Continuous Fog Research Articles

A new Janus mesh membrane with ultrafast directional water transportation and improved fog collection

Fog collection materials have been intensively investigated and can potentially be used to alleviate freshwater shortages. However, developing highly efficient fog collection materials remains challenging. Requisite improvements in fog collection technology are the ultrafast transportation of captured water and the effective regeneration of fresh regions on the surfaces of fog collection materials. Herein, a novel Janus mesh membrane (JMM) with an alternating hydrophobic–superhydrophilic-patterned hydrophobic surface and asymmetric wettability interface is prepared by a selective liquid-phase surface oxidation strategy. The unique structure and high-contrast wettability of the JMM enable ultrafast directional transportation of tiny water droplets (< 0.1 µL), thereby achieving an excellent water collection efficiency of 15.28 g h−1 cm−2, which is much higher than those of conventional Janus membranes. The JMM functioned as a versatile fog collector and maintained continuous fog collection regardless of the fog flow direction. This study offers a novel approach for preparing innovative fog collection materials and establishes a foundation for developing advanced fog collection systems suitable for diverse applications.

Durable Superhydrophobic Surfaces with Self-Generated Wenzel Sites for Efficient Fog Collection.

Harvesting freshwater from fog is one of the possible solutions to the global water scarcity crisis. Surfaces with both hydrophobic and hydrophilic regions are extensively employed for this purpose. Nevertheless, the longevity of these surfaces is still constrained by their delicate surface structures. The hydrophilic zones may become damaged or contaminated after repeated use, thereby compromising their effectiveness in fog collection. The preparation of generally applicable durable superhydrophobic coatings with self-generated Wenzel sites is reported here for long-term efficient and stable fog collection. The coatings are prepared by depositing the poly(tannic acid) coating as the primer layer on various substrates, self-assembly of trichlorovinylsilane into staggered silicone nanofilaments, and then thiol-ene click reaction with 1H,1H,2H,2H-perfluorodecanethiol. The coatings demonstrate remarkable static superhydrophobicity, robust impalement resistance, and stable self-generated Wenzel sites for water droplets. Therefore, the fog collection rate (FCR)of the coatings reaches 2.13g cm-2 h-1 during 192h continuous fog collection, which is triple that of bare substrate and outperforms most previous studies. Moreover, the systematic experiments and models have revealed that the key factors for achieving high FCR on superhydrophobic coatings are forming condensed droplets ≈1mm in critical radius and a Wenzel site proportion of 0.3-0.4.

Fog scavenging of particulate matters in air pollution events: Observation and simulation in the Yangtze River Delta, China

Stable atmospheric boundary layer is conducive to the accumulation of atmospheric pollution and the occurrence of fog, and fog has a removal effect on air pollution. In this study, we use the observation and WRF-Chem (Weather Research and Forecasting Model with Chemistry) simulation to analyze the factors affecting the removal efficiency in a continuous fog and haze episode from November 26 to 28, 2018 in Jiangsu Province, such as fog thickness and duration. The results show that the WRF-Chem simulation well reproduces the boundary layer characteristics in the stages of fog formation, development and dissipation. The atmospheric boundary layer provides favorable conditions for the maintenance of fog and air pollution. The inversion layer, with the maximum intensity of 3 °C per 100 m, creates favorable thermal conditions, and the water vapor advection is also conducive to the fog maintenance. The ground observation verifies the wet scavenging of PM2.5 during dense fog events. The scavenging effect is related to the fog duration, and the correlation is positive when the fog is just formed and negative when the fog is dissipating. The PM2.5 concentration decreases from 159 μg m−3 to 38 μg m−3 after the fog lasts for 11 h. The fog has a remarkable scavenging effect on PM2.5 in the vertical direction, due to the deposition effect of fog droplets on the pollutant particles. The PM2.5 concentration on the ground is lower than the vertical average in the fog area, and the scavenging effects during the dense fog periods on November 27 and 28 are 47.7 μg m−3 and 36.1 μg m−3, respectively. The fog duration is mostly concentrated in 3–17 h. When the duration of fog is 4–8 h, the scavenging effect on PM2.5 reaches the strongest, with an average PM2.5 concentration decrease of >70 μg m−3.

Bio‐inspired Copper Kirigami Motifs Leading to a 2D–3D Switchable Structure for Programmable Fog Harvesting and Water Retention

AbstractBio‐inspired fog harvesting devices (FHDs) have been exploited to address water shortages. Despite the advances achieved, efficient and continuous fog harvesting is still hindered by some challenges: 1) a single mechanism appears to be insufficient to achieve optimal water collection efficiency; 2) the re‐evaporation of the harvested water results in decreased water collection. In this study, inspired by the unique feature of cacti, Nepenthes alata, lotus leaves, and pinecones, a 2D–3D switchable copper sheet (SLP‐SHL@SP‐Cu) is reported, which results in excellent fog capture and water transport rates. During the fog harvesting process, the captured droplets transport from the tip of the top surface to the bottom under the Laplace forces (cacti spine), capillary forces (lotus leaves), and low surface energy (Nepenthes alata). Notably, the novel FHD responds in a preprogrammed manner to changes in humidity and performs a dynamic transformation from a 2D planar structure to a 3D helical structure (and in reverse), enabling efficient fog harvesting (in the 3D geometry) and water storage (in its 2D form). Thus, this study opens a new avenue for the practical applications of highly effective FHDs with increased water retention abilities.

Cactus-Inspired Janus Membrane with a Conical Array of Wettability Gradient for Efficient Fog Collection.

Fog collection plays an important role in alleviating the global water shortage. Despite great progress in creating bionic surfaces to collect fog, water droplets still could adhere to the microscale hydrophilic region and reach the thermodynamic stable state before falling, which delays the transport of water and hinders the continuous fog collection. Inspired by lotus leaves and cactuses, we designed a Janus membrane that functions to both collect fog from the air and transport it to a certain region. The Janus membrane with opposite wettability contains conical microcolumns with a wettability gradient and hydrophilic copper mesh surface. The apexes of conical microcolumns are superhydrophobic and the rest are hydrophobic. The fog droplets were deposited, coalesced, and directionally transported to the bottom of the conical microcolumns. Then, the droplets unidirectionally passed through the membrane and flowed into the water film on the surface of the copper mesh. The asymmetric structural and wettability merits endow the Janus membrane with an improved fog collection of ∼7.05 g/cm2/h. The study is valuable for designing and developing fluid control equipment in fog collection, liquid manipulation, and microfluidics.

A new species of wood-wren (Troglodytidae: Henicorhina) from the Western Andes of Colombia

A new species of Henicorhina wood-wren (Aves, Troglodytidae) is described from the Munchique massif of the Western Andes of Colombia. The Munchique Wood-Wren Henicorhina negreti is closely related to and probably derived from the Gray-breasted Wood-Wren Henicorhina leucophrys of Central and South America. Henicorhina negreti appears restricted to a narrow band of extremely wet, stunted cloud forest on the upper Pacific slope, characterized by nearly continuous fog, high epiphyte loads and frequent landslides; it is abruptly replaced in taller forest at lower elevations on this slope by H. l. brunneiceps, and on the drier east slope by H.l. leucophrys. The new species differs from adjacent forms of H. leucophrys in its distinctly barred abdomen, dark juvenal plumage, relatively short tail and longer tarsi. Its song is also very distinct, and the adjacent forms of H. leucophrys do not respond to it while they do to each others (despite the fact that the new species occurs between them). Conversely, the new species does not respond to songs of H. l. leucophrys or H. l. brunneiceps, strongly suggesting that it is reproductively isolated from them and has distinct habitat requirements. Similarities between the ecology of H. negreti and that of H. leucoptera, another restricted-range endemic sympatric but not syntopic with H. leucophrys, are discussed. Possible threats to H. negreti due to forest clearance and global climate change are discussed, and we suggest that the species be accorded Critically Endangered status.

Room Decontamination Using Ionized Hydrogen Peroxide Fog and Mist Reduces Hatching Rates of Syphacia obvelata Ova.

This study evaluated the efficacy of ionized hydrogen peroxide (iHP) fog and mist for environmental and surface decontamination of Syphacia obvelata ova in rodent rooms. Ova were collected by perianal tape impression from S. obvelata infected mice. In experiment 1, ova were exposed to iHP using a whole-room fogging decontamination system with a 15 min initial fog application cycle in unoccupied rodent rooms. Ova were removed from the fogged environment after a 15 min, 30 min, 90 min, or 240 min iHP exposure time. In experiment 2, a second cohort of ova were exposed to iHP using the whole-room fogging decontamination system. Ova were removed after 3, 4 or 6 continuous fog application cycles with 45 min dwelling time between each cycle and 15 h dwelling time for the last time point. In experiment 3, a third set of ova was exposed to an iHP surface misting unit with 1, 2, or 3 iHP mist applications. A 7 min contact time followed each application. After exposure, ova were incubated in a hatching medium for 6 h. Control ova were maintained at room temperature without iHP exposure before incubation in the hatching medium. After incubation, the number of ova hatched was assessed by microscopic examination. For experiment 1, results ranged from 46% to 57% of exposed ova hatched. For experiment 2, results ranged from 43% to 49% of ova hatched. For experiment 3, 37% to 46% of exposed ova hatched. Conversely, for the control groups above 80% of ova hatched for all 3 experiments. These data suggest that exposure to iHP fog and mist has variable effectiveness in reducing viability of S. obvelata ova at the time points tracked. Further studies are needed to identify iHP exposures that will further reduce or eliminate the hatching of rodent pinworm ova.

MODIS-Derived Arctic Melt Season Fog and Low Stratus over East Greenland Glaciers and the Ice Sheet

In a first attempt to quantify fog over vast snow and ice surfaces, we present the horizontal and vertical spatial extent of significant melt-season fog events over East Greenland glaciers and the Greenland ice sheet. Two established MODIS fog classification methods are adjusted for use in Arctic glacierized regions and applied to Terra-MODIS Collection 6 Level 1B scenes and Level 2 cloud products. In a 6-step procedure, we process these products in combination with a digital elevation model and glacier extents to separate fog from low stratus over glaciers. The procedure was optimized using Landsat 7 and ground observations and verified with concurrent CloudSat–CALIPSO very low-level clouds. The MODIS-derived end products are 500-m resolution fog and low stratus mask maps over East Greenland with associated fog statistics. Six days throughout the 2002–2007 melt season are mapped, revealing maximum fog extent in July–August covering 20,000–70,000 km2 of glacier surface. Mean fog thickness is ∼200 m and maximum inland extent of continuous fog ∼100 km, although patches occur high on the ice sheet. Our method and results will aid in cloud change detection and in the quantification of cloud radiative forcing and thermal effects over snow and ice surfaces.

Detection of Fog Using Temporally Consistent Algorithm With INSAT-3D Imager Data Over India

A fog detection algorithm using INSAT-3D imager data has been developed and tested. The algorithm emphasizes continuous fog detection as the current fog detection algorithm which is used for the operational fog product generation over India is having temporal discontinuity during dawn and dusk. Moreover, currently, the INSAT-3D fog product over India is being generated with different algorithms for day and night. In this paper, a single algorithm using brightness temperature difference of 3.9 and 10.8 μm wavelength for both day and night has been used. The thermal infrared, water vapor, and visible channel spectral information (for daytime) has been used as additional criteria to reduce false alarm. The thresholds used are determined dynamically using an image-based method. The spatial homogeneity test, which is a special characteristic of fog, has also been carried out to minimize false detection. Validation was carried out against visibility data over five airports in the Indo-Gangetic (IG) plains of India. It shows that probability of detection and false detection to be 66% and 10%, respectively, for 2013–2014 and 68% and 10% for 2015–2016. The algorithm is able to capture the entire life cycle of fog from formation to dissipation, consistently for both the season with different weather conditions.

Accelerated Corrosion Degradation of Coated Aluminum Alloy Systems through Galvanic Interactions

The use of structural aluminum alloys for aircraft is common due to its low density and relatively high strength. While exhibiting significant general corrosion resistance, these alloys are susceptible to various forms of localized corrosion, such as pitting, intergranular corrosion, etc. When in galvanic contact with fasteners noble to the aluminum alloy panel, these phenomena can be much more aggressive. In an effort to mitigate these problems, multi-layer coating systems are utilized to protect the aluminum alloy from aggressive environments and to prevent galvanic contact with dissimilar metals. However, defects in these coatings may lead to galvanic interaction with the fastener and localized attack of the underlying panel. In addition, delamination of coating at these sites can result in accelerated attack as the environment becomes more aggressive in these shielded areas. Previous work for this project has focused on the galvanic interaction of aluminum alloy 7075-T6 panels with stainless steel 316 fasteners when coated with either a chromated (chromate conversion coating, chromate-rich primer) or non-chromated (adhesion promoting pretreatment, praseodymium-rich primer) system in two environments: immersion in five weight percent sodium chloride and a continuous fog salt spray chamber. A test panel configuration using a scribed Al alloy panel and isolated fasteners was used. Galvanic current data can be acquired during exposure to determine total charge passed due to galvanic interaction between the fastener and panel for the purpose of approximating the extent of aluminum dissolution and comparison of the two coating systems. Post-exposure optical profilometry has been conducted on samples to gain insight on morphology of the attack, as well as to quantify the corroded volume of material. Analyses of this galvanic current data and morphology have been coupled to survey what coating strategy could be more beneficial. Current work focuses on identifying the susceptibility of certain areas of the test panel to localized attack and development of a damage function for galvanic corrosion degradation in coated aluminum alloy systems. Coating performance can be compromised at the fastener hole due to mechanical damage from the fastener and from inadequate coating coverage. Electrochemical impedance spectroscopy (EIS) has been utilized to determine the extent of coating protection at the fastener hole and assess the effects of defects that may serve as initiation sites for accelerated attack. Various fastener hole conditions have been compared to the protection afforded by the coating in areas away from the fastener hole. Impressed current has also been used to determine the feasibility of attack initiating when the unintentional coating defects within the fastener hole are not a factor. This process involves current being passed from a counter electrode to a panel without fasteners in solution, allowing control of the amount of charge passed, as well as the rate at which it is passed. With the absence of fasteners, current may be passed to any defect, regardless of proximity to the fastener hole. This technique of supplying current via a potentiostat can also be used in conjunction with a controlled, artificial defect (scribe) as a means to compare various coating systems. Contrary to the aforementioned technique, during this galvanostatic stressing, a fastener is used as the counter electrode and the exposure is carried out in a salt spray chamber, not in bulk solution. This allows for analysis of the coating systems under wetting and drying cycles that more closely resemble in-service conditions, while utilizing impressed current to better control and accelerate the charge passed from fastener to panel compared to simple exposure of galvanic panels. Post-exposure, optical profilometry analysis will be conducted to ascertain volume, depth, and area of attack, which may then be utilized in the development of damage functions for galvanic corrosion degradation based on a variety of variables. Acknowledgement: This work was supported by the Office of Naval Research through award number N00014-13-1-0738.

Effect of surface preparation on the corrosion resistance of friction stir linear lap welded AZ31B-H24

ABSTRACTThe effect of surface preparations on the atmospheric (continuous NaCl salt fog) corrosion resistance of bare (uncoated) linear friction stir lap welded magnesium (Mg) alloy AZ31B-H24 joints was investigated. The surface preparations evaluated included as-received (as-welded for the weld zones), mechanically abraded and acid-cleaned. Electrochemical potentiodynamic polarisation, X-ray photoelectron spectroscopy and Auger electron spectroscopy measurements were made to elucidate the link between the surface preparation and the relative corrosion resistance observed across the microstructural zones of the joints. Heavy metal surface contamination of the as-received material, rather than the air-formed oxide or differences in alloy grain size resulting from variations in thermo-mechanical processing history, was found to be the controlling factor affecting the corrosion mode observed and, in turn, the relative corrosion resistance across the joint. Removal of the heavy metal contamination changed the corrosion mode from pit-like to filament-like, which in turn homogenised the corrosion resistance across the joint in the continuous salt fog exposure.

Observation Analysis on the Characteristics of Meteorological Elements and Pollutants During a Continuous Fog and Haze Episode in Spring in Jiaxing City

A continuous fog and haze episode occurred on 17-20 May, 2015 in Jiaxing. Trace gases (O3, CO, SO2 and NO2), PM10, PM2.5, aerosol number concentration in the range of 10 nm-10 μm, meteorological elements, and radiosonde data from the 17st to the 22st of May were used to analyze the formation mechanism and pollutant characteristics during this episode. The results showed that subtropical high pressure lifted northward, a field pressure was dominant over Jiaxing leading to a weak ground wind speed, and a strong inversion layer occurred, this supplied moisture, power and thermal conditions for the occurrence and maintenance of the event. The episode included one precipitation process and two fog processes (rainy fog and radiation-advection fog). During the fog and haze process, the concentrations of NO2, CO, PM10 and PM2.5 were high and the levels of SO2 and O3 were low. Strong precipitation had greater scavenge effects on PM10, PM2.5 and SO2, while weak precipitation aggravated the pollution degree. The PM concentrations increased continuously during the rainy fog process, while it decreased firstly and then increased during the radiation-advection fog process. The spectral distributions of aerosol number concentration were unimodal and differed significantly under different types of weather conditions. The peaks of number concentration were located at 20-30 nm, 100 nm, 30-60 nm, 120 nm, 90 nm under clean, precipitation, fog and haze, rainy fog, radiation-advection fog conditions, respectively. The spectra of surface area concentration were trimodal under clean, precipitation, fog and haze, rainy fog conditions, and had four peaks under radiation-advection fog condition.

The Influence of Emotion and Gender on Work Efficiency in Hazy Weather

In recent years, the eastern part of China has suffered numerous large-scale continuous fog and haze, which seriously impact people’s production and life. In present research, a combination method of questionnaire and experiment is used to discuss whether the hazy weather could in-fluence the emotion and if there are any impacts on the work efficiency. 2 (gender) × 3 (emotional type: positive, neutral and negative) completely randomized design is used and the reaction time (RT) is analyzed. The results show that 1) hazy weather truly induces the negative emotion, e.g. depression and anxiety; 2) the interaction effect of emotion and gender is significant; the RT of females is significantly longer than males’ in negative emotion condition; for females, RT in negative emotion condition is significantly longer than that in positive and neutral emotion condition, which shows that the hazy weather would lead some inefficiency.

The reconstruction of abnormal segments in HJ-1A/B NDVI time series using MODIS: a statistical method

HJ-1A/B is the first small satellite constellation built by China for environmental and disaster monitoring and forecasting. The satellite group has a 2-day repetition cycle and 30 m spatial resolution (charge coupled device camera). Thus, HJ-1A/B can provide hyper-temporal normalized difference vegetation index (NDVI) time series with a medium–high spatial resolution. However, the quality of the HJ NDVI time series can be abnormally low due to a number of factors, such as cloud cover, continuous fog, and haze. In the rainy season or in areas with serious atmospheric pollution, low-quality series often appear in succession, which is referred to as an abnormal segment. Neither the composition method nor quality flags satisfactorily solve this problem; therefore, a large amount of noise and long periods of abnormally low values often remain in HJ NDVI time series. This article presents a method to reconstruct the abnormal segments in HJ NDVI time series with the assistance of Moderate Resolution Imaging Spectroradiometer (MODIS) NDVI time series. The cointegration test was adopted to decide whether MODIS can be used for the reconstruction of NDVI time series for the corresponding HJ image pixels. Statistical quality control methods were used for singling out the abnormal segments in the HJ NDVI time series and establishing an error correction model that combines MODIS and HJ NDVI time series to perform the reconstruction. The study area is located in Jiangsu Province, China. Four-year (2009–2012) HJ multispectral images that cover the study area were used. The results show that abnormal segments in the HJ NDVI time series can be corrected using the proposed method. In a particular year, this method can decrease the root mean square error between the HJ NDVI time series and the reference sequence by 52.5%.

Cause Analysis of Two Continuous Serious Fog and Haze Weather in Wuhan Area

Cause Analysis of Two Continuous Serious Fog and Haze Weather in Wuhan Area

Gene response in rice plants treated with continuous fog influenced by pH, was similar to that treated with biotic stress.

BackgroundThroughout Asia, including Japan, rice plants are cultivated in a wide range of areas from lowlands to highlands and are frequently exposed to fog, including acid fog. Some physiological studies have shown that acid fog can be a stress factor for plants. We analyzed the gene expression profiles of rice plants treated with artificially prepared simulated acid fog (SiAF) or simulated neutral fog (SiNF) for 1 or 7 days.ResultsMicroarray analysis results suggested that both the SiAF and the SiNF treatments induced the expression of genes involved in the defense and stress responses in rice plants. Induction of such genes was detected in plants treated with SiAF for 1 day, and the number of induced genes increased in plants treated with SiAF for 7 days. The genes for defense and stress responses were also induced by SiNF for 7 days, although they were not induced by SiNF for 1 day. The gene expression profiles of the SiAF-treated and the SiNF-treated plants were compared to those of plants treated with other stress factors. The comparison revealed that both SiAF and SiNF treatments have similar effects to biotic stresses and ozone stress. The genes encoding NADPH oxidase and germin, which function in apoplasts, were also induced by SiAF, SiNF and biotic stresses.ConclusionsThese findings suggest that both the SiAF and the SiNF treatments may result in oxidative stress through the apoplastic production of reactive oxygen species.

Fog Collection: Facile and Large‐Scale Fabrication of a Cactus‐Inspired Continuous Fog Collector (Adv. Funct. Mater. 21/2014)

Fog Collection: Facile and Large‐Scale Fabrication of a Cactus‐Inspired Continuous Fog Collector (Adv. Funct. Mater. 21/2014)

Facile and Large‐Scale Fabrication of a Cactus‐Inspired Continuous Fog Collector

Although clean drinking water is a basic human need, freshwater scarcity has been identified as a major global problem of the 21st century. Nature has long served as a source of inspiration for human beings to develop new technology. The cactus in the desert possesses a multifunctional integrated fog collection system originating from the cooperation of a Laplace pressure gradient and the wettability difference. In this contribution, inspired by the cactus, an artificial fog collector on a large scale is first fabricated through integrating cactus spine‐like hydrophobic conical micro‐tip arrays with the hydrophilic cotton matrix. The novel cactus‐inspired fog collector can spontaneously and continuously collect, transport, and preserve fog water, demonstrating high fog collection efficiency and promising applications in the regions with drinking water scarcity. Furthermore, the present approach is simple, time‐saving and cost‐effective, which provides a potential device and new idea to solve the global water crisis.

Fog detection using geostationary satellite data: Temporally continuous algorithm

A fog detection algorithm that uses geostationary satellite data has been developed and tested. This algorithm focuses on continuous fog detection since temporal discontinuities, especially at dawn and dusk, are a major problem with current fog detection algorithms that use satellite imagery data. This is because the spectral radiance at 3.7 μm contains overlapping emissive and reflectance components. In order to determine the radiance at 3.7 μm under fog conditions, radiative transfer model simulations were performed. The results showed that the radiance at 3.7 μm obviously varies with the solar zenith angle, and the brightness temperature differences between 3.7 μm and 10.8 μm are completely dissimilar between day and night (positive and varying with the angle during the daytime, but negative and constant at night). In this algorithm, a dynamic threshold is used as a function of the solar zenith angle. Moreover, additional criteria such as infrared, split-window channels, and a water vapor channel are used to remove high-level clouds. Also, the visible reflectance (0.67 μm) channel is used in the daytime algorithm because visible channel images are very practical for confirming a fog area with the high reflectivity and the smooth texture. The clear-sky visible reflectance for the previous 15 days was also employed to eliminate the surface effect that appeared during dawn and dusk. As the results, fog areas were estimated continuously, allowing the lifecycle of the fog system, from its development to decline, to appear obviously in the resulting images. Moreover, the estimated fog areas matched well with surface observations, except in a high latitude region that was covered by thin cirrus clouds.

Evidence for global circuit current flow through water droplet layers

Foggy air and clear air have appreciably different electrical conductivities. The conductivity gradient at horizontal droplet boundaries causes droplet charging, as a result of vertical current flow in the global atmospheric electrical circuit. The charging is poorly known, as both the current flow through atmospheric water droplet layers and the air conductivity are poorly characterised experimentally. Surface measurements during three days of continuous fog using new instrument techniques show that a shallow (of order 100 m deep) fog layer still permits the vertical conduction current to pass. Further, the conductivity in the fog is estimated to be approximately 20% lower than in clear air. Assuming a fog transition thickness of one metre, this implies a vertical conductivity gradient of order 10 fS m −2 at the boundary. The actual vertical conductivity gradient at a cloud boundary would probably be greater, due to the presence of larger droplets in clouds compared to fog, and cleaner, more conductive clear air aloft.