scholarly journals A possible role of ground-based microorganisms on cloud formation in the atmosphere

2010 ◽  
Vol 7 (1) ◽  
pp. 387-394 ◽  
Author(s):  
S. Ekström ◽  
B. Nozière ◽  
M. Hultberg ◽  
T. Alsberg ◽  
J. Magnér ◽  
...  
Keyword(s):  
Surface Tension ◽  
Atmospheric Aerosols ◽  
Hydrological Cycle ◽  
Molecular Structures ◽  
Cloud Formation ◽  
Cloud Droplets ◽  
Natural Substances ◽  
Marine Site ◽  
Better Than

Abstract. The formation of clouds is an important process for the atmosphere, the hydrological cycle, and climate, but some aspects of it are not completely understood. In this work, we show that microorganisms might affect cloud formation without leaving the Earth's surface by releasing biological surfactants (or biosurfactants) in the environment, that make their way into atmospheric aerosols and could significantly enhance their activation into cloud droplets. In the first part of this work, the cloud-nucleating efficiency of standard biosurfactants was characterized and found to be better than that of any aerosol material studied so far, including inorganic salts. These results identify molecular structures that give organic compounds exceptional cloud-nucleating properties. In the second part, atmospheric aerosols were sampled at different locations: a temperate coastal site, a marine site, a temperate forest, and a tropical forest. Their surface tension was measured and found to be below 30 mN/m, the lowest reported for aerosols, to our knowledge. This very low surface tension was attributed to the presence of biosurfactants, the only natural substances able to reach to such low values. The presence of strong microbial surfactants in aerosols would be consistent with the organic fractions of exceptional cloud-nucleating efficiency recently found in aerosols, and with the correlations between algae bloom and cloud cover reported in the Southern Ocean. The results of this work also suggest that biosurfactants might be common in aerosols and thus of global relevance. If this is confirmed, a new role for microorganisms on the atmosphere and climate could be identified.

scholarly journals A possible role of ground-based microorganisms on cloud formation in the atmosphere

2009 ◽  
Vol 6 (5) ◽  
pp. 10035-10056 ◽  
Author(s):  
S. Ekström ◽  
B. Nozière ◽  
M. Hultberg ◽  
T. Alsberg ◽  
J. Magnér ◽  
...  
Keyword(s):  
Surface Tension ◽  
Atmospheric Aerosols ◽  
Hydrological Cycle ◽  
Molecular Structures ◽  
Cloud Formation ◽  
Cloud Droplets ◽  
Organic Fractions ◽  
Earth’S System ◽  
Better Than

Abstract. The formation of clouds is an important process for the atmosphere, the hydrological cycle, and climate, but also a difficult one to predict because some aspects of the transformations of aerosol particles into cloud droplets are still not well understood. In this work, we show that microorganisms might affect cloud formation without leaving the Earth's surface by releasing biological surfactants (or biosurfactants) in the environment, that make their way into atmospheric aerosols and should significantly enhance their conversion into of cloud droplets. In the first part of this work, the cloud-nucleating efficiency (or "CCN" efficiency) of standard biosurfactants was characterized by osmolality and surface tension measurements and found to be better than for any aerosol material studied so far, including inorganic salts. These results identify molecular structures that give to organic compounds exceptional CCN properties. In the second part, atmospheric aerosols sampled at different locations (temperate & tropical, forested & marine ones) were found to all have a surface tension below 30 mN/m, which can only be accounted for by the presence of biosurfactants. The results also showed that these biosurfactants were concentrated enough to significantly affect the surface tension of these aerosols and enhance their CCN efficiency. The presence of such strong biosurfactants in aerosols would be consistent with the recent identification of organic fractions of higher CCN efficiency than ammonium sulfate in aerosols. And a role of microorganisms at the Earth's surface on clouds could also explain previously reported correlations between algae bloom and cloud cover. Our results also suggest that biosurfactants might be common in aerosols and thus of global relevance. If their impact on cloud formation is confirmed by future studies, this work would have identified a new role of microorganisms at the Earth's surface on the atmosphere, and a new component of the Earth's system and climate.

scholarly journals In-cloud measurements highlight the role of aerosol hygroscopicity in cloud droplet formation

2016 ◽  
Author(s):  
Olli Väisänen ◽  
Antti Ruuskanen ◽  
Arttu Ylisirniö ◽  
Pasi Miettinen ◽  
Harri Portin ◽  
...  
Keyword(s):  
Cloud Droplet ◽  
Cloud Formation ◽  
Hygroscopic Growth ◽  
Cloud Droplets ◽  
Relative Contribution ◽  
Hygroscopic Particles ◽  
The Relationship ◽  
Aerosol Hygroscopicity

Abstract. The relationship between aerosol hygroscopicity and cloud droplet activation was studied at the Puijo measurement station in Kuopio, Finland, during the autumn 2014. The hygroscopic growth of 80, 120 and 150 nm particles was measured at 90 % relative humidity with a hygroscopic tandem differential mobility analyzer. Typically, the growth factor (GF) distributions appeared bimodal with clearly distinguishable peaks around 1.0‒1.1 and 1.4‒1.6. However, the relative contribution of the two modes appeared highly variable reflecting the varying presence of fresh anthropogenic particle emissions. The hygroscopicity-dependent activation properties were estimated in a case study comprising three separate cloud events with varying characteristics. At 120 and 150 nm, the activation efficiencies within the low- and high-GF modes varied between 0‒0.33 and 0.66‒0.86, respectively, indicating that the less hygroscopic particles remained almost non-activated, whereas the more hygroscopic mode was predominantly scavenged into cloud droplets. By modifying the measured GF distributions, it was estimated how the cloud droplet concentrations would change if all the particles belonged to the more hygroscopic group. According to the κ-Köhler simulations, the cloud droplet concentrations increased up to 70 % with increasing hygroscopicity. This is an indirect but clear illustration of the sensitivity of cloud formation to aerosol chemical composition.

scholarly journals Technical Note: The Role of Evolving Surface Tension in the Formation of Cloud Droplets

2018 ◽  
Author(s):  
James F. Davies ◽  
Andreas Zuend ◽  
Kevin R. Wilson
Keyword(s):  
Surface Tension ◽  
Pure Water ◽  
Cloud Droplet ◽  
Technical Note ◽  
Activation Mechanism ◽  
Activation Process ◽  
Cloud Droplets ◽  
Evolving Surface ◽  
Droplet Activation

Abstract. The role of surface tension (σ) in cloud droplet activation has long been ambiguous. Recent studies have reported observations attributed to the effects of an evolving surface tension in the activation process. However, adoption of a surface-mediated activation mechanism has been slow and many studies continue to neglect the composition-dependence of aerosol/droplet surface tension, using instead a value equal to the surface tension of pure water (σw). In this technical note, we clearly describe the fundamental role of surface tension in the activation of multicomponent aerosol particles into cloud droplets. It is demonstrated that the effects of surface tension in the activation process depend primarily on the evolution of surface tension with droplet size, typically varying in the range 0.5σw ≲ σ ≤ σw due to the partitioning of organic species with a high surface affinity. We go on to report some recent laboratory observations that exhibit behavior that may be associated with surface tension effects, and propose a measurement coordinate that will allow surface tension effects to be better identified using standard atmospheric measurement techniques. However, interpreting observations using theory based on surface film and liquid-liquid phase separation models remains a challenge. Our findings highlight the need for experimental measurements that better reveal the role of composition-dependent surface tensions, critical for advancing predictive theories and parameterizations of cloud droplet activation.

scholarly journals Heterogeneous nucleation of water vapor on different types of black carbon particles

2020 ◽  
Author(s):  
Ari Laaksonen ◽  
Jussi Malila ◽  
Athanasios Nenes
Keyword(s):  
Water Vapor ◽  
Black Carbon ◽  
Heterogeneous Nucleation ◽  
Hydrological Cycle ◽  
Quantitative Description ◽  
Nucleation Theory ◽  
Cloud Formation ◽  
Cloud Droplets ◽  
Carbon Particles ◽  
Different Types

Abstract. Heterogeneous nucleation of water vapor on insoluble particles affects cloud formation, precipitation, the hydrological cycle and climate. Despite its importance, heterogeneous nucleation remains a poorly understood phenomenon that relies heavily on empirical information for its quantitative description. Here, we examine heterogeneous nucleation of water vapor on and cloud drop activation of different types of soots, both pure black carbon particles, and black carbon particles mixed with secondary organic matter. We show that the recently developed adsorption nucleation theory quantitatively predicts the nucleation of water and droplet formation upon particles of the various soot types. A surprising consequence of this new understanding is that, with sufficient adsorption site density, soot particles can activate into cloud droplets – even when completely lacking any soluble material.

scholarly journals Technical note: The role of evolving surface tension in the formation of cloud droplets

2019 ◽  
Vol 19 (5) ◽  
pp. 2933-2946 ◽  
Author(s):  
James F. Davies ◽  
Andreas Zuend ◽  
Kevin R. Wilson
Keyword(s):  
Surface Tension ◽  
Pure Water ◽  
Cloud Droplet ◽  
Technical Note ◽  
Activation Mechanism ◽  
Activation Process ◽  
Cloud Droplets ◽  
Evolving Surface ◽  
Droplet Activation

Abstract. The role of surface tension (σ) in cloud droplet activation has long been ambiguous. Recent studies have reported observations attributed to the effects of an evolving surface tension in the activation process. However, the adoption of a surface-mediated activation mechanism has been slow and many studies continue to neglect the composition dependence of aerosol–droplet surface tension, using instead a value equal to the surface tension of pure water (σw). In this technical note, we clearly describe the fundamental role of surface tension in the activation of multicomponent aerosol particles into cloud droplets. It is demonstrated that the effects of surface tension in the activation process depend primarily on the evolution of surface tension with droplet size, typically varying in the range 0.5σw≲σ≤σw due to the partitioning of organic species with a high surface affinity. We go on to report some recent laboratory observations that exhibit behavior that may be associated with surface tension effects and propose a measurement coordinate that will allow surface tension effects to be better identified using standard atmospheric measurement techniques. Unfortunately, interpreting observations using theory based on surface film and liquid–liquid phase separation models remains a challenge. Our findings highlight the need for experimental measurements that better reveal the role of composition-dependent surface tensions, critical for advancing predictive theories and parameterizations of cloud droplet activation.

scholarly journals In-cloud formation of secondary species in iron-containing particles

2018 ◽  
Author(s):  
Qinhao Lin ◽  
Xinhui Bi ◽  
Guohua Zhang ◽  
Yuxiang Yang ◽  
Long Peng ◽  
...  
Keyword(s):  
Southern China ◽  
Cloud Formation ◽  
Dust Particles ◽  
Cloud Droplets ◽  
Aerosol Mass Spectrometer ◽  
Secondary Species ◽  
Cloud Processing ◽  
Aerosol Mass ◽  
Combustion Sources

Abstract. The increase of secondary species through cloud processing potentially increases aerosol iron (Fe) bioavailability. In this study, a ground-based counterflow virtual impactor coupled with a real-time single-particle aerosol mass spectrometer was used to characterize the formation of secondary species in Fe-containing cloud residues (dried cloud droplets) at a mountain site in southern China for nearly one month during the autumn of 2016. Fe-rich, Fe-dust, Fe-elemental carbon (Fe-EC), and Fe-vanadium (Fe-V) cloud residual types were obtained in this study. The Fe-rich particles, related to combustion sources, contributed 84 % to the Fe-containing cloud residues, and the Fe-dust particles represented 12 %. The remaining 4 % consisted of the Fe-EC and Fe-V particles. It was found that extremely high amounts of sulfate had already accumulated on the Fe-containing particles before cloud events, leading to no distinct changes in sulfate during cloud events. Cloud processing contributed to the enhancement of nitrate, chloride, and oxalate in the Fe-containing cloud residues. However, the in-cloud formation of nitrate and chloride in the Fe-rich type was less obvious relative to the Fe-dust type. The enhancement of oxalate in the Fe-rich cloud residues was produced via aqueous oxidation of oxalate precursors (e.g., glyoxylate). Moreover, Fe chemistry involved in the Fenton reaction further promoted the conversion of the oxalate precursors to oxalate during cloud events, although the photolysis of Fe-oxalate complexes also existed in the Fe-rich cloud residues. This work emphasizes the role of combustion Fe sources in participating in cloud processing and has important implications for evaluating Fe bioavailability from combustion sources during cloud processing.

scholarly journals Heterogeneous nucleation of water vapor on different types of black carbon particles

2020 ◽  
Vol 20 (21) ◽  
pp. 13579-13589
Author(s):  
Ari Laaksonen ◽  
Jussi Malila ◽  
Athanasios Nenes
Keyword(s):  
Water Vapor ◽  
Black Carbon ◽  
Heterogeneous Nucleation ◽  
Hydrological Cycle ◽  
Quantitative Description ◽  
Nucleation Theory ◽  
Cloud Formation ◽  
Cloud Droplets ◽  
Carbon Particles ◽  
Different Types

Abstract. The heterogeneous nucleation of water vapor on insoluble particles affects cloud formation, precipitation, the hydrological cycle, and climate. Despite its importance, heterogeneous nucleation remains a poorly understood phenomenon that relies heavily on empirical information for its quantitative description. Here, we examine the heterogeneous nucleation of water vapor on different types of soots as well as cloud drop activation of different types of soots, including both pure black carbon particles and black carbon particles mixed with secondary organic matter. We show that the recently developed adsorption nucleation theory quantitatively predicts the nucleation of water and droplet formation upon particles of the various soot types. A surprising consequence of this new understanding is that, with sufficient adsorption site density, soot particles can activate into cloud droplets – even when completely lacking any soluble material.

Simulation of the initial phase of Holuhraun eruption using the ICON-ART model to investigate aerosol- cloud interaction 

2021 ◽  
Author(s):  
Fatemeh Zarei ◽  
Corinna Hoose ◽  
Heike Vogel
Keyword(s):  
Hydrological Cycle ◽  
Number Concentration ◽  
Cloud Formation ◽  
Volcanic Plume ◽  
Source Strength ◽  
Cloud Droplets ◽  
Aerosol Cloud ◽  
Low Emission ◽  
High Emission ◽  
Aerosol Number Concentration

<p>Clouds play a key role in the atmosphere by completing the hydrological cycle and transferring water from the atmosphere to the earth's surface on the one hand, and affecting terrestrial radiation and solar radiation on the other hand. Although cloud properties are primarily affected by atmospheric dynamics, cloud microphysical features, which themselves are influenced by the number and chemical composition of aerosols that act as cloud condensation nuclei (CCN) and ice nuclei (IN) within cloud droplets, also affect cloud formation.</p><p> </p><p>The extent and quality of aerosols impact on cloud formation is one of the important open question of climate science. Volcanoes, which are a rich source of various chemical compounds, can help to improve the understanding of the effects of aerosols on clouds by providing a natural laboratory with locally high aerosol conditions adjacent to an unperturbed environment.</p><p> </p><p>In the present study, the impacts of changing the aerosol number concentration on clouds are investigated using the ICON-ART model. For this purpose, the Holuhraun volcano, which erupted on the island of Iceland in 2014, was simulated. It emitted small amounts of volcanic ash, and large emissions of gases primarily sulfur dioxide (SO2), which formed sulfate particles serving as CCN. Three simulations representing low, control, and high emission conditions were conducted. For the control simulation, the source strength of SO2 was based on the estimate by Malavelle et al. (2017). This rate, then, was reduced to one-fifth for the low emission experiment and increased by a factor of 5 for the high emission experiment.</p><p>First results indicate that increasing the source strength of SO2 is associated with an enhancement of sulfate aerosol number concentration and thus an increase of the number of cloud droplets, but with strongly nonlinear effects. For clouds within the volcanic plume, droplet concentrations are already high in the low emission scenario and do not increase significantly with higher emission strengths, partly due to model limitations. In addition, the effect of aerosols on the formation of cloud droplets is strongly dependent on environmental factors such as updraft velocity and supersaturation.</p><p>Keywords: Aerosol, Cloud, ICON-ART Model, Holuhraun eruption</p>

scholarly journals In-cloud measurements highlight the role of aerosol hygroscopicity in cloud droplet formation

2016 ◽  
Vol 16 (16) ◽  
pp. 10385-10398 ◽  
Author(s):  
Olli Väisänen ◽  
Antti Ruuskanen ◽  
Arttu Ylisirniö ◽  
Pasi Miettinen ◽  
Harri Portin ◽  
...  
Keyword(s):  
Cloud Droplet ◽  
Cloud Formation ◽  
Hygroscopic Growth ◽  
Cloud Droplets ◽  
Relative Contribution ◽  
Probable Presence ◽  
Hygroscopic Particles ◽  
Aerosol Hygroscopicity

Abstract. The relationship between aerosol hygroscopicity and cloud droplet activation was studied at the Puijo measurement station in Kuopio, Finland, during the autumn 2014. The hygroscopic growth of 80, 120 and 150  nm particles was measured at 90 % relative humidity with a hygroscopic tandem differential mobility analyzer. Typically, the growth factor (GF) distributions appeared bimodal with clearly distinguishable peaks around 1.0–1.1 and 1.4–1.6. However, the relative contribution of the two modes appeared highly variable reflecting the probable presence of fresh anthropogenic particle emissions. The hygroscopicity-dependent activation properties were estimated in a case study comprising four separate cloud events with varying characteristics. At 120 and 150 nm, the activation efficiencies within the low- and high-GF modes varied between 0–34 and 57–83 %, respectively, indicating that the less hygroscopic particles remained mostly non-activated, whereas the more hygroscopic mode was predominantly scavenged into cloud droplets. By modifying the measured GF distributions, it was estimated how the cloud droplet concentrations would change if all the particles belonged to the more hygroscopic group. According to κ-Köhler simulations, the cloud droplet concentrations increased up to 70 % when the possible feedback effects on effective peak supersaturation (between 0.16 and 0.29 %) were assumed negligible. This is an indirect but clear illustration of the sensitivity of cloud formation to aerosol chemical composition.

scholarly journals Impact of in-cloud aqueous processes on the chemical compositions and morphology of individual atmospheric aerosols

2020 ◽  
Author(s):  
Yuzhen Fu ◽  
Qinhao Lin ◽  
Guohua Zhang ◽  
Yuxiang Yang ◽  
Yiping Yang ◽  
...  
Keyword(s):  
Atmospheric Aerosols ◽  
Chemical Reactivity ◽  
Fractal Dimensions ◽  
Organic Coatings ◽  
Cloud Formation ◽  
Chemical Compositions ◽  
Microphysical Properties ◽  
Heterogeneous Chemical ◽  
Individual Particles

Abstract. The composition, morphology, and mixing structure of individual cloud residues (RES) and interstitial particles (INT) at a mountain-top site were investigated. Eight types of particles were identified, including sulfate-rich (S-rich), S-organic matter (OM), aged soot, aged mineral, aged fly ash, aged metal, fresh mixture, and aged mixture. A shift of dominant particle types from S-rich (29 %) and aged soot (27 %) in the INT to S-OM (24 %) and aged mixture (22 %) in the RES is observed. In particular, particles with organic shells are enriched in the RES (30 %) relative to the INT (12 %). Our results highlight the in-cloud formation of more oxidized organic shells on the activated particles. We also show that in-cloud processes may result in less compact soot, with the fractal dimensions (Df) of soot in the RES (1.82 ± 0.12) lower than those in the INT (2.11 ± 0.09). This research emphasizes the role of in-cloud processes on the chemistry and microphysical properties of individual particles. Given that organic coatings may determine the particle hygroscopicity, activation ability, and heterogeneous chemical reactivity, the increase of OM-shelled particles upon in-cloud processes should have considerable implications.

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