PICO
While extensive research has been dedicated to characterizing the cryo-, litho-, hydro-, and phyllo-spheres as microbial habitats, studies on atmospheric microorganisms have largely focused on their abundance, diversity, and potential climatic and sanitary implications. However, the atmosphere is not merely an inert medium but instead hosts airborne living cells that both influence and are influenced by biological, chemical, and physical processes, contributing to the intricate web of life on our planet.
Understanding microbial life in the atmosphere is essential for deciphering drivers of atmospheric composition, processes, and biogeochemical cycles. Atmospheric microorganisms are closely interlinked with surface habitats and can shape local, regional, and global microbial biodiversity and biogeography. To develop a more complete understanding of the planet’s microbiome, it is therefore critical to identify the chemical, physical and biological factors that shape the diversity, activity, and functioning of atmospheric microbial populations. Such factors include emission and deposition, exposure and response to atmospheric stressors (e.g. oxidants, water and nutrient availability), and the intrinsic traits of the microorganisms themselves.
This session will provide an interdisciplinary platform for all atmospheric scientists, biogeoscientists, microbiologists, and others interested in aerial transport of living microorganisms, microbial processes in the atmosphere, and their feedbacks on the Earth’s surface systems (water, soil, vegetation, ice). We welcome contributions that advance understanding of atmospheric microbiome, its interactions with the atmosphere and surface environments, and the processes that shape microbial diversity, concentrations, interactions, survival, dispersal, and functioning.
PICO: Tue, 5 May, 08:30–10:15 | PICO spot 5
Microorganisms play a significant role in ecological and geochemical processes in aquatic ecosystems, which may also impact water quality and ecosystem health. Understanding the ecological dynamics and evolution of microbial populations in terrestrial water bodies is crucial for evaluating their resilience and adaptability to environmental changes driven by climate change and anthropogenic activities. This research examines inter-environmental connectivity of microorganisms across different terrestrial water bodies to elucidate potential ecosystem implications under changing climatic conditions. To study aerial transmission, connectivity, and microbial survivability, air samples were collected from different water bodies across Israel, including the Dead Sea, Lake Kinneret, and the Mediterranean Sea, using two different air sampling methods and processed using culture-dependent and independent techniques. We will present our findings on airborne microbial dispersal patterns, diversity, and abundance, focusing on aerial transport, viability, and subsequent adaptations. Additional results on bacteria-phage lysogeny in the aerosolized bacterial fraction will be presented, and implications discussed. Our results demonstrate a high presence of viable aquatic bacteria in air samples from various water bodies under different growth conditions, highlighting their adaptability and resilience to environmental changes.
Keywords: Aerial transport, microbial connectivity, climate change, aquatic environments.
How to cite: Shrivastava, V., Weinstock, A., Avrani, S., Ninio, S., Beja, O., Gophna, U., Carmel, Y., and Lang-Yona, N.: Aerial Pathways of Microbial Connectivity Between Waterbodies, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-1986, https://doi.org/10.5194/egusphere-egu26-1986, 2026.
Microbes contained in bioaerosols are a significant component of organic aerosols owing to their unique biological characteristics, which pose health risks and have undeniable meteorological effects. However, the diurnal variation and health risks of microbes in PM2.5 and their responses to atmospheric factors are not well understood. In this study, we conducted a high-time-resolution analysis of near-surface atmospheric microbial communities in PM2.5 at an urban site in Beijing, focusing on microbial composition, seasonal and diurnal distribution patterns, and feedback mechanisms of microbes to environmental factors during typical PM2.5 pollution episodes across different seasons. Additionally, the effects of snowfall on airborne microbes were investigated. This study revealed distinct seasonal and environmental dynamics in atmospheric fungal and bacterial communities. Fungi exhibit stronger seasonal sensitivity and are primarily influenced by meteorological factors, whereas bacteria display consistent temporal heterogeneity driven by fixed emission sources and environmental resilience. Niche differentiation occurred between fungi and bacteria in autumn, whereas summer bacterial communities were notably affected by ozone. Key bacterial genera are reliable biological markers of pollution. The composition of PM2.5, rather than its concentration, significantly affects microbial communities, with bacteria being more susceptible to the formation of secondary inorganic aerosols. The presence of pathogenic microbes in the atmosphere cannot be overlooked. Pathogenic microorganisms show temporal heterogeneity, with fungal pathogens being more diverse but inhibited by SO2 and OC, whereas pathogenic bacteria thrive in cleaner conditions. Snowfall does not efficiently remove airborne microbes but acts as a depositional sink for atmospheric micro-organisms. This study provides a profile of microbial communities in atmospheric aerosols during typical pollution periods and offers a new perspective for understanding the health effects associated with PM2.5 exposure.
How to cite: Zhang, S., Wang, N., Chen, X., Duan, F., Ma, Y., Zhang, Q., Zhu, L., Jiang, J., Wang, S., and He, K.: Environmental sensitivity and resilience of airborne bacteria and fungi with time-scale variation under stress of air pollution and snowfall, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-4593, https://doi.org/10.5194/egusphere-egu26-4593, 2026.
Aerobiological studies have traditionally focused on near-surface sampling and horizontal biogeographic patterns, while vertical microbial structuring within the atmospheric boundary layer (ABL) remains poorly characterized. This knowledge gap is largely due to logistical constraints, including limited accessibility, the need for aerial platforms, and technological challenges in collecting sufficient biomass over short sampling periods.
Here, we present an integrated approach to investigate airborne microbial communities across different levels of the ABL in a coastal Antarctic environment. Microbial samples were collected simultaneously at lower and higher atmospheric levels using aerial and ground-based platforms, and microbial community composition and abundance, as well as morphometry were analysed using metabarcoding and microscopy-based techniques. The study was conducted at a low-orography coastal site in Antarctic Peninsula, what is representative of air masses from the Southern Ocean, and supported by atmospheric observations and air-mass trajectory analyses.
Our results reveal a clear vertical differentiation in airborne microbial communities. Air sampled at higher atmospheric levels showed microbial communities with reduced diversity and distinct taxonomic signatures compared to those closer to the surface, consistent with selective processes acting during vertical transport and atmospheric residence. Samples from near-surface showed comparatively more homogeneous communities, reflecting strong mixing of local biological sources, whereas communities from higher-altitude samples exhibited greater variability among the samples, influenced by broader-scale atmospheric transport. Despite these differences, partial overlap in community composition between atmospheric layers suggests vertical connectivity within the ABL. Variations in microbial abundance and morphometric cell characteristics further support the role of atmospheric structure and stability in shaping airborne microbial assemblages.
How to cite: Galbán, S., Justel, A., González, S., Sanz, P., Bañón, M., Higuera, J. A., Méndez, J., Kim, W. Y., and Quesada, A.: Vertical profiling of airborne microbial communities across the atmospheric boundary layer, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7534, https://doi.org/10.5194/egusphere-egu26-7534, 2026.
The number of aerobiological studies is increasing and whilst patterns are starting to emerge, it is also clear that the results tend to be study or site specific. This is not really surprising given the inherent complexity of the natural world and the continuously changing nature of the environment, with weather patterns, atmospheric layers, surface interactions, biogeographic distribution and temporal change all contributing to the challenge. For the Polar regions, overall complexity and environmental heterogeneity remain the greatest challenge in aerobiology having resolved detection limits, sample resolution and remote access issues. Hence, it is probably not surprising that where we look also tends to dictate what we find. Indeed, through work in both Polar regions, we have found that while there is both high heterogeneity and variability, there also might be patterns and an underlying core microbiome. However, one way to unlock this complexity further might be to focus on functional rather than taxonomic markers. In attempting such a transition, we found the underlying patterns were very different. With one eye on the forthcoming IPY in 2032-33, it might be worth considering a shift of emphasis towards specific functional marker genes and maybe develop a coordinated effort to look at a suite of such genes that could be important in the structure of the atmospheric microbiome and in atmospheric function.
How to cite: Pearce, D.: The Atmospheric Microbiome – untangling complexity in the Polar regions, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8028, https://doi.org/10.5194/egusphere-egu26-8028, 2026.
Valley fever is a lung infection caused by the inhalation of infectious spores from the fungi Coccidioides spp., a genus of soil dwelling fungal pathogen endemic to the arid regions of the southwestern United States, Mexico, Central and South America. Valley fever can exclusively be acquired through environmental reservoirs and is non-communicable from host to host. Very few Valley fever studies have focused on detecting Coccidioides spores in airborne respirable particles, which is the vector to infection. This study looks at the presence of Coccidioides in the air, soil, and burrow systems at a highly positive site in Mesa, Arizona. Monthly soil samples were taken from 14 animal burrows and 2 – 40 meter transects. Aerosol samples were collected for 24 hours every 6 days, following the Environmental Protection Agency sampling schedule. Two types of filter media were used for aerosol sampling: quartz fiber filters were used to determine gravimetric PM10, key ions, and organic and elemental carbon, and cellulose filters were used to analyze key elements. Meteorological data, including relative humidity, wind speeds, wind direction, and temperature were collected from a nearby weather station. Temporal soil sampling showed that C. posadasii stayed present at the site during the entire duration of the study however, temporal fluctuations of fungal burden occurred with decreases in detection occurring in the early spring and mid-summer months. Spatial variation was also detected, with certain burrow systems maintaining a high fungal burden throughout the year while others transiently housing the pathogen. We also showed that the pathogen was detected in rodent burrows significantly more frequency than in our surface soil transects. The temporal patterns of positivity for all the burrows were consistent over three years of sampling. Coccidioides were detected in ~68% of aerosol samples. Bulk PM10 did not have a statistically significant relationship with presence of Coccidioides, however, there was a statistically significant relationship between the amount of crustal material in the aerosols and presence of Coccidioides. Crustal material was reconstructed using the primary elements that make up earth’s crust (Al, Si, Fe, Ca, and Ti). Previous studies often link the presence of Coccidioides in the air with bulk PM10 concentrations; however, we found that looking at bulk PM10 concentrations gives an incomplete story. Additionally, there were statistically significant relationships with presence of Coccidioides and meteorological parameters, such as relative humidity and wind speed. This study emphasizes the importance of dust entrainment in the aerosolization and transport of Coccidioides.
How to cite: Stout, A., Ramsey, M. L., Kollath, D. R., Barker, B. M., Herckes, P., and Fraser, M.: Temporal surveillance of Coccidioides in soils and aerosols at a single location in Arizona, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8047, https://doi.org/10.5194/egusphere-egu26-8047, 2026.
Airborne aerosols impact urban air quality and public health through transport and inhalation of chemical pollutants and microbial agents, including antibiotic-resistant bacteria. However, relationships between particle size, environmental parameters, chemical and microbial composition, and antibiotic-resistance dispersion remain poorly understood. This study examined the interplay between these parameters for size-segregated airborne particles collected in a mid-sized urban area. Fine particles (<1.5 µm) contained elevated K⁺, NH₄⁺, Cl⁻, and anthropogenic carbonaceous compounds, with predominant Proteobacteria. Coarse fractions (>1.5 µm) mainly contained mineral-derived components (Mg²⁺, Ca²⁺) and carbonate carbon from natural sources, with greater microbial diversity dominated by Firmicutes (29%) and Actinobacteriota (25%). Key opportunistic pathogens (Acinetobacter, Staphylococcus, Lactobacillus) and antibiotic resistance genes with tetW and sul1 being the most abundant, followed by blaTEM and intl1 were significantly more abundant in coarse fractions. Particle size, rather than seasonality, was found to primarily determine chemical composition and microbial community structure. Key genera (Acinetobacter, Delftia, Paucibacter, Pseudomonas) positively correlated with anthropogenic chemicals but negatively with ARGs, while ARG-harboring genera associated strongly with mineral nutrients. These findings suggest coarse urban aerosols function as reservoirs of antibiotic resistance genes and opportunistic pathogens, with abundance peaking in warmer months, raising public health concerns through inhalation exposure.
How to cite: Habeebrahuman, H. B., Qian, Y., Shrivastava, V., Rafeeq, S., Dikmen, E., Sağırlı, E., Birgül, A., Karakuş, P., Oikonomou, K., Tsagkaraki, M., Sciare, J., Mihalopoulos, N., Öztürk*, F., and Lang-Yona*, N.: Particle Size Determines the Distribution of Chemical Composition and Antibiotic Resistance Genes in Urban Atmospheric Bioaerosols., EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8073, https://doi.org/10.5194/egusphere-egu26-8073, 2026.
The atmosphere could be one of Earth’s largest and most interconnected ecosystems. It is an environment characterized by low temperatures, low nutrient availability, aridity, and high ultraviolet radiation. Nevertheless, research in cold, arid and oligotrophic extreme environments have demonstrated that the conditions of the atmosphere are within the boundaries currently considered to support microbial life. Moreover, certain microorganisms are capable of gaining energy by oxidizing atmospheric gasses (hydrogen (H2), carbon monoxide (CO) and methane (CH4)) at trace concentrations. Measurement and experimental investigations of the atmospheric microbiome (the aeromicrobiome) are extremely challenging due to the compounding difficulties of low biomass samples, contamination issues, and lack of standardized sampling procedures. Numerical modelling can advance aeromicrobiology research by providing a complementary means to evaluate the habitability of the atmosphere and the potential activity of atmospheric microorganisms. We developed a theoretical framework combining the state-of-the-art knowledge of potential atmospheric-dwelling microorganisms, thermodynamic principles, and global climate and atmospheric gas composition data from MERRA2 (Modern-Era Retrospective analysis for Research and Applications, v2) and CAMS (Copernicus Atmosphere Monitoring Service). Our modelling analysis demonstrates that hydrogen oxidation, carbon monoxide oxidation, and methane oxidation are energy yielding catabolisms (ΔGr < 0, i.e. thermodynamically feasible) under atmospheric conditions, throughout the entire troposphere, all year round. It is therefore possible that these catabolisms are a viable source of energy to microorganisms in the atmosphere. We also reveal spatially and temporal energetic ‘hot spots’ where catabolic energy yield is greater, due to localized atmospheric gas concentrations and temperatures. In addition to supplying energy, atmospheric methane oxidation and hydrogen oxidation generate water as a catabolic byproduct, potentially alleviating limitations to microbial survival and activity that are imposed by the extreme aridity of the atmosphere. Theoretical modelling can accelerate aerobiology research by generating theory-informed hypotheses about which microbial cohorts are more probable to be metabolically active in the Earth’s atmosphere and guiding experimental research to where and how we may find and study them.
How to cite: Martinez-Rabert, E., Molares Moncayo, L., Nisa Kasapli, B., Trembath-Reichert, E., Lappan, R., Greening, C., Goordial, J., and A. Bradley, J.: Energetic constraints to the survival and activity of microbial life in Earth’s atmosphere, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8509, https://doi.org/10.5194/egusphere-egu26-8509, 2026.
Biological aerosol particles influence atmospheric processes, including cloud ice nucleation through action as ice-nucleating particles (INPs). Their abundance is altered by convective storm processes such as precipitation and cold pools. To improve the understanding of bioaerosol characteristics, sources, and variability during convective storms, we conducted two intensive field campaigns in May–June 2022 and 2023 at a semiarid grassland area in Colorado. The two seasons had contrasting environmental conditions, with exceptionally dry conditions in 2022 and unusually wet conditions in 2023. Bioaerosols were characterized using fluorescence and chemical tracers, while INPs were measured in air (before, during, and after rainfall), precipitation water, and terrestrial source samples; these measurements were aligned with disdrometer- and drone-based observations. Peak fluorescent particle concentrations correlated significantly with cold pool strength (rs=0.81, p<0.05, n=12), indicating that cold pools increase local bioaerosol concentration. Near-surface warm-temperature INP concentrations reached very high values during rainfall, with a maximum value across 15 events of 2.4 INP standard L-1 active at –10 °C. Much of the observed variability in during-precipitation concentration of INPs active between –8 °C and –25 °C was explained by cumulative rainfall kinetic energy (rs=0.71-0.91, p<0.006, n=14), suggesting that raindrops and hailstone impacts on land surfaces aerosolize bioaerosols and INPs. These rain-induced INPs were associated with particles <10 µm, based on size-segregated samples. Heat-treatment experiments (50 °C and 95 °C) revealed that INP properties in during-precipitation air were more similar to plants than to soil. Overall, the results indicate that rain-induced INPs are most likely dominated by fungi that reside on plant surfaces. Finally, cloud-resolving model simulations further suggest that a small fraction of rain-sourced tracers of bioaerosols reaches the upper levels of the parent storms, where INPs could influence cloud ice fraction and initiate precipitation, contributing to an aerosol-cloud-precipitation feedback.
How to cite: Mignani, C., Perkins, R. J., Feldman, T. K., Davis, C. M., Grant, L. D., van den Heever, S. C., Stone, E. A., DeMott, P. J., and Kreidenweis, S. M. and the BACS and BROADN team members as well as collaborators: Bioaerosol and ice-nucleating particle responses to convective storm processes at a semiarid grassland area in Colorado, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14699, https://doi.org/10.5194/egusphere-egu26-14699, 2026.
Atmospheric ice nucleating particles (INP) trigger ice formation in supercooled water, influencing cloud microphysics and precipitation. While mineral particles are abundant in the atmosphere, microbially produced compounds have been linked to INP with an ability to nucleate ice at temperatures >-10°C. Agricultural soils, which cover roughly 37% of Earth’s land surface, have been identified as reservoirs of these potent biological INP (bioINP). However, it remains unclear how site conditions and common agricultural practices, such as tillage, cover cropping, and liming, influence the abundance of bioINP and whether these effects are linked to changes in microbial community composition. To address this, we quantified INP concentrations and properties in soils from five Danish long-term agricultural field trials (LT sites) and characterized microbial communities using high-throughput sequencing of 16S rRNA and ITS marker genes. In addition, we established two aerosol sampling sites (AE sites) in agricultural areas in Denmark to monitor soil-derived bioaerosol emissions. We collected aerosol, soil, plant, and faecal samples at these two sites and used high-throughput 16S rRNA sequencing to quantify the fraction of bioaerosols derived from soils.
BioINP concentrations varied over several orders of magnitude between sites, with particularly high levels observed in Flakkebjerg, the most clay-rich of the five LT sites. Soil management practices influenced microbial community composition but had limited and inconsistent effects on bioINP abundance. Bacterial taxa previously reported as ice nucleation active, including Pseudomonas and Lysinibacillus, were detected only at low relative abundances and showed weak correlations with BioINP activity. In contrast, fungal community composition was a stronger predictor, with the relative abundance of Fusarium spp. and taxa like Linnemannia significantly associated with elevated BioINP concentrations. At the AE sites, we applied the source-tracking tool FEAST and found that 8% of the bioaerosols could be tracked to agricultural soils regardless of the season. This suggests that soil-derived particles are efficiently transferred into the atmosphere, even when soils are not directly exposed due to vegetation cover.
Our results suggest that fungi, particularly Fusarium, are the dominant contributors to warm-temperature bioINP activity in agricultural soils and that agricultural soils serve as an important source of airborne bioaerosol particles. This study, therefore, highlights the need to consider fungal ecology when linking agricultural management to atmospheric processes. Future work will quantify the absolute abundance of Fusarium using qPCR, determine fluxes of soil-derived BioINPs under different wind and rainfall conditions, and assess their impacts on cloud dynamics and climate.
How to cite: Šantl-Temkiv, T., Ellebæk, A., Langhoff, C. F., Løfstedt, E. M., Castenschiold, C. D. F., Greve, M. B., Sigsgaasd, T., Elsgaard, L., and Jensen, L. Z.: Biogenic ice nucleating particles in agricultural soils: Microbial drivers across different management practices and contribution to bioaerosol emissions, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-16337, https://doi.org/10.5194/egusphere-egu26-16337, 2026.
The Sea Surface Microlayer (SML) is a unique chemical and biological interface between the ocean and the atmosphere, playing a fundamental role in global biogeochemical cycles. Notably, the SML acts as the primary gateway for the emission of marine bacteria from the water column into the atmosphere and therefore serves as a critical interface between the ocean and the atmosphere. Despite its importance, direct biological sampling in the open sea remains technically challenging due to physical disturbances and the inherent fragility of the microlayer. To address these limitations, we developed and validated a dedicated biological sub-sampling methodology designed to facilitate SML collection and analysis in a controlled environment. The technique utilizes laboratory-based SML reformation from surface-water (SW) subsamples. To determine the optimal sampling window, 24-hour incubation experiments and 16S rRNA gene quantification were conducted using field samples and enriched marine bacteria. Results showed that while the SML exhibited compositional instability during the first two hours post-sampling, a consistent steady state in bacterial abundance was achieved between 3 and 6 hours. Consequently, a 4-hour stabilization period was established as the optimal timeframe for representative SML collection. Further results on the stability of the SML microbial composition will be discussed. The methodology was validated via comparative assessments against in situ sampling in the Mediterranean and Red Seas. Statistical analyses confirmed no significant differences in 16S rRNA gene copy numbers between field-collected and laboratory-reformed samples (p > 0.05). Application of this protocol across a Pacific Ocean latitude gradient revealed distinct microbial signatures in SW, the SML, and the atmosphere. Genomic data positioned the SML as a transitional mediator between the ocean and air, while 16S rRNA transcript analysis showed tight clustering in the SML and atmosphere, suggesting selective environmental control over active communities. Collectively, this stabilization approach provides a robust and standardized alternative to traditional sampling, particularly in rough sea conditions. By enabling stable biological characterization of the SML, this research enhances our understanding of the mechanisms controlling marine-atmosphere microbial exchange and their impact on global ecological networks and nutrient cycling.
How to cite: Argaman Meirovich, O., Tastassa, A. C., Dubowski, Y., Blaustein, J., and Lang-Yona, N.: Development a Laboratory Based Sub-Sampling Methodology for Sea Surface Microlayer Biological Characterization, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-16384, https://doi.org/10.5194/egusphere-egu26-16384, 2026.
Biogenic ice-nucleating particles (INPs) are widely detected in the Arctic atmosphere, where they potentially modulate Arctic mixed-phase clouds and consequently impact the regional climate. However, limited data on source environments, abundance, diversity, and atmospheric concentrations of biogenic INPs give rise to substantial uncertainties in aerosol-cloud interactions. As Arctic warming reduces snow and ice cover, accelerates greening, and increases periods of vegetation exposure, the aerosolization of plant-associated biogenic INPs may be enhanced. To better constrain the role of the phyllosphere microbiota and INPs in Arctic mixed-phase clouds, we collected quantitative data on INP and microbial community composition across three sites in western Greenland (Kangerlussuaq, Ilulissat, and Disko Island). Sampling was conducted from June to September, with each site visited two to three times. We combined freezing assays with bacterial community profiling and cultivation-based approaches. In addition, atmospheric samples were collected on filters (0.8 pore size) continuously from May to September on Disko Island to monitor variation in bioaerosol types and concentrations across the summer season. We further investigated phyllosphere-associated microbial communities and biogenic INPs. Highly active INPs were detected across all locations, with onset freezing temperatures ranging from -3°C to -7°C. The highest INP concentration per gram of plant material active at -10°C was observed in Kangerlussuaq in September, when temperatures drop to subzero degrees, suggesting that environmental factors, such as temperature, trigger INP production. Members of the genus Pseudomonas were consistently present in the plant samples, and cultivation studies yielded eight ice-nucleation active (INA) isolates, all affiliated with this genus. Whole genome sequencing revealed that the isolates represented novel species and contained genes that encode ice-nucleation active proteins (INpro). Our findings show that the Arctic phyllosphere can serve as a source of highly active biogenic INPs and thus may contribute to regional atmospheric INP levels and further impact cloud processes. We conclude that biogenic INPs derived from the Arctic phyllosphere need to be included in atmospheric models to improve predictions of Arctic climate feedback.
How to cite: Castenschiold, C. D. F., Lebert, S., Graversen, T. H., Kumari, S. P., Finster, K., and Šantl-Temkiv, T.: Highly Active Biogenic Ice-Nucleating Particles of the West Greenland Phyllosphere may Impact Arctic Weather and Climate, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-19882, https://doi.org/10.5194/egusphere-egu26-19882, 2026.
Biodegradation by airborne bacteria in clouds represents a potential sink for C1 and C2 monofunctional organic compounds in the atmosphere [1,2], yet this sink remains largely unaccounted for in atmospheric chemistry models. Several factors contribute to this gap: (i) Biodegradation rates are available for only a limited number of atmospheric bacteria strains and organic substrates, and (ii) systematic measurements of ambient bacteria concentration and diversity, which are needed for model initialization, are sparse.
To identify compounds for which biodegradation may represent an efficient sink in the atmosphere, we performed model sensitivity studies to identify key parameters that most significantly influence the biodegradation rates for organics in the atmospheric multiphase system, where biodegradation occurs in a small subset (0.1%) of cloud droplets. These parameters include bacterial cell concentration (Nbact) and diversity, and biodegradation rate constants (kbact), as well as the physicochemical properties of the biodegraded substrates, such as Henry’s law constants (KH) and chemical reactivity.
Our findings indicate that the amount of biodegraded material (ΔC) scales approximately with the number of active bacteria cells (ΔC ∝ Nbact). Sensitivity of ΔC to the Henry’s law constants of the organic substrate and to biodegradation rate constants are lower, with ΔC ∝ 0.9 KH and ΔC ∝ 0.4 kbact, respectively. However, we find that biodegradation is unlikely to be a significant sink for highly soluble and/or quickly biodegraded compounds that exceed KH ~ 105 M atm-1 and kbact ~ 2·10-13 L cell-1 s-1. For these compounds, biodegradation in individual cloud droplets proceeds so efficiently that the substrate replenishment from the gas phase is not sufficiently fast. Comparing biodegradation rate constants for major organics in cloud water to those derived from measurements in other aquatic environments, such as rivers [3], shows good agreement. Based on this, we suggest that a general rate constant (kbact = 2·10-13 L cell-1 s-1) can be used to estimate the loss of total water-soluble organic carbon in clouds.
In conclusion, our model sensitivity studies provide guidance for future lab and field measurements to constrain the data needed to assess the role of biodegradation as a sink for organics in the atmosphere. The identified sensitivities across wide parameter ranges will help to identify conditions and substrates for which atmospheric biodegradation may be significant.
[1] Nuñez López, L., Amato, P., and Ervens, B.: Bacteria in clouds biodegrade atmospheric formic and acetic acids, Atmos. Chem. Phys., 24, 5181–5198, https://doi.org/10.5194/acp-24-5181-2024, 2024.
[2] Khaled, A., Zhang, M., Amato, P., Delort, A.-M., and Ervens, B.: Biodegradation by bacteria in clouds: An underestimated sink for some organics in the atmospheric multiphase system, Atmos. Chem. Phys. 21, 3123–3141, https://doi.org/10.5194/acp-21-3123-2021, 2021.
[3] Catalán, N., J. P. Casas-Ruiz, D. von Schiller, L. Proia, B. Obrador, E. Zwirnmann and R. Marcé, Biodegradation kinetics of dissolved organic matter chromatographic fractions in an intermittent river, J. Geophys. Res. Biogeosci., 122, 131– 144, https://doi.org/10.1002/2016JG003512, 2017.
How to cite: Ervens, B., Nuñez López, L., and Amato, P.: Key Model Parameters for Constraining Biodegradation as an Atmospheric Sink for Organic Compounds, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-20342, https://doi.org/10.5194/egusphere-egu26-20342, 2026.
