and clouds.
To address this data gap, five uncrewed aerial systems (UAS) were deployed during two intensive measurement campaigns at the Pallas Atmosphere-Ecosystem Supersite in northern Finland in spring (4–12 April 2025) and autumn (16–30 September 2025). Fixed-wing, vertical take-off and landing (VTOL), and multirotor platforms were operated jointly by the Finnish Meteorological Institute (FMI) and the Technische Universität Braunschweig. In total, 246 measurement flights were conducted, reaching altitudes of up to 2 km above ground level and conducting over 80 hours of in-situ sampling.
The UAS were equipped with different sensors to measure aerosols, including two condensation particle counters with different cut-offs to measure the aerosol particle number concentration, a Partector 2 Pro to measure the size distribution between 10 and 300 nm and a POPS to measure the size distribution between 115 and 3370 nm. In addition meteorological parameters, and cloud droplet properties were also measured. This enables a detailed characterization of the vertical distribution of aerosols and their interaction with the ABL and low-level clouds. These measurements were compared to long-term observations from the nearby ground-based observatory Sammaltunturi. This study demonstrates the value of combining ground-based measurements with UAS profiling when investigating aerosol-cloud interactions.
Preliminary results indicate pronounced seasonal differences. Spring conditions were dominated by new particle formation events associated with long-range air mass transport from the central Arctic. In contrast, autumn measurements were strongly influenced by low-level cloud formation and local aerosol sources. Overall, this campaign demonstrates the added value of UAS observations in improving the understanding of aerosol-cloud interactions in the sub-Arctic and enhancing the interpretability of existing ground-based datasets.
How to cite: Voss, A., Bärfuss, K., Brus, D., Doulgeris, K.-M., Schuchard, M., Düsing, S., Schlerf, A., Wehner, B., and Lampert, A.: Using uncrewed aerial systems at the sub-arctic site Pallas to study aerosol–cloud interactions, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-13579, https://doi.org/10.5194/egusphere-egu26-13579, 2026.
Arctic aerosols undergo a strong seasonal cycle, with higher aerosol mass in the winter and spring from pollution transported from southerly latitudes, and much lower aerosol mass in the summer when wet deposition removes these aerosols from the atmosphere before they can reach the Arctic. The radiation budget in the summer is extremely important since it contributes to surface warming, so the effect of aerosols on cloud properties in summer must be characterized. The clean periods in the summer can affect radiation in two ways: they can lead to new particle formation (NPF) events, followed by particle growth that allow the particles to become active as cloud condensation nuclei (CCN) at moderate supersaturations (<0.3%); and they can lead to CCN-limited periods, when not enough aerosol particles are present to allow clouds to form. This study characterizes the frequency of occurrence of these two regimes to better understand the contributions of aerosols on clouds, and ultimately radiation, in the Canadian Arctic. To accomplish this, aerosol size distributions measured by a scanning mobility particle sizer (10 – 500 nm) were analyzed from the Polar Environment Atmospheric Research Laboratory (PEARL) at Eureka, Nunavut on Ellesmere Island (80N, 86.5W) in the Canadian Arctic Archipelago from 2015 – 2023. Monthly frequency occurrence of days classified as NPF and CCN-limited will be presented, as well as related meteorological conditions (e.g. temperature, relative humidity, boundary layer height). These findings provide an understanding of the importance of these two unique aerosol regimes in the Arctic summer and their potential impact on clouds and radiation.
How to cite: Chang, R., Gauvin-Bourdon, P., Vicente-Luis, A., Fogal, P., Sharma, S., Chan, T., Strong, K., and Hayes, P.: Characterizing the contribution of summer aerosol to cloud formation in the Canadian Arctic, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-15746, https://doi.org/10.5194/egusphere-egu26-15746, 2026.
Mixed-phase clouds on the Northern Slope of Alaska are critical for radiative balance but seem to exist in a delicate balance—often persisting for several days, despite their inherent instability, followed by a sudden dissipation (Morrison et al., 2011). Riming is a highly efficient process for removal of cloud mass and is surprisingly common in the Arctic despite frequent low levels of liquid water path (LWP< 50 g m-2; Fitch & Garrett, 2022). In this work, we evaluate such “enhanced riming” cases in the context of two competing hypotheses: 1) “clean” clouds, with relatively few, larger cloud droplets—leading to a higher riming efficiency (e.g, Tridon et al., 2022); and 2) “polluted” clouds, where a larger number of smaller droplets leads to amplified cloud-top radiative cooling—in turn leading to more intense cloud-scale circulations and lofting of riming particles. We analyze these hypotheses using ground-based Multi-Angle Snowflake Camera (MASC) data coupled with aerosol and LWP measurements at Utqiagvik, Alaska. At cloud level, we use cloud and aerosol measurements from the Chemistry in the Arctic: Clouds, Halogens, and Aerosols (CHACHA) Field Campaign (Fuentes et al., 2025). We first show results from the CHACHA period, 21 February to 16 April of 2022, during which time there was a transition from low-level, long-range transport of “Arctic haze” particles to a more photochemical-dominant new particle formation regime. Beyond the CHACHA period, we also show results from surface-based measurements only for 2021-2024 at Utqiagvik and 2016-2018 at Oliktok Point, Alaska. Initial results suggest that enhanced riming is more common for the polluted clouds cases of the second hypothesis. Additional analysis will help to shed more light on a poorly understood yet important microphysical process that needs more accurate representation in numerical climate and weather models.
How to cite: Afanador, S. and Fitch, K.: Arctic Haze and New Particle Formation Influences on Enhanced Riming Processes in Mixed-Phase Stratiform, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14782, https://doi.org/10.5194/egusphere-egu26-14782, 2026.
Recent studies show that warm and moist air intrusions are major sources of aerosol particles in the Arctic, affecting local radiative impacts by supplying Cloud Condensation Nuclei (CCN). However, their influence on aerosol size modes, CCN, and cloud droplet number concentrations remains poorly constrained. Here, we use long-term aerosol observations from five Arctic observatories to quantify intrusion impacts. We find that intrusions strongly perturb Arctic CCN, especially in summer, when accumulation-mode and CCN concentrations increase markedly at all sites. In winter and spring, two regimes emerge: intrusions reduce number concentrations at sites near 0° longitude (Zeppelin, Villum, Alert) but enhance them near 180° (Tiksi, Utqiaġvik/Barrow), consistent with competing effects of pollution sources and wet scavenging along trajectories. Intrusions also systematically modify cloud droplet number concentration (Nd): Nd increases at all sites in summer, while in winter it increases at Tiksi and Utqiaġvik/Barrow but decreases at Zeppelin, Villum, and Alert. Overall, intrusions are a key regulator of Arctic aerosol and cloud properties and an important component of the evolving Arctic climate system.
Beyond aerosol–cloud number effects, it is unclear how intrusion events modulate cloud optical depth, liquid water content, and precipitation across Arctic sites and seasons. To address this, we will combine cloud and precipitation observations from the year-long Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition with reanalysis data to quantify systematic intrusion-driven changes in liquid water content and precipitation occurrence. Finally, we will use the non-hydrostatic mesoscale Weather Research and Forecasting (WRF) model to examine the sensitivity of mixed-phase cloud lifetime and associated precipitation to intrusion occurrence, providing process-level constraints on how intrusions shape Arctic mixed-phase cloud persistence and hydrometeor production.
How to cite: Dönmez, B., Boyd Pernov, J., Foskinis, R., Calmer, R., Georgakaki, P., Angot, H., Asmi, E., Backman, J., Chan, T., Krejci, R., Massling, A., Skov, H., Tunved, P., Wiedensohler, A., Weinhold, K., Nenes, A., and Schmale, J.: Warm–Moist Intrusions as a Key Regulator of Arctic Aerosols, Clouds, and Precipitation, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18175, https://doi.org/10.5194/egusphere-egu26-18175, 2026.
Carbohydrates are important components of marine organic aerosol particles and may influence Arctic cloud formation and properties, yet their sources and atmospheric fate remain poorly understood. We present the first year-round measurements of combined and dissolved carbohydrates (CCHOaer; DFCHOaer) in aerosol particles collected throughout the annual cycle of the MOSAiC expedition in 2019-2020. CCHOaer were detected in all seasons (0.5-17 ng m⁻³), and contributed between 0.03 and 2.2% (mean 0.3%) to the particulate mass. Their molecular composition was relatively stable and dominated by glucose, xylose, and galactose, with additional presence of uronic acids in summer. Both, CCHOaer and DFCHOaer showed pronounced summer maxima and seasonal variability that partially aligned with chlorophyll-a, nanophytoplankton, and heterotrophic microorganisms, indicating enhanced biological contributions after sea ice melt. The summer increase in DFCHOaer also coincided with warmer temperatures and higher humidity. In winter, the presence of carbohydrates may be sustained by microbial degradation or viral lysis of organic material in under-ice environments. CCHOaer and DFCHOaer concentrations showed no direct correlation to wind speed or air mass origins instead displaying a high variability in summer. The seasonal behavior of CCHOaer in Arctic aerosol particles differed from primary marine tracers like sodium that was associated with direct oceanic sources in summer and blowing snow in winter. This contrast suggests that carbohydrates, while possibly originated from marine biological sources, undergo significant atmospheric modification that overlay direct source signatures. Strong correlations between CCHOaer and low-molecular-weight organic acids further point to photochemical oxidation as an additional driver of secondary carbohydrate processing. CCHOaer displayed seasonal trends similar to warm-temperature ice-nucleating particles and hyper-fluorescent aerosol particles, supporting their role within a broader Arctic bioaerosol particle population. Overall, our results indicate that marine ecosystems provide a continuous source of atmospheric carbohydrates, but their composition is strongly modified by both biotic and abiotic processes, particularly in summer.
Acknowledgement: This work was supported by the DFG funded Transregio-project TRR 172 “Arctic Amplification (AC)3“.
How to cite: van Pinxteren, M., Zeppenfeld, S., Creamean, J., Frey, M., Schmale, J., Heutte, B., Dall´Osto, M., Hoppe, C., Wex, H., and Herrmann, H.: Marine carbohydrates in Arctic aerosol particles – connections to oceanic emissions and in-situ processing, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-2568, https://doi.org/10.5194/egusphere-egu26-2568, 2026.
Marine cold-air outbreaks (MCAOs) in the Arctic lead to the formation of mixed-phase clouds that downwind from the sea ice edge transition from stratocumulus clouds organized as convective rolls to open convective cells. Results from modelling studies of MCAOs suggest that increases in ice nucleating particles (INP), ice crystal number concentrations (Ni) and frozen hydrometeors in general, cause a decrease in cloud water, which can accelerate the cloud transition. In this study, we make use of observations conducted during MCAOs characterized by both high INP concentrations, potentially linked to long-range transport, and low INP concentrations, most likely associated with local sources. We perform quasi-Lagrangian large-eddy simulations of two MCAOs in the Arctic with distinctly different meteorological conditions and investigate the impact of differences in the aerosol and INP concentrations and origin. We examine how perturbations in aerosols, INPs and the predicted cloud ice in the model affect the evolution of the mixed-phased clouds, aerosol processing, and the cloud radiative feedback during these cold air outbreaks.
How to cite: Baró Pérez, A., Plach, A., and Ekman, A.: Comparing large-eddy simulations of marine cold-air outbreaks in the Arctic under contrasting aerosol and ice nucleating particle concentrations and origins., EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14231, https://doi.org/10.5194/egusphere-egu26-14231, 2026.
Sea ice and snow are key interfaces linking the ocean and atmosphere in polar regions, yet their role in driving biogeochemical coupling among halogens, aerosols, and clouds remains incompletely understood. Here, we show that ice-mediated chemical reactions provide an efficient pathway connecting sea ice and snowpack chemistry to atmospheric halogen activation, aerosol formation, and climate-relevant processes in polar environments.
Freezing processes induce strong solute enrichment, pH shifts, and microstructural heterogeneity within sea ice and snow, creating reactive interfacial environments that promote redox and photochemical transformations of iodine and bromine species. Laboratory experiments demonstrate that iodate, bromate, and halide species undergo accelerated reactions in ice involving natural organic matter, iron oxides, and nitrogen oxides, leading to the production of molecular halogens, reactive halogen intermediates, and organohalogen compounds. These ice-phase reactions are substantially enhanced relative to liquid systems and are further amplified under polar irradiation conditions.
Field observations reveal inorganic halogen speciation patterns in snow and sea-ice-influenced environments that are inconsistent with passive deposition alone, supporting the occurrence of active in-ice chemical processing. The resulting release of reactive halogen species facilitates air–ice exchange, contributes to boundary-layer halogen activation, and influences aerosol oxidation pathways, with potential impacts on cloud condensation nuclei and polar cloud formation.
Our findings highlight sea ice and snow as active biogeochemical reactors that couple oceanic halogen reservoirs to the atmosphere. As climate-driven changes in sea ice extent, snow cover, and freeze–thaw dynamics continue, ice-driven halogen chemistry is expected to modulate aerosol–cloud–ocean–sea ice interactions in polar regions, representing a previously underappreciated feedback in the polar climate system.
How to cite: Kim, K.: Freeze-Induced Halogen Redox Chemistry in Sea Ice and Snow Linking Oceanic Sources to Polar Aerosols, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6143, https://doi.org/10.5194/egusphere-egu26-6143, 2026.
Atmospheric mineral dust and black carbon (BC) aerosols play important roles in the Earth’s climate system, yet direct observations over the Southern Ocean (SO) are scarce. In this study, we present the characteristics of airborne water-insoluble particles collected during a cruise of the R/V Shirase in the Australian and Indian sectors of the SO from December 2022 to March 2023. Using a complex amplitude sensor, we measured complex scattering amplitude of individual water-insoluble particles. Based on the measured complex scattering amplitude, which depends on particle composition, size, and shape, we classified into dust-like (0.50–5.0 µm in diameter) and BC-like (0.15–0.50 µm in diameter) particles. The number (mass) concentrations of dust-like and BC-like aerosols were 0.013–9.2 L-1 (0.52–32 ng m-3) and 5.4–2.3×102 L-1 (0.065–2.1 ng m-3), respectively. For dust-like aerosols, the highest concentration was observed in a region closest to Australia in this cruise, indicating strong influence of the emission from mid-latitude continents. Furthermore, a sample collected nearest to the Antarctic coast exhibited relatively high dust-like aerosol concentrations than that collected in most offshore regions away from both mid-latitude and Antarctic continents, suggesting that the Antarctic continent might be a potential source of dust aerosols. For BC-like aerosols, their concentration showed a clear latitudinal gradient, decreasing with distance from mid-latitude sources even close to the Antarctic coast.
How to cite: Yoshida, A., Tobo, Y., Kobayashi, H., Adachi, K., Moteki, N., and Inoue, J.: Shipborne Measurements of Mineral Dust and Black Carbon Aerosols over the Southern Ocean in the Austral Summer, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8683, https://doi.org/10.5194/egusphere-egu26-8683, 2026.
Early studies from the 90’s on INPs in the Southern Ocean (SO) have already revealed lower INP concentrations in the SO region than in other marine regions. This feature was confirmed in recent measurements and modeling exercises, with implications on our ability to model the cloud persistence in the Southern Ocean. The INP populations found in these regions were commonly organic and heat-stable, which contradicts the hypothesis of microorganism promoting ice nuclei formation. Here we present results from the POLARCHANGE ship campaign where samples of Southern Ocean seawater were taken and analyzed across a latitudinal gradient down to the vicinity of sea ice formed in the Weddell Sea. In addition, samples of Sea Ice cores were collected and ice nuclei particle (INP) concentrations were analyzed at various depths of the Sea Ice cores, and within brine samples. The comparison between Sea Ice, brine and Seawater INP concentrations latitudinal gradient, in relation with the biogeochemical properties of these different compartments provides insight into processes that could explain the very low INP concentrations in the SO and polar atmosphere.
How to cite: Freney, E., Sellegri, K., Crabeck, O., Rocchi, A., Delille, B., Bouvier, L., Bardet, E., Dall'Osto, M., and Simo, R.: Ice Nuclei properties in seawater, sea ice and brine from the Southern Ocean, Weddell Sea and Antarctic Peninsula: on the potential anti-freezing properties of polar microbiota, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-13131, https://doi.org/10.5194/egusphere-egu26-13131, 2026.
The sensitive Arctic environment is affected by rapid climate change. Melting of glaciers and permafrost drives large changes in the transport of organic matter to the ocean, affecting e.g. macroalgae and phytoplankton. This also affects levels and chemical composition of atmospheric organic aerosols through formation of sea spray aerosols, as well as exchange across the sea-air interface of reactive volatile organic compounds, which are photochemically oxidized, forming products contributing to formation and growth of atmospheric aerosols. Aerosols influence climate through direct interaction with radiation and by affecting the formation and lifetime of clouds. Cloud feedbacks have both warming and cooling effects on the climate, however climate models for the Arctic region largely disagree about the direction of this feedback.
The presentation will provide an overview of our recent investigations of organic compounds in Arctic aerosols and dissolved organic matter (DOM) in Arctic seawater.
Aerosols and seawater samples were collected in the Fram Strait during the ”Atmospheric rivers and the onset of Arctic melt” (ARTofMELT 2023) and at Disko Bay, Greenland (69°2'N, 53°3'W) during spring and summer 2023. Furthermore, aerosol samples were obtained from Villum Research Station (81.6oN, 16.7oW). After sample preparation, both aerosol and water samples were analysed using ultra-high-performance liquid chromatography coupled to high-resolution Orbitrap mass spectrometry (UHPLC-Orbitrap MS).
Molecular tracers of biogenic secondary organic aerosols (BSOA) derived from isoprene and monoterpenes were quantified using authentic standards in all aerosol samples. The levels and composition of BSOA tracers provide insight into the origin of Arctic organic aerosols, from both regional sources and long-range transport. In one aerosol sample from Disko Bay, the concentration of BSOA was highly elevated due to long-range transport of air masses from the boreal zone. A series of dicarboxylic acids were also quantified in both aerosol and DOM to investigate the marine origin of these compounds. Furthermore, non-targeted analysis was employed to provide broader insight into the overall organic composition of both aerosols and DOM.
This work was supported by the Novo Nordisk Foundation, the Swedish Polar Research Secretariat, the Swedish Research Council (VR), the Knut and Alice Wallenberg Foundation, the Carlsberg Foundation, and the Danish National Research Foundation (DNRF 172) through the Center of Excellence for Chemistry of Clouds.
How to cite: Glasius, M. and the The Organic Compounds in Aerosols and Seawater in the Arctic Team: Exploring the Molecular Landscape of Organic Compounds in Aerosols and Seawater in the Arctic during spring and summer, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14390, https://doi.org/10.5194/egusphere-egu26-14390, 2026.
Using model output from the Radiative Forcing Model Intercomparison Project (RFMIP), endorsed by the sixth Coupled Model Intercomparison Project 6 (CMIP6), we investigated the impact of aerosols on the Arctic climate (averaged over the region north of 66°N) during winter. The average of these models shows that the present-day aerosols (as of the year 2014) result in a positive aerosol effective radiative forcing (ERFaer) of approximately 0.14 W m–2 in the Arctic during winter, relative to pre-industrial conditions defined as those of the year 1850. This positive ERFaer is associated with enhanced aerosol loading through strong transport from Eurasia and adjoining regions, causing the Arctic region to warm by up to 1 K in the present-day compared to the pre-industrial conditions. The Arctic warming attributed to aerosols also significantly affects climate variability, particularly the Arctic Oscillation (AO). Present-day aerosols resulted in a positively skewed distribution of the Arctic Oscillation index (AOI) compared to the control simulation, reflecting a shift toward more frequent positive AO phases associated with negative sea level pressure (SLP) anomalies across the northern Atlantic, Pacific, and Eurasian regions, and positive SLP anomalies over northern North America. Additionally, the transient experiment, which includes time-varying aerosol emissions, is used to investigate the sensitivity of Arctic winter climate to the aerosol enhancement, based on low and high aerosol scenarios. During the high aerosol scenario, warming in near-surface air temperature (SAT) is concentrated over the Arctic region, reaching approximately 1 K, while less warming is simulated in the low aerosol scenario. The AOI distribution is positively skewed in both aerosol scenarios, indicating that changes in aerosol concentrations influence the AO. However, the skewness is weaker under the high aerosol scenario compared to the low aerosol case, suggesting that stronger aerosol forcing tends to stabilize the AO and limit its variability. Nevertheless, increased sensitivity of the AO to aerosol can lead to extreme weather, particularly warmer winters in the Arctic, in contrast to most of the Northern Hemisphere, regardless of the AO phase. Our analysis also suggests that aerosol enhancement contributes to a shift in the jet stream’s position. Furthermore, the lapse rate feedback (LRF), a contributor to the Arctic amplification, also shows an increase due to aerosol enhancement. This indicates that both the strength and magnitude of the LRF are sensitive to aerosol concentrations, which may further intensify Arctic warming/amplification.
The results have been published:
Al Hajjar, K., Dipu, S., Quaas, J., Linke, O. and Haustein, K. (2025) ‘Exploring the Sensitivity of Arctic Winter Climate to Aerosol Loading as Simulated in CMIP6’, Tellus B: Chemical and Physical Meteorology, 77(1), p. 20–40. Available at: https://doi.org/10.16993/tellusb.1885.
How to cite: Al Hajjar, K.: Exploring the Sensitivity of Arctic Winter Climate to Aerosol Loading as Simulated in CMIP6, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11218, https://doi.org/10.5194/egusphere-egu26-11218, 2026.
Aerosol particles are a key player in the Arctic climate as they act as a surface for cloud droplet condensation and ice nucleation, subsequently affecting the radiative properties of clouds. In the Arctic, interactions between the ocean, sea ice, and atmosphere strongly influence the production and transformation of aerosol particles, but the mechanisms controlling particle number concentrations and size distributions are still poorly constrained. Marine organic gas-phase compounds are known to play an important role in initiating new particle formation and sustaining particle growth to climatically relevant sizes with e.g. potential to serve as cloud condensation nuclei. However, substantial knowledge gaps remain in our understanding of their sources and processes, and quantifying the role of secondary aerosol formation and growth in shaping cloud-active aerosol populations remains a challenge.
Spring and the important start of the melt period is a particularly under-sampled season over the Arctic pack ice, due to difficult ice conditions leading to logistic challenges. In 2023, the ARTofMELT (Atmospheric rivers and the onset of sea ice melt) expedition on board the Swedish icebreaker Oden set out to cover this crucial time period, when the aerosol population transitions from haze conditions dominated by long-range transport to being characterized by local sources and corresponding processes.
Here, we present measurements of a large-scale aerosol growth event over the Arctic pack ice, in the middle of the seasonal transition into summer. The growth event was preceded by a storm, followed by long-lasting fog, and sustained over several days and across hundreds of kilometers. By combining the broad range of aerosol instrumentation onboard with data from nearby monitoring stations at Villum (North Greenland) and Zeppelin (Svalbard) observatories, trace gas measurements, air source analysis (ie. water vapor isotopes and air parcel modeling), and regional model simulations, we investigate factors defining the origin of the event and its potential impact.
How to cite: Kojoj, J., Zang, C., Fellin, D., Haberstock, L., Thomsen, L. D., Schmidt, J. S., Da Silva, A., Lapere, R., Kopec, B., Welker, J. M., Glasius, M., Gilardoni, S., Santl-Temkiv, T., Willis, M., Krejci, R., and Zieger, P. and the Villum Research Station science team: A regional aerosol growth event during the onset of sea ice melt, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18302, https://doi.org/10.5194/egusphere-egu26-18302, 2026.
The Arctic is warming at more than twice the global average rate, a phenomenon known as Arctic amplification (Rantanen et al., 2022). In addition to greenhouse gases, short-lived climate forcers play a critical role in modulating Arctic climate through their impacts on radiation, cloud properties, and the surface energy balance (e.g. AMAP, 2015, 2021). Among these forcers, elemental carbon (EC) is of particular importance due to its strong light-absorbing properties and its ability to reduce surface albedo when deposited on snow and ice. Furthermore, aged EC particles transported to the Arctic can act as cloud condensation nuclei, influencing cloud microphysical processes and thereby modifying Arctic radiative forcing and climate feedbacks.
In this study, we investigate long-term trends in EC concentrations and their potential drivers in the high Arctic using 16 years of continuous EC measurements from the Villum Research Station in northeast Greenland. We combine in situ observations with Lagrangian transport modelling and back-trajectory analyses to assess the relative contributions of changes in source-region emissions, transport pathway variability, and wet scavenging processes to the observed EC trends. Robust non-parametric statistical methods are applied to assess monotonic trends over the full observational period and before 2020, enabling a systematic comparison between the declining and stagnating phases. This integrated observational–modelling framework provides new constraints on the processes controlling EC variability in the Arctic and advances our understanding of how anthropogenic emission reductions are reflected in Arctic atmospheric composition under a rapidly evolving climate.
How to cite: Zhang, L., Skov, H., Massling, A., Dall’Osto, M., Evangeliou, N., Che, H., Jensen, B., and Im, U.: Long-term trend of elemental carbon in the high Arctic and its potential drivers, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17708, https://doi.org/10.5194/egusphere-egu26-17708, 2026.
Primary marine organic aerosol (PMOA) constitutes an important fraction of the aerosol population over remote oceanic regions and plays a relevant role in aerosol–cloud–climate interactions. In the Arctic, ongoing sea-ice retreat and intensified summer ice loss are expected to enhance marine aerosol emissions. Here, we employ an extended version of the aerosol–climate model ECHAM6.3-HAM2.3 to examine the spatial distribution and long-term temporal evolution of PMOA emissions and transport in the Arctic for the period 1990–2019, accounting for changing climatic and sea-ice conditions. Marine biogeochemical fields are provided by the offline model FESOM2.1-REcoM3, from which three aerosol-relevant biomolecular species groups - polysaccharides (PCHO), amino acids (DCAA), and polar lipids (PL) - are represented. Their transfer from the ocean to the atmosphere is parameterized using OCEANFILMS, recently implemented in ECHAM6.3-HAM2.3 to enhance the marine emission scheme.
The model results indicate that PMOA emission fluxes are primarily controlled by marine biological activity and sea-salt production, the latter mainly depending on near-surface winds. Biomolecular concentrations show limited variability in equatorial regions but pronounced seasonal cycles toward high latitudes. In seawater, PCHO dominates the simulated organic pool, followed by DCAA and PL. In contrast, PL contributes the largest fraction to aerosol-phase organic matter due to the comparatively strong air-seawater affinity of lipids. Arctic PMOA emissions and atmospheric transport peak between May and September, coinciding with the phytoplankton bloom and the seasonal sea-ice minimum. Substantial regional differences are evident in the timing of biomolecule production and aerosol emissions across the Arctic. Simulated PMOA seasonality agrees reasonably well with available ground-based observations, given the uncertainties in both measurements and model assumptions.
Over the 30-year period, accumulated Arctic aerosol emissions and burdens increased by at least 7% and 4%, respectively, when comparing the first and second halves of the study period. Summer (June–August) trend analyses reveal a pronounced decline in sea ice that is associated with increasing concentrations of organic biomolecules in inner Arctic waters. Positive PMOA emission anomalies have become more frequent over the past 15 years, indicating a sustained upward trend. On average, PMOA production has increased by 0.8% per year since 1990, with changes varying among biomolecular groups and Arctic subregions.
How to cite: Heinold, B., Leon-Macros, A., van Pinxteren, M., Zeppenfeld, S., Zeising, M., and Bracher, A.: Spatial patterns and long-term trends of primary marine organic aerosol in the Arctic, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-13679, https://doi.org/10.5194/egusphere-egu26-13679, 2026.
Atmospheric aerosols often contain surface‐active organics, which reduce surface tension and
enhance cloud droplets activation. This effect is often neglected in the application of Köhler theory where a
constant surface tension equivalent to pure water is assumed. Using a cloud parcel model, we evaluated the
impact of four representative surface‐active organics, humic‐like substances (HULIS), sodium dodecyl sulfate
(SDS), cis‐pinonic acid, and dicarboxylic acids, on cloud condensation nuclei (CCN) activation under varied
atmospheric conditions. Our results indicate that HULIS significantly enhance CCN activation, particularly at
high aerosol concentrations, low updraft velocities, and small particle sizes. SDS, cis‐pinonic acid, and
dicarboxylic acids also increase activation but to a lesser degree. The surface activity of HULIS has a stronger
influence on CCN activation than its hygroscopicity, with particle size being the most sensitive parameter. This
study emphasizes the need to incorporate surface‐active organics into climate models to improve the prediction
of aerosol‐cloud interactions.
How to cite: Lin, G.: Modeling impacts of surface-active organics on CCN activation, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11848, https://doi.org/10.5194/egusphere-egu26-11848, 2026.
Posters virtual: Tue, 5 May, 14:00–18:00 | vPoster spot 5
EGU26-12630 | ECS | Posters virtual | VPS3
Closed to Open-Celled Mixed-Phase Cloud Transition Over the Nordic Seas Under High Aerosol LoadingTue, 05 May, 14:18–14:21 (CEST) vPoster spot 5
A closed to open-celled transition of mixed-phase clouds within a marine cold air outbreak (MCAO), driven by an occluded cyclone over the Nordic Seas, is interrogated with data acquired during the Cold Air Outbreak Experiment in the Sub-Arctic Region (CAESAR) field campaign on 29 February 2024. The understanding of these transitions is a challenge for numerical prediction models due to their small scale but important for weather and climate prediction, as open celled conditions have stronger updrafts supporting locally high precipitation rates along with a lower cloud fraction (lower albedo) than closed celled conditions. Measurements indicate that a stratiform (closed cell convective) cloud deck with cloud top heights of ~1230 m and liquid water paths (LWP) of ~130 gm-2, within a boundary layer with aerosol number/CCN surpassing 600 cm-3, deepen to heights of ~1520 m with LWPs of ~270 gm-2 over 250 km of fetch, before transitioning into an open-celled convective structure with cloud tops reaching up to 2220 m. Cooling free tropospheric temperatures with fetch, which reduce the inversion strength thereby enhancing growth by entrainment may encourage boundary layer growth. Open-cells are more glaciated than closed-cells with mean LWPs falling from 270 gm-2 to 80 gm-2 across the transition, however isolated peaks of LWP within updrafts of open cells occasionally surpass 500 gm-2. Minimal secondary ice production (SIP) is observed in closed cells with ice nucleating particle and ice number concentrations ~2 L-1 with cloud temperatures between -20oC and -15oC. In open cellular convection (cloud temperatures between -22oC and -15oC), ice number concentrations reach ~10 L-1 indicating SIP. High aerosol concentrations are hypothesized to support the maintenance of closed-celled convection, with 80% of drops smaller than 10 μm reducing the riming efficiency. Small droplets also limit the production of freezing drizzle, which is hypothesized to limit the potential of SIP due to freezing/fragmentation within closed cell convection. Only after aerosol concentrations are depleted through scavenging and/or entrainment are SIP processes able to become more effective and precipitation particles able to grow large and dense enough to reach the surface and form cold pools breaking up the cloud deck. Plumes of warm moist air lifting off the ocean surface, juxtaposed with cold pools and entrainment events penetrating to the surface are documented using the Multi-function Airborne Raman Lidar (MARLi) in the first observations of its kind.
How to cite: Ephraim, S., Zuidema, P., Bansemer, A., Cai, L., Cruikshank, O., Evengeliou, N., French, J., Geerts, B., Grasmick, C., Massling, A., McFarquhar, G., Noel, G., Petters, M., Rosky, E., Skov, H., Snider, J., Tatro, T., Wang, Z., Woods, S., and Zhang, L.: Closed to Open-Celled Mixed-Phase Cloud Transition Over the Nordic Seas Under High Aerosol Loading, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12630, https://doi.org/10.5194/egusphere-egu26-12630, 2026.
