Kalliopi Violaki

Biological particles are an important but poorly understood component of Amazonian aerosols, having impacts on ecosystems, climate and human health. Here, we show that African dust plumes transport microbial communities across the Atlantic into the Amazon rainforest. We characterize the bacterial, fungal, and archaeal communities at 42 and 323 m above ground at the Amazon Tall Tower Observatory, both during background conditions and a five-day North African dust intrusion. Under background conditions, bacterial communities vary with height and time, reflecting diverse local and transported sources, whereas fungal communities remain stable and are dominated by locally produced fungi. During the dust intrusion, bacterial communities shift strongly towards microorganisms associated with dryland soils, biological soil crusts, and marine environments, while fungal communities remain unchanged. Additionally, airborne endotoxin concentrations increase threefold, without enriching obligate pathogens. Our findings demonstrate that African dust is not only a mineral nutrient source but also a vector of intercontinental microbial transport, with potential consequences for ecosystem functioning, atmospheric processes and human health.

Knowledge gaps in the source and parameterization of ice-nucleating particles (INPs) remain a major uncertainty in quantifying the properties and climate impacts of mixed-phase clouds (MPCs). Bioaerosols are increasingly recognized as important INPs for MPCs, yet it is unclear whether their contribution is critical through modelling studies. We investigate this using field observations at a semi-rural site in the central Europe, combining INP and aerosol measurements, remote sensing, and air-mass source analysis. We synergically use the results of in-situ and offline measurements to identify INPs originated from different sources, including biological aerosols, dust, and biomass burning aerosols, and to quantify their abundance and relative contributions to total INPs. More than 85% of immersion-mode INPs (>−24°C) are heat-labile and significantly correlated with fluorescent biological aerosols particles and pollen, while heat-resistant INPs (<~10%) are likely mineral dust, while biomass burning is an insignificant source. The proposed bioaerosol-ware INP parameterization reproduces observations across multi-regional datasets, showing that neglecting bioaerosol-INPs results in an average ~50% (~32%) bias in predictions of immersion-mode INPs active warmer than −15°C (−24°C), with frequent deviations of up to an order of magnitude from observations.

Knowledge gaps in the source and parameterization of ice-nucleating particles (INPs) remain a major uncertainty in quantifying the properties and climate impacts of mixed-phase clouds (MPCs). Bioaerosols are increasingly recognized as important INPs for MPCs, yet it is unclear whether their contribution is critical through modelling studies. We investigate this using field observations at a semi-rural site in the central Europe, combining INP and aerosol measurements, remote sensing, and air-mass source analysis. We synergically use the results of in-situ and offline measurements to identify INPs originated from different sources, including biological aerosols, dust, and biomass burning aerosols, and to quantify their abundance and relative contributions to total INPs. More than 85% of immersion-mode INPs (>−24°C) are heat-labile and significantly correlated with fluorescent biological aerosols particles and pollen, while heat-resistant INPs (<~10%) are likely mineral dust, while biomass burning is an insignificant source. The proposed bioaerosol-ware INP parameterization reproduces observations across multi-regional datasets, showing that neglecting bioaerosol-INPs results in an average ~50% (~32%) bias in predictions of immersion-mode INPs active warmer than −15°C (−24°C), with frequent deviations of up to an order of magnitude from observations.

Characterizing atmospheric bioaerosols is important for understanding their potential impacts on the environment and public health. In this study, we developed a novel flow cytometry-based approach to determine the low nucleic acid (LNA), high nucleic acid (HNA), dead, and intact bioaerosol populations in samples collected with a wet cyclone at Payerne, Switzerland, during spring and summer 2024. We found that the average bioaerosol number concentration reached (2.47 ± 3.35)×104 m−3. The HNA and intact populations were the most abundant populations, representing the largest fraction of total bioaerosols within 82% and 92% of the samples, respectively. Our results show that the LNA can be composed of dead bioaerosols, which correlated strongly with atmospheric particulate mass. Quantitative PCR and metagenomic analysis reveal significant correlations (Spearman, PERMANOVA, and Mantel) and associations between the different kingdoms analyzed, reflecting complex ecological interactions in the atmosphere among the communities. Despite this complexity, the LNA and HNA populations were mainly composed of bacteria, archaea, and fungi. Pollen abundance was positively correlated with temperature and negatively correlated with relative humidity (RH) and pollution (NOx and NO2), as these conditions promote the formation of sub-pollen particles (pollen fragments) through osmotic (bursting) and oxidative stress. Factor analysis indicates a seasonal dynamics transition from plant-associated bioaerosols in the spring season, to other bioaerosol types to be co-emitted during summer. Overall, the integration of flow cytometry with molecular analysis provides a framework to characterize and quantify bioaerosols and provides new insights into the ecological structure, variability, and sources of the atmospheric microbiome.

Knowledge gaps in the source and parameterization of ice-nucleating particles (INPs) remain a major uncertainty in quantifying the properties and climate impacts of mixed-phase clouds (MPCs). Bioaerosols are increasingly recognized as important INPs for MPCs, yet it is unclear whether their contribution is critical through modelling studies. We investigate this using field observations at a semi-rural site in the central Europe, combining INP and aerosol measurements, remote sensing, and air-mass source analysis. We synergically use the results of in-situ and offline measurements to identify INPs originated from different sources, including biological aerosols, dust, and biomass burning aerosols, and to quantify their abundance and relative contributions to total INPs. More than 85% of immersion-mode INPs (>−24°C) are heat-labile and significantly correlated with fluorescent biological aerosols particles and pollen, while heat-resistant INPs (<~10%) are likely mineral dust, while biomass burning is an insignificant source. The proposed bioaerosol-ware INP parameterization reproduces observations across multi-regional datasets, showing that neglecting bioaerosol-INPs results in an average ~50% (~32%) bias in predictions of immersion-mode INPs active warmer than −15°C (−24°C), with frequent deviations of up to an order of magnitude from observations.

Knowledge gaps in the source and parameterization of ice-nucleating particles (INPs) remain a major uncertainty in quantifying the properties and climate impacts of mixed-phase clouds (MPCs). Bioaerosols are increasingly recognized as important INPs for MPCs, yet it is unclear whether their contribution is critical through modelling studies. We investigate this using field observations at a semi-rural site in the central Europe, combining INP and aerosol measurements, remote sensing, and air-mass source analysis. We synergically use the results of in-situ and offline measurements to identify INPs originated from different sources, including biological aerosols, dust, and biomass burning aerosols, and to quantify their abundance and relative contributions to total INPs. More than 85% of immersion-mode INPs (>−24°C) are heat-labile and significantly correlated with fluorescent biological aerosols particles and pollen, while heat-resistant INPs (<~10%) are likely mineral dust, while biomass burning is an insignificant source. The proposed bioaerosol-ware INP parameterization reproduces observations across multi-regional datasets, showing that neglecting bioaerosol-INPs results in an average ~50% (~32%) bias in predictions of immersion-mode INPs active warmer than −15°C (−24°C), with frequent deviations of up to an order of magnitude from observations.

Greenlandic fjords are rapidly changing environments where ocean, ice, land, and atmosphere interact, yet aerosol sources and their role in cloud formation remain relatively unconstrained. To address this gap, we conducted an intensive field campaign in Narsaq, Southern Greenland, during summer 2023 as part of the GreenFjord project, combining ground-based sampling with a tethered balloon (24 flights to ∼700 m). Over six weeks, we measured meteorology, aerosol number size distributions, particle and CCN number concentrations, as well as optical properties. Aerosol characteristics varied markedly in time and altitude, reflecting four main sources: fresh anthropogenic pollution, aged background aerosols from local anthropogenic and marine origins, transported biomass burning, and new particle growth events. Local pollution dominated ∼50 % of the campaign, while growth events and Canadian wildfire plumes each contributed ∼8 %; the remainder (∼34 %) reflected aged marine background aerosols. Number size distributions were typically Aitken-mode dominated, presumably due to the frequently observed growth events. Biomass burning advection, in contrast, was marked by accumulation-mode particles. During plume periods, median CCN concentrations at 0.5 % supersaturation increased by a factor of 1.7–3.7 relative to median background concentrations, while median absorption and scattering coefficients increased by factors of 1.8–4.0 and 1.4–4.8, respectively. The enhancement factors are similar to or even exceed the enhancements from local anthropogenic pollution and highlight the substantial role that long-range transported biomass burning may have in modulating aerosol–cloud–radiation interactions over southern Greenland.

Greenlandic fjords are rapidly changing environments where ocean, ice, land, and atmosphere interact, yet aerosol sources and their role in cloud formation remain relatively unconstrained. To address this gap, we conducted an intensive field campaign in Narsaq, Southern Greenland, during summer 2023 as part of the GreenFjord project, combining ground-based sampling with a tethered balloon (24 flights to ~ 700 m). Over six weeks, we measured meteorology, aerosol size distributions, particle and CCN number concentrations, as well as optical properties. Aerosol characteristics varied markedly in time and altitude, reflecting four main sources: fresh anthropogenic pollution, aged background aerosols from local anthropogenic and marine origins, transported biomass burning, and new particle growth events. Local pollution dominated ~ 50 % of the campaign, while growth events and Canadian wildfire plumes each contributed ~ 8 %; the remainder (~ 34 %) reflected aged marine background aerosols. Number size distributions were typically Aitken-mode dominated, presumably due to the frequently observed growth events. Biomass burning advection, in contrast, was marked by accumulation-mode particles. During plume periods, median CCN concentrations at 0.5 % supersaturation increased by a factor of 1.7–3.7 relative to median background concentrations, while median absorption and scattering coefficients increased by factors of 1.8–4.0 and 1.4–4.8, respectively. The enhancement factors are similar to or even exceed the enhancements from local anthropogenic pollution and highlight the substantial role that long-range transported biomass burning may have in modulating aerosol–cloud–radiation interactions over southern Greenland.

Wet deposition is a major mechanism of phosphorus (P) deposition to the ultra-oligotrophic Eastern Mediterranean, yet long-term constraints on the relative roles of dissolved inorganic phosphorus (DIP) and dissolved organic phosphorus (DOP) remain limited. In this study, 15-year observations of DIP and DOP variability were conducted at an Eastern Mediterranean regional background site, focusing on the temporal variability, drivers, and deposition. Wet deposition samples were collected on an event basis and analyzed for DIP using a colorimetric molybdate-reactive method. Total dissolved phosphorus (TDP) was determined following oxidative digestion, and DOP was defined by subtracting DIP from TDP. Deposition fluxes were calculated by coupling concentration measurements with precipitation depth, enabling assessment of both concentration-driven and rainfall-driven variability.Across the 15-year period, both DIP and DOP exhibited pronounced event-to-event variability typical of atmospheric deposition in the region. Preliminary results show that DIP was frequently enhanced during dust outbreak episodes consistent with mineral dust influence, indicating efficient wet scavenging of particulate and soluble inorganic P associated with crustal minerals. In contrast, DOP was more frequently associated with air masses bearing marine and continental/anthropogenic impacts. At the interannual scale, variability in both concentrations and fluxes tracked changes in rainfall intensity and event frequency, as well as the occurrence of dust-transport episodes. To better constrain sources and processes, deposition chemistry was evaluated in tandem with air-mass back trajectories, and, where available, supporting aerosol and meteorological data. The results indicate that dust-driven wet deposition delivers episodic pulses of bioavailable DIP. DOP supplies a more sustained, compositionally diverse pool. This pool may become bioavailable following photochemical and microbial transformation after deposition. Overall, the 15-year record show that the organic fraction is significant and that the annual DIP:DOP partitioning can change depending on the transport pathways and rainfall distribution. This has direct implications for regional external nutrient inputs and their future projections in response to changes in dust emissions and hydroclimate. AcknowledgmentsThis work has been supported by the HFRI grant # 4050 BIOCAN.