The observations were made during field campaigns in autumn 2021 and spring 2022 near Kongsfjord, close to Ny-Ålesund, the world’s northernmost permanently inhabited settlement. Researchers from the Leibniz Institute for Tropospheric Research, Leipzig University, the University of Cologne, the Alfred Wegener Institute, the Max Planck Institute for Marine Microbiology, the University of Oldenburg and the University of Bremen collected air samples at elevations between 300 and 1,000 metres. To reach those heights, the team used BELUGA, a 12-metre-long tethered helium balloon capable of carrying scientific instruments and sampling equipment into the lower atmosphere. The balloon had previously been used during the MOSAiC expedition, when the research icebreaker Polarstern drifted through the central Arctic for an entire year.

The atmosphere above the Arctic is closely connected to the surface ocean. When waves break and bubbles burst, tiny droplets of seawater are ejected into the air as sea spray aerosol. These particles contain familiar inorganic salts, primarily sodium and chloride, but they also carry a less visible biological cargo. The ocean’s surface film and underlying seawater contain organic compounds produced by marine organisms, including carbohydrates and highly branched polysaccharides. These molecules can be released by phytoplankton, bacteria and other microorganisms, becoming embedded in or attached to sea spray particles. Once airborne, the particles can be transported by winds, altered by chemical reactions and incorporated into clouds.

The new measurements are important because marine carbohydrates had previously been identified mainly in seawater, sea-surface microlayers and air close to the ocean. Researchers had little direct evidence showing how far these compounds could rise through the atmosphere. The team compared samples gathered by BELUGA at different altitudes with samples of seawater and surface film collected in Kongsfjord. This combination allowed the scientists to link atmospheric material with a nearby marine source and to trace the vertical distribution of sea spray constituents. The results indicate that ocean-derived carbohydrates are not confined to the immediate vicinity of the water surface, but can be carried into layers of the lower troposphere relevant to cloud development.

That vertical transport matters because sea spray particles can influence cloud microphysics. Clouds are not simply collections of water droplets; their formation and evolution depend on the particles around which water vapour condenses or freezes. Some aerosol particles act as cloud condensation nuclei, encouraging the formation of liquid droplets. Others can serve as ice-nucleating particles, triggering the formation of ice crystals at temperatures where freezing might otherwise be unlikely. Ice formation changes the size and lifetime of cloud particles, affects precipitation and alters how clouds reflect incoming sunlight and emit heat back toward space.

Marine polysaccharides may be especially significant as ice-nucleating material. Earlier laboratory and field research led by TROPOS found that the ice-nucleating activity of sea spray particles is strongly influenced by the polysaccharides they contain. Model simulations indicated that these compounds are particularly relevant between approximately –20 and –15 degrees Celsius, a temperature range common in clouds over remote ocean regions. In such locations, land-derived ice-nucleating particles may be scarce, leaving marine aerosols with a greater potential influence on cloud ice formation. If these particles reach cloud layers, even in small quantities, they could help determine whether a cloud contains supercooled liquid water, ice crystals or a mixture of both.

The study also points to an unexpected possibility: some of the sugars found in the atmosphere may not have come directly from the sea. Laboratory and field observations suggest that chemical and biological activity inside humid air masses and clouds can transform existing molecules or generate additional carbohydrate-like compounds. In clouds containing abundant water and microorganisms, biological metabolism could contribute to the formation of these substances. The evidence is still preliminary, but it raises the prospect that clouds are not passive atmospheric containers. Instead, they may function as reactive environments in which marine organic matter is modified, recycled or even newly produced as air moves above the ocean.

This possibility adds biological complexity to the Arctic climate system. The region is warming faster than the global average, and its sea ice cover is retreating, particularly during the summer minimum. Open water exposes a larger surface area to wind and wave action, potentially increasing the production of sea spray aerosol. At the same time, a warmer atmosphere can hold more water vapour and may support changes in cloud cover, precipitation and atmospheric chemistry. More marine particles entering the atmosphere could alter the reflectivity, thickness and persistence of Arctic clouds. The direction and magnitude of the overall climate effect will depend on particle composition, altitude, season, cloud temperature and whether the particles promote liquid droplets or ice.

The researchers describe their measurements as a first direct link between marine sugars in the Arctic ocean and their presence at multiple atmospheric heights. However, the observations do not mean that every sea spray particle becomes a powerful climate agent, nor do they establish a single, simple effect on Arctic warming. Atmospheric particles are rapidly diluted, chemically transformed and mixed with material from land, snow and distant regions. The team therefore sees the measurements as a missing piece of a much larger puzzle. Future studies will need to determine how long marine carbohydrates survive in the atmosphere, how efficiently they trigger ice formation under real cloud conditions and how much they contribute to regional radiation and precipitation patterns.

The next major test may come far from Svalbard. The BELUGA team plans to collect comparable observations during Polarstern expeditions associated with Antarctica-Insync in 2028, targeting the Southern Ocean, where sea spray and biological activity are also intense but where equivalent vertically resolved measurements remain scarce. Comparing the Arctic and Antarctic could reveal whether marine carbohydrates are a widespread feature of polar atmospheres or a process strongly shaped by local conditions. For now, the Arctic observations deliver a striking message: the ocean’s influence on climate does not stop at the waterline. Waves, microbes, sugars and salt can rise into the sky, enter clouds and help shape the frozen world’s changing climate.

Subject of Research: Not applicable

Article Title: Marine carbohydrates and other sea spray aerosol constituents across altitudes in the lower troposphere of Ny-Ålesund, Svalbard

News Publication Date: 27-May-2026

Web References: https://doi.org/10.5194/acp-26-7235-2026

References: Atmospheric Chemistry and Physics, DOI: 10.5194/acp-26-7235-2026

Image Credits: André Ehrlich, Leipzig University

Keywords: Arctic climate, sea spray aerosol, marine carbohydrates, atmospheric science, cloud formation, ice-nucleating particles, sea ice loss, Svalbard, Ny-Ålesund, BELUGA balloon, marine microbiology, cloud microphysics

The essence of this breakthrough lies in laser-induced fluorescence, a sophisticated technique that identifies aerosol particles by their unique glow when irradiated with specific wavelengths of laser light. Unlike standard lidar technologies, which rely on backscattered laser light and suffer from ambiguity when differentiating aerosol types, fluorescence lidar exploits the intrinsic spectroscopic fingerprint of organic compounds and biomass burning residues. This enables the unambiguous identification of volatile smoke aerosols, even when present in optically thin layers at altitudes as high as 10 kilometers.

The innovative fluorescence channel was appended to the MARTHA lidar system in August 2022. It utilizes an interference filter centered at 466 nanometers to isolate fluorescence emissions from atmospheric particles. Because fluorescence signals are intrinsically weak and can be easily drowned out by solar radiation, these measurements are constrained to nocturnal periods with minimal background noise. Despite the challenges, the researchers amassed over 250 hours of fluorescence observations across 50 measurement sessions from August 2022 to October 2023, yielding unprecedented insight into atmospheric aerosol dynamics.

One of the pivotal revelations from these observations is the frequent detection of thin, elevated smoke layers stemming from massive forest fires in Canada during the spring and summer of 2023. These fires, concentrated in the provinces of Alberta and British Columbia, emitted vast clouds of biomass smoke that were transported by prevailing westerlies to European skies. The fluorescence lidar technique enabled the precise detection of these smoke layers, some exceeding two kilometers in vertical extent, demonstrating pronounced fluorescence signals that betray their biomass burning origin. This discovery challenges prior understandings that largely underestimated the range and impact of transcontinental wildfire aerosols.

Conventional aerosol detection methods encountered difficulties resolving these tenuous layers. Prior to the fluorescence method, many such layers in the upper troposphere appeared transparent or clean, lacking significant backscatter signals. However, the fluorescence data revealed robust aerosol presence at altitudes of 5 to 10 kilometers, layers that would have otherwise gone unnoticed. These findings underscore the critical role of fluorescence lidar in enhancing atmospheric profiling resolution and aerosol characterization, especially in the upper atmospheric regions where direct sampling remains prohibitively challenging.

The climatic implications of these discoveries are profound. Aerosol particles act as cloud condensation nuclei (CCN) and ice nucleating particles (INPs), thereby influencing cloud formation, lifetime, and radiative properties. Particularly significant are cirrus clouds, which form at high altitudes and contain ice crystals that strongly affect the planetary radiation budget. The study observed instances where cirrus clouds were located directly beneath or embedded within smoke layers identified by the fluorescence channel. This spatial co-location supports emerging hypotheses that smoke particles from wildfires might facilitate heterogeneous ice nucleation in cirrus clouds, potentially altering their microphysics and subsequent climate impacts.

Previous research had deemed forest fire smoke inefficient as ice nuclei at temperatures above -30°C, typically attributed to mineral dust and other aerosols. However, the fluorescence lidar observations from Leipzig provide empirical evidence suggesting that smoke aerosols can act as effective ice nuclei under certain conditions. This insight invites renewed scrutiny into aerosol-cloud interactions in the upper troposphere, emphasizing the necessity to reconsider wildfire smoke’s role in modulating cloud formation processes at large scales.

Technically, the MARTHA lidar system distinguishes itself through its multi-wavelength laser emissions at 355, 532, and 1064 nanometers, combined with an 80-centimeter diameter primary mirror that enhances signal collection efficiency. The backscattered light is analyzed through polarization and wavelength-dependent scattering characteristics to infer particle properties. Despite this advanced setup, differentiating between aerosol types like volcanic sulfates, urban pollution, or biomass smoke remained challenging due to overlapping scattering profiles. The addition of the fluorescence channel fills this critical gap, providing a molecular signature that elevates the classification accuracy of aerosol types remotely.

The incorporation of fluorescence lidar into routine atmospheric observations promises to revolutionize the detection of subtle but climatically significant aerosol layers. The Leipzig team’s case studies showcase how this method identifies aerosol structures associated with intense wildfire events far beyond regional boundaries. Their data suggests that the atmosphere over Europe’s upper troposphere may be more polluted than previously thought during wildfire seasons—a realization with far-reaching implications for climate modeling and air quality assessments.

Future developments are already underway to expand the capabilities and temporal coverage of fluorescence lidar observations. Since late 2023, the MARTHA system has been undergoing a comprehensive modernization, including the installation of a more powerful laser and a 32-channel spectrometer. These enhancements will enable higher spectral resolution and sensitivity, facilitating the measurement of aerosol layers extending into the lower stratosphere. According to Albert Ansmann of TROPOS, these improvements will allow for sustained, detailed aerosol monitoring over Central Europe, capturing both volcanic and wildfire aerosol trends vital for understanding climate evolution.

The ongoing research constitutes a central pillar of the Leibniz ScienceCampus ‘BioSmoke,’ an interdisciplinary initiative launched in autumn 2024 to unravel the complex interactions between biomass burning aerosols, biogenic particles, and atmospheric processes. The fluorescence lidar data serves as a cornerstone for this collaborative network, supporting studies on particle emission, long-range transport, and aerosol-cloud coupling mechanisms with unprecedented clarity and precision.

In conclusion, the integration of laser-induced fluorescence into ground-based lidar systems represents a transformative step forward in atmospheric science. By enabling the detection of invisible aerosol layers and unraveling their interplay with cirrus clouds, this technology equips scientists with a powerful toolset to decode aerosol-mediated climate effects. As wildfire activity intensifies globally due to climate change, understanding smoke aerosols’ nuanced roles in cloud physics and radiative forcing becomes ever more critical. TROPOS’s pioneering work thus not only sharpens our scientific lens but also enriches our predictive capabilities regarding climate dynamics in a changing world.

Subject of Research: Not applicable

Article Title: Invisible aerosol layers: improved lidar detection capabilities by means of laser-induced aerosol fluorescence

News Publication Date: 9-Apr-2025

Image Credits: Benedikt Gast, TROPOS

Keywords: fluorescence lidar, aerosol detection, biomass smoke, forest fires, atmospheric aerosols, cirrus clouds, ice nucleating particles, MARTHA lidar, aerosol-cloud interactions, upper troposphere, laser-induced fluorescence