Search Results (56)

The reduction in aviation-induced climate impacts requires not only decreasing CO₂ emissions, but also mitigating non-CO₂ effects such as persistent contrail cirrus. Alternative propulsion systems and fuels are therefore discussed as potential pathways toward climate-neutral aviation. However, their influence on contrail formation and evolution remains insufficiently understood, particularly regarding how emission characteristics translate into contrail microphysical behavior and lifetime. This study aims to bridge this knowledge gap by systematically evaluating the contrail-forming potential of Sustainable Aviation Fuel (SAF) and hydrogen-based propulsion systems, with a clear focus on identifying the key emission parameters that govern contrail persistence. To assess the impact of reduced particle emissions on contrail evolution, scenarios with lower initial ice crystal number concentrations $N_{\mathrm{ice}}$, representative of alternative propulsion concepts, were simulated using a Gaussian plume contrail evolution model. The results demonstrate that high ice crystal number concentrations ($N_{\mathrm{ice}}\approx {10}^{14}$–${10}^{15}$ kg⁻¹), characteristic of kerosene and many SAF combustion cases, lead to persistent contrails with lifetimes of approximately 9–12 h due to suppressed crystal growth and sedimentation. Conversely, low initial ice crystal concentrations ($N_{\mathrm{ice}}\approx {10}^9$–${10}^{10}$ kg⁻¹), expected for hydrogen systems under aerosol-limited nucleation conditions, promote short-lived contrails in the order of minutes. The findings indicate that contrail impacts are influenced not only by the fuel type itself, but also by combustion processes, atmospheric conditions, and the prevailing nucleation mechanisms. Consequently, the potential of SAF and hydrogen propulsion systems to mitigate contrail-related climate effects will likely depend on further technological optimization as well as additional experimental and in-flight observations to better quantify their atmospheric impacts. This work underscores the importance of linking emission measurements directly to contrail microphysics and provides a framework for evaluating future propulsion technologies based on their actual contrail-forming potential, rather than solely on fuel composition or CO₂ reduction. Full article

Persistent microplastics contaminate wastewater systems and pose significant environmental and human health risks due to their small size, buoyancy, persistence, and diverse physicochemical properties, which reduce the effectiveness of conventional treatment technologies. Freeze crystallization, indirect freeze crystallization, eutectic freeze crystallization, and ice-templated separation have emerged as promising long-term technologies for microplastic removal. Particle rejection at the solid–liquid interface, heterogeneous ice nucleation, brine channel formation, and particle entrapment within advancing ice fronts are key crystallization mechanisms governing microplastic separation. Microplastics can adhere to or nucleate growing ice crystals, according to lab and field research. These interactions influence crystal growth kinetics and ice structure formation. Indirect freeze crystallization (IFC) and related chemical-free crystallization systems offer lower energy requirements and improved scalability. Crystallization processes concentrate microplastics for downstream treatment, may connect with photochemical or oxidative degradation at ice interfaces, and are useful in cold areas or low-temperature industrial streams. Despite these advances, several challenges remain, including freezing rate, salinity, particle size distribution, and surface weathering, which are difficult to control. Integrating crystallization into wastewater treatment systems is also difficult. This review covers the latest advances in microplastic–ice interactions, crystallization engineering, and freeze-based separation technologies. It also highlights major knowledge gaps and suggests future research to use crystallization to remove microplastics from wastewater in a sustainable, scalable, and energy-efficient manner. Full article

Stratocumulus clouds are cloud systems composed of stratiform clouds with embedded convective clouds, possessing strong catalytic potential and serving as key target cloud systems for weather modification operations. In this study, the parameterization of ice nucleation for silver iodide (AgI) particles was applied to the Thompson microphysics scheme in the WRF model. Numerical experiments were designed for a stratocumulus cloud that occurred over the Hulunbuir region, northeastern China, on 31 May 2021, to investigate how the structure and evolution of cloud macro- and microphysical properties and precipitation formation respond to glaciogenic seeding. The simulation results indicate that AgI nucleation increased ice concentrations at 4–5 km altitude, enhancing ice crystal formation through condensation–freezing and deposition nucleation and the growth of ice particles through auto-conversion and riming, leading to increased precipitation. The results also show that owing to the non-uniform distribution of supercooled water within this stratocumulus cloud system, the consumption of AgI and the enhanced ice nucleation release latent heat more strongly in regions with higher supercooled water content. This leads to more pronounced isolated updrafts, altering the structure of shear lines and subsequently influencing regional precipitation distribution after silver iodide seeding concludes. These findings reveal that seeding influences both the microphysical and dynamic structures within clouds and highlight the non-uniform seeding effects within cloud systems. This study contributes to a deeper understanding of the effects of artificial seeding on stratocumulus clouds in high-latitude regions and holds significant reference value for artificial weather modification efforts in mixed-phase stratiform clouds. Full article

Black carbon (BC), as a potent light-absorbing aerosol, is mainly removed from the atmosphere through wet deposition. The efficiency of this process depends on the capacity of BC particles to serve as cloud condensation nuclei (CCN) or ice nuclei (IN). Newly emitted BC particles are typically small in size and highly hydrophobic, which limits their activation potential. However, atmospheric aging processes involving interactions with sulfates, nitrates, or organic matter enhance their hydrophilicity and nucleation capacity. Particle size serves as the critical link between aging and removal processes. Larger or coated BC particles are more readily activated and removed, while smaller particles require higher supersaturation levels. Both observations and models indicate that uncertainties in BC particle size distribution and aging processes lead to significant discrepancies in lifetime and transport estimates. This paper reviews recent research on the size dependence of wet removal of BC, evaluates current observational and modeling results, and proposes key research priorities to more accurately constrain its role in the climate system. Full article

Heterogeneous ice nucleation is a key process for ice cloud formation, snowfall, and freezing of water bodies. Ice nucleating particle (INP) cloud feedbacks are one of the largest sources of uncertainties in Earth’s Energy Budget. Although INPs are essential in the development of mixed-phased and glaciated clouds, their composition, sources, and cloud feedbacks remain poorly constrained. Previous studies have shown mixed results on the potential of light-absorbing particles (LAP), such as black carbon (BC) and high latitude dust (HLD), serving as INPs. However, many of these studies use laboratory or model-generated particles that may not represent the complex morphology and behaviors of ambient light-absorbing particles sufficiently. Here, we use in situ surface snow samples, collected during Spring 2018 in Svínafellsjökull, Iceland. The samples were analyzed by an immersion freezing mechanism for their ice nucleation activity (INA). Portions of the filtered samples were concentrated by lyophilization to observe the potential enhancement of INA. We investigated environmental samples of deposited aerosols to better understand the role activity of HLD and BC in ice nucleating activity in mixed-phase clouds in Iceland. We found concentrations of 16 ± 27 ng g⁻¹ and 33 ± 66 × 10⁶ ng g⁻¹ for BC and HLD, respectively. However, we found that isolated methanol-soluble organic aerosols have a more prominent role than BC and HLD in Iceland. We conclude that BC and HLD are insignificant INP but that they can inhibit INA from other INP. Full article

An analysis was conducted using AERONET Inversion Data at Thessaloniki and Leipzig stations. Aerosol type plays a vital role in determining their ability to act as CCN or INP, as properties such as chemical composition, morphology, and particle size influence their hygroscopic and ice-nucleating behavior. The CALIPSO mission provides global aerosol classification with vertical resolution by using backscatter intensity and depolarization ratio measurements. Aerosol typing from CALIPSO overpasses within 100 km of each selected AERONET station was used. Only pure aerosol cases (dust, polluted continental, smoke) were selected. This study combines AERONET-derived microphysical properties with CALIPSO aerosol classification to estimate particle number concentrations relevant for CCN and INP formation. The aim is to derive improved conversion factors for each aerosol type, enabling their application in future CCN and INP concentration profiles. Full article

The direct relationship between aerosols and clouds strongly influences the effects of clouds on the global climate. Aerosol particles act as cloud condensation nuclei (CCN) and ice nuclei (IN), affecting cloud formation, microphysics, and precipitation, as well as increasing the reflection of solar radiation at the cloud tops. Processes such as gas-to-particle conversion and new particle formation (NPF) control aerosol properties that, together with meteorological conditions, regulate cloud droplet nucleation through Köhler theory and related effects. The indirect aerosol effects described by Twomey and Albrecht demonstrate how changes in aerosols impact droplet number, cloud lifetime, and precipitation efficiency. Cloud microphysical processes, including droplet growth, collision-coalescence, and solid-phase mechanisms such as riming, vapor diffusion, and aggregation, shape precipitation development in warm, cold, and mixed-phase clouds. Ice nucleation remains a significant uncertainty due to the diversity of aerosol types and nucleation modes. This work synthesizes these physical interactions to better understand how the chemical and physical properties of aerosols influence cloud and precipitation processes, supporting improvements in weather and climate prediction models despite numerical challenges arising from the complexity of aerosol–cloud interactions. Full article

Cloud seeding is a weather modification technique for enhancing precipitation in arid and semi-arid regions, including the Western U.S. However, designing an optimal cloud seeding operation based on comprehensive evaluation metrics, such as seeding agent dispersion and atmospheric conditions, has yet to be thoroughly explored for this region. This study investigated the impacts of cloud seeding, particularly utilizing silver iodide, on ice particle growth within clouds through numerical modeling. By leveraging the Snow Growth Model for Rimed Snowfall (SGMR), the microphysical processes involved in cloud seeding across five distinct events were simulated. The events were in the Lake Tahoe region, nestled within the Sierra Nevada Mountain ranges in the Western U.S. This model was executed based on six primary variables, including cloud top height, cloud base height, cloud top temperature, cloud base temperature, liquid water content, and ice water content. This study incorporated datasets from the Modern-Era Retrospective Analysis for Research and Applications Version 2 and the Clouds and the Earth Radiant Energy System. The findings revealed the importance of ice nucleation, aggregation, diffusion, and riming processes and highlighted the effectiveness of cloud seeding in enhancing ice particle number concentration, ice water content, and snowfall rates. However, event-specific analyses indicated diverse precipitation responses to cloud seeding based on initial atmospheric conditions. The SGMR modeling hints at the importance of improving ice microphysical processes and provides insights for future cloud seeding research using regional and global climate models. Full article

Atmospheric ice nucleation particles (INPs) play a crucial role in influencing cloud formation and microphysical properties, which in turn impact precipitation and Earth’s radiation budget. However, the influence of anthropogenic activities on the properties and concentrations of INPs remains an area of significant uncertainty. This study investigated the physical and chemical characteristics of atmospheric ice nucleation particles in Huangshan, China during the May Day labor holiday period (spanning 8 days, from April 27th to May 5th). INP concentrations were measured at temperatures from −17 °C to −26 °C and relative humidities (RH_w) from 95% to 101%. Average INP concentrations reached 13.7 L⁻¹ at −26 °C and 101% RH, 137 times higher than at −17 °C and 95% RH. INP concentrations showed exponential increases with decreasing temperature and exponential increases with increasing RH. Concentration fluctuations were observed over time, with a peak of ~30 L⁻¹ (t = −26 °C, RHw = 101%) around the start and end of the holiday period. Aerosol number concentrations were monitored simultaneously. The peak in aerosols larger than 0.5 μm aligned with the peak in INP concentrations, suggesting a link between aerosol levels and INPs. Chemical composition analysis using SEM–EDX revealed the distinct elemental makeup of INPs based on the activation temperature. INPs active at warmer temperatures contained N, Na, and Cl, indicating possible biomass and sea salt origins, while those active at colder temperatures contained crustal elements like Al and Ca. Full article

Although studies focusing on the physicochemical properties of aerosols/clouds have not been performed extensively, even less attention has been given to hailstones and their biological composition. Here, we present the results of the physical and microbiological characterisation of 20 hailstones collected in Southern Brazil originating from two storms. Nearly half of the hailstones (9 out of 20, or 45%) did not contain any cultivable bacteria or fungi. A total of 18 bacterial species were found in hailstones from both storms, and the genus Bacillus was found in 5 out of the 11 hailstones, with Bacillus cereus being the most frequent bacterial species. Fungi, on the other hand, were only present in four hailstones derived from a single storm, with three fungal species identified and Epicoccum nigrum being the most frequent fungal species. HYSPLIT modelling indicated the different flow of air masses from the Amazon and Pacific Ocean that contributed to the loading of microorganisms found in the clouds at the time of the two storms. Our findings suggest that ca. 50% of hailstones have cultivable bacterial or fungal species, which came mainly from the local landscape with intrusions of air masses derived from the Amazon and the Pacific Ocean. Full article

Secondary ice productions (SIPs) can produce ice crystals with a number concentration much higher than that of ice nucleating particles in mixed-phase clouds and therefore influence cloud glaciation and precipitation. For midlatitude continental mesoscale convective systems (MCSs), how SIPs affect the microphysical properties and precipitation is still not clear. There are few studies of SIPs in midlatitude continental MCSs. This study investigates the roles of three SIPs (rime splintering, freezing drop shattering, and ice-ice collisional breakup) on a squall line case in North China on 18 August 2020 using the WRF model with a modified Morrison double-moment bulk microphysical scheme. Including SIPs, especially ice-ice collisional breakup, in the model simulations markedly improves the simulated convective area and convective precipitation rate of the squall line, while slightly improving the area and precipitation of the stratiform region. Within the mixed-phase layer in both the convective and stratiform regions of the squall line, ice-ice collisional breakup is the dominant process to generate ice crystals. In contrast, rime splintering generates an order of magnitude fewer ice crystals than ice-ice collisional breakup, while freezing drop shattering plays a negligible role due to the lack of large drops. Ice multiplication through ice-ice collisional breakup and rime splintering produces numerous snowflakes and graupel. This leads to enhanced depositional growth and weaker riming, which in turn weakens rime splintering. It is recommended to add SIP parameterization to the model. Full article

Ice-nucleating particles (INPs) are crucial for cloud freezing processes in the atmosphere. Given the limited knowledge about the vertical distribution of INPs and its relation to aerosols in China, we present two aircraft observations of INPs over the North China Plain on 23 October 2019 and 25 October 2019, before and after a cold front passage. We used a well-established method to identify the INPs on a silicon wafer and then performed single-particle chemical composition analysis using an environmental scanning electron microscope-energy dispersive spectrometer (ESEM-EDS). The INP concentrations range from 0.1 to 9.2 L⁻¹ within activation temperatures from −20 to −29 °C. INPs are mostly concentrated within the boundary layer, and their concentration shows a decreasing trend with height (0.5~6 km) before the cold front passage. However, the highest INP concentration always appears at higher altitudes (4~5 km) after the cold front passage. The cold front passage also significantly weakens the correlations between the concentrations of INPs and aerosol particles at different sizes. The activated fraction (AF) of total aerosols increases from 10⁻⁶ to 10⁻⁴ with height from near ground to 6 km, reflecting a better nucleating capacity of the aerosols at higher altitudes. There is no obvious variation in AF after the cold front passage. Chemical analysis reveals that the INPs containing mineral dust components comprise the majority of total INPs during both flights. The proportion of pure mineral dust declines from 52.2% to 43.5% after the cold front passage while the proportion of mixed mineral dust increases from 23.9% to 45.7%, suggesting that an increased probability of aging or coating of INPs is introduced by the cold front during their long-distance transport. In addition, 88% of INPs have a diameter larger than 1 μm. This indicates that larger aerosols (>1 μm) are the major contributors to INPs at high altitudes despite their relatively low abundance. Our results demonstrate a significant impact of transport events on the sources and vertical distribution of INPs in the atmosphere. Full article

The remote sensing ground-based platform for atmospheric research hosted by the ERATOSTHENES Centre of Excellence will be the key research infrastructure of the Cyprus Atmospheric Remote Sensing Observatory (CARO) in Limassol, Cyprus. Between the 27th of October to the 1st of November 2020, the lidar system observed a pronounced and well-aged stratospheric aerosol layer with a backscatter maximum around 10 km asl and clear wildfire smoke signatures. The observed smoke plume was caused by extreme wildfires on the west coast of the U.S. Long-range aerosol transport events observed over Limassol are used for the study of the influence of organic aerosol particles (serving as ice-nucleating particles, INPs) in a cirrus formation in the upper troposphere. Full article

Frazil ice comprises millimeter-sized ice crystal particles or flocculations in water, and its generation and evolution primarily occur during the initial stage of the river ice process. Meanwhile, ice damage caused by frazil ice is common, so it is crucial to determine its generation and evolution mechanisms to develop a full understanding of the river ice processes, the prediction of ice development, and ice damage prevention. The recent developments in frazil ice research and modeling are summarized in this article. From the perspectives of field measurements and laboratory experiments, the techniques and methods for observing frazil ice are reviewed, including the flow generation, temperature control, and observation techniques necessary for laboratory observations of frazil ice, as well as the challenging observation techniques used for field measurements. Frazil ice’s evolution mechanisms (nucleation, thermal growth, secondary nucleation, collisional fragmentation, and flocculation) are affected by water temperature processes. Work on the movement and distribution of frazil ice is also presented. A review of the current numerical models used to assess frazil ice evolution is conducted. Moreover, the open issues and potential future research topics are suggested. Full article

Aluminum alloy 6201 is a wrought, heat-treatable alloy, which is used in electricity transmission and distribution lines. The alloy is processed in a commercial continuous casting and rolling system, which includes a series of in-line thermomechanical processes involving hot working, quenching, cold working and artificial aging. In this study and following cold working, the alloy is subjected to a solution heat treatment at 510 °C for an hour, quenched in ice water, and artificially aged at various temperatures for various times (150–200 °C for 2–30 h) (T6-temper) in order to investigate the effect of precipitation on mechanical properties and electrical conductivity. The results show that optimum mechanical properties and electrical conductivity were obtained after artificial aging at 155 °C for 30 h (155-30). The tensile strength was almost equal to that of the as received cold drawn wire of 326 MPa, but interestingly, electrical conductivity significantly increased to 58.6% IACS from a value of 52.7% IACS of the as received cold drawn wire. Intermetallic particles α-AlFeSi (Al₈Fe₂Si) and β-AlFeSi (Al₅FeSi and Al₉Fe₂Si₂) were observed in all samples, which were nucleated during solidification and homogenization; they were not affected by the aging process. β″/β′/β -precipitates formed during artificial aging, which affected the final mechanical properties and the final electrical conductivity. Full article