Atmospheric Band Research Articles

Switchable daytime radiative cooling and nighttime radiative warming by VO2

With the increasing prominence of energy issues, the radiative thermal management techniques hold great potential in sustainable energy research, which attracted much attention. In this study, a temperature-adaptive selective emission structure is proposed to control the phase transition state of doped vanadium dioxide (VO2) by the difference of daytime and nighttime temperatures to achieve all-day radiative thermal management. During the day, the ambient temperature increases. When the VO2 temperature exceeds the phase transition temperature, the structure has high reflectivity in the solar spectral band and high emissivity in the atmospheric transparent band (8–14 μm), resulting in radiative cooling. At night, the ambient temperature decreases. When the temperature of VO2 is lower than the phase transition temperature, the structure has low emissivity in the atmospheric transparent band (8–14 μm) and high absorptivity in the atmospheric radiative bands (5–8 and 14–16 μm), thus realizing the warming effect. Additionally, the impact of variation in material thickness and angle of incidence on the spectral characteristics of the designed structures are also investigated, and the results indicated that the impact on the spectral characteristics of the structures are not significant. This study provides an innovative approach to regulating energy efficiency in buildings, vehicles and utilities, which can help to promote diversity in energy utilization.

Etching Processing of InGaAs/InAlAs Quantum Cascade Laser

The 3–5 μm mid-infrared band is the atmospheric window band, where there are absorption peaks of many molecules. It plays an important role in trace gas detection, directional infrared countermeasures, biomedicine, and free-space optical communications. The wet etching process of the designed InGaAs/InAlAs quantum cascade laser with superlattice structure was explored to provide a good experimental basis for the research and development of lasers. The HBr:HNO3:H2O series of etching solutions were selected for corrosion experiments, and the surface morphology was observed by scanning electron microscopy (SEM) and metallographic microscopy to obtain the corrosion rate of the etching solution. The experimental results show that the etching liquid ratio is HBr:HNO3:H2O = 1:1:10, and the etching rate is 0.6 μm/min. A quantum cascade laser that works continuously at room temperature was prepared, with an injection strip width of 7 μm, a cavity length of 4mm, and an operating temperature of 20 °C. The device works in continuous mode (CW), with a maximum continuous output power of about 186 mW, a threshold current of about 0.4 A, a threshold current density of about 1.428 kA/cm2, a device center wavelength of about 4424 nm, a side mode suppression ratio of 28 dB, and a spectrum full width at half maximum of 2 nm.

Self-adaptive radiation recuperator with double phase transition temperature switches based on VO2 intelligent films

Developing renewable energy for heating and cooling to achieve carbon neutrality and environmental protection is of great significance. The combination of photothermal (PT) and radiative cooling (RC) technology to continuously obtain energy throughout the day is gradually attracting interest, in which vanadium dioxide (VO2) intelligent phase transition film serves as a bridge between the daytime PT mode and the nighttime RC mode. The high phase transition temperature of VO2 poses a challenge to environmental adaptability and dynamic switching in practical applications. In this work, a novel self-adaptive radiation recuperator with double phase transition temperature (37 °C and 68 °C) switches is proposed to exchange energy from the sun and outer space by radiation. Compared with VO2 and W-doped VO2 single-layer structure, this method has a higher self-adaptability to easily achieve the phase transition temperature of mode switching. The absorptivity of the radiation recuperator is 0.75 in the solar band (0.3–2.5 μm), and the emissivity switching capability is present from 0.3 to 0.86 in the atmospheric window band (8–14 μm). The transition mode generated by the presence of double phase transition temperature improves temperature self-adaptability and improves energy collection efficiency in dynamic environments.

Cellulose acetate hierarchical porous coated textile with passive daytime radiative cooling, flexibility and durability

Passive daytime radiative cooling technology is a highly efficient cooling technology with zero energy consumption. When utilized for personal thermal management, radiative cooling textiles are capable of finely regulating the temperature of the human skin microenvironment. This study presents a cellulose acetate (CA) hierarchical porous coated textile that accomplishes high reflectance of sunlight over the full wavelength range, with a low cost and scalability, and a simple preparation procedure. With a high reflectance of 0.91 in the solar wavelength band and a high emissivity of 0.95 in the atmospheric window wavelength band, the CA hierarchical porous coated textile offers exceptional spectrally selective performances. It manifests a subambient cooling temperature of up to 19.0 °C and a skin overheating prevention effect of up to 4.2 °C. Furthermore, the coated textile possesses promising abrasion resistance, acid-alkali corrosion resistance, and mechanical properties. The present work provides a facile path for the development of green-based radiative cooling coated textiles.

Microstructured flexible polymer films with embedded phosphor for multifunctional passive radiative cooling

Abstract Passive daytime radiative cooling schemes are of much interest because of their attractive potential to reduce energy consumption. However, the structural conditions for designing and fabricating efficient radiative cooler limit their optical diversity and hinder their practical utilization (e.g. light-emitting cooling panels, smart window systems, smart signboards, or anticounterfeiting). Here, multifunctional passive radiative cooling films are demonstrated by simultaneously implementing speckle image holography disordered microstructures and phosphor particles into the radiative polymer layer. The as-obtained multifunctional film exhibits high total reflectivity in the sunlight region (∼89%) and strong infrared emissivity (∼91%) within the atmospheric window band (8–13 μm), thus achieving subambient cooling of ∼4.1 °C under direct sunlight in a nonvacuum setup. Interestingly, the multifunctional structural films can be acted as light-emitting films under violet or blue illumination and also can be easily patterned by drawing, cutting or pixelating. The multifunctional structured films demonstrated here can be utilized for potential UV resistance, smart window displays, anticounterfeiting cooling systems, roofing materials and certain aesthetic purposes.

Optical-thermal modeling and geographic analysis of dusty radiative cooling surfaces

Radiative cooling for energy conservation and harvesting has gained considerable attention worldwide in recent years. The optical and thermal characteristics of radiative cooling surface at outdoors is susceptible to dust soiling. Currently, limited research has been devoted to this problem. This work presents a model utilizing the beam envelope method and effective medium theory to investigate the optical characteristics of radiative cooling surfaces impacted by dust soiling. Subsequently, an optical-thermal coupling model is developed to investigate the spectral emissivity, average absorption/emission rates, and net heat gain of radiative cooling surfaces affected by dust soiling. The effect of dust soiling on the absorption of solar radiation is evident, with a substantial effect observed, but its impact on emissivity in the atmospheric window bands is comparatively minor. Meanwhile, it could be noticed that the mechanisms by which various material parameters of dust layers impact optical characteristics are different. In addition, the integration of the optical-thermal coupling model with EnergyPlus meteorological data and MERRA-2 facilitates an exploration of the geographical distribution of radiative cooling power variations induced by dust soiling across different regions in China. It is concluded that regions in China with a higher potential for radiative cooling often characterized by elevated dust deposition rates and low precipitation, rendering them more susceptible to the adverse effects of dust soiling. Effective cleaning significantly enhances both the optical and thermal characteristics of radiative cooling surfaces. The findings of this study offer a theoretical foundation for the enduring application of radiative cooling technology.

Superhydrophobic Composite Coatings Can Achieve Durability and Efficient Radiative Cooling of Energy-Saving Buildings.

Passive daytime radiative cooling (PDRC) technology has received a great deal of attention in the field of energy efficiency and environmental protection as a sustainable technology and a large-scale and promising solution to mitigate the environmental impact of global warming. In this study, we prepared PDRC material by combining FEP with modified Al2O3 particles and using the method of spray combined with phase separation. The synergistic effect of the formed surface micronanostructures, combined with the molecular vibration of FEP and the phonon polarization resonance of Al2O3, further improves the optical performance of the PDRC coating. The PDRC coating has an average reflectivity of 0.96 in the solar spectral band (0.3-2.5 μm) and an average emissivity of 0.963 in the atmospheric window band ((8-13 μm). In addition, the PDRC coating had good hydrophobicity, and its water contact angle (WAC) reached 159.3°. Under direct sunlight conditions, PDRC materials have a good temperature drop (4.9 °C) compared to ambient temperatures and radiative cooling power (81.2 W/m2). The prepared coating maintains superhydrophobicity and excellent cooling performance when soaked in solutions of different pH values and UV radiation, which was of great significance for sustainable applications. Our work provides a form of long-term cooling that can be effectively implemented in green and energy-efficient buildings.

Performance and Relative Humidity Impact of Cellulose‐Derivative Networks in All‐Day Passive Radiative Cooling

AbstractAll‐day passive daytime radiative coolers (PDRC) offer a promising solution for energy‐free cooling of buildings and devices. This study investigates the use of various cellulose‐derivative networks to achieve optimal and stable cooling performance. These results showed that the mixed cellulose ester network has a maximum solar reflectance of 97%. While cellulose acetate network has a maximum infrared emissivity of 96% in the atmospheric transparency window band, which is a near‐perfect infrared emitter, the nitrocellulose network shows the highest cooling temperature, with a significant reduction of 14 °C from the ambient temperature and a power of 124 W·m−2 during the daytime and at night of 7.7 °C and 72.8 W·m−2. This study also analyzes the dampness's effect on the cooling performance of cellulose‐derivative networks. The cooling performance of the nitrocellulose network drops ≈ 3 °C (from 14 to 11.3 °C) when the relative humidity of the day exceeds ≈ 30% is observed. These findings indicate that the capacity of a material to absorb water from the surrounding air significantly influences its performance as a passive cooler, primarily due to changes in its optical properties. This is an important insight, as it highlights the need to consider environmental factors like relative humidity and sample hydrophobicity for PDRC systems.

Photopolymerized PAM/CTS/SA/Ca2+/TiO2 hydrogel for sustainable passive cooling

Evaporative cooling and radiative cooling are considered to be energy-saving and environmentally friendly cooling technologies. However, the evaporative cooling system requires complex external water supply equipment, and the radiative cooling is susceptible to weather, which hinder the practical application. Herein, TiO2 was used as the photo-initiator and spectral regulator, and a hydrogel integrating radiative cooling and evaporative cooling was prepared by combining photopolymerization with semi-acidification sol–gel transition method. The obtained hydrogel shows good mechanical strength (elongation at break > 600 %, and fracture stress > 200 kPa), high visible reflectance (>80.0 %) and emissivity in atmospheric window band (>90.0 %). At the same time, due to the introduction of hygroscopic agent CaCl2, it can replenish water itself at night. In outdoor experiment, the hydrogel showed a cooling effect of up to 12.5 °C, showing a significant potential for reducing energy consumption in cooling applications. In addition, the synthesis process of hydrogel is green, which aligns with environmental safety and sustainability goals. This study provides a new strategy for developing efficient, environmentally friendly, and low-cost passive coolers to reduce the global energy burden.

Spectrally selective radiation infrared stealth based on a simple Mo/Ge bilayer metafilm

In this paper, we propose and demonstrate a spectrally selective radiation infrared stealth metafilm based on a simple bilayer structure. Specifically, we use the common inexpensive metal Mo instead of traditional precious metals and achieve selective thermal radiation in the infrared band. In the atmospheric window band, the absorptivity is relatively low, which can well achieve the purpose of infrared stealth, while in the non-atmospheric window band, the absorptivity acutely increases, with a high absorptivity of 94.89 % at 6.04 μm, which can achieve better radiation heat dissipation. The experimental results are consistent with the simulation. The average emissivity in the 8–14 μm atmospheric window band is 0.32, while in the 5–8 μm non-atmospheric window band is 0.80, which proves the possibility of its practical application. Meanwhile, the metafilm proposed by us can be easily fabricated and can be widely used in the control of infrared thermal radiation, thermal management, and thermal camouflage, which has a very promising application prospect.

Geographical and seasonal variations of gravity wave activities in the upper mesosphere measured by space-borne imaging of molecular oxygen nightglow

Geographical and seasonal variations of gravity wave events in the upper mesosphere were investigated using the nightglow imaging data obtained by the Visible and near-Infrared Spectral Imager (VISI) on the Ionosphere, Mesosphere, upper Atmosphere and Plasmasphere (IMAP) onboard the International Space Station (ISS). The nadir-imaging data of the O2(0–0) atmospheric band (762 nm) with the typical emission peak around 95 km altitude was used to investigate small-scale waves (horizontal wavelengths less than ~ 200 km) on a global scale. To detect gravity wave events, the variance of high-pass filtered nightglow images within a local 100 km radius was evaluated, with a threshold set at three times the standard deviation from the average variance of the background level. A data screening algorithm that evaluates the variance of upwelling contamination light emission was also introduced to remove contaminated data. Applying the variance filter and data screening algorithm to a nearly 3-year data set, from November 2012 to August 2015, occurrence maps of wave events for four seasons were derived. The occurrence maps show a higher frequency of wave events in winter high latitudes (> 40° N/S), considerably attributed to gravity wave activity associated with the polar night jet. Hot spots were observed near orographic sources in winter high latitudes, including the eastern part of North America, Europe, and the southern Andes. In the summer hemisphere, hot spots were detected at mid-to-high latitudes such as North America, Europe, and the eastern side of the Eurasian continent, and at equatorial latitudes just above the intertropical convection zone (ITCZ). They are likely gravity waves from deep convection that arise from mid-latitude summertime thunderstorms and the ITCZ, respectively. During the equinox seasons, hot spots were detected near convective sources such as the Amazon Rainforest, Congo Rainforest, and the Indochina peninsula.Graphical

CloudbandPy 1.0: an automated algorithm for the detection of tropical–extratropical cloud bands

Abstract. Persistent and organized convective cloud systems that arise in convergence zones can lead to the formation of synoptic cloud bands extending from the tropics to the extratropics. These cloud bands are responsible for heavy precipitation and are often a combination of tropical intrusions of extratropical Rossby waves and processes originating from the tropics. Detecting these cloud bands presents a valuable opportunity to enhance our understanding of the variability of these systems and the underlying processes that govern their behavior and that connect the tropics and the extratropics. This paper presents a new atmospheric cloud band detection method based on outgoing longwave radiation using computer vision techniques, which offers enhanced capabilities to identify long cloud bands across diverse gridded datasets and variables. The method is specifically designed to detect extended tropical–extratropical convective cloud bands, ensuring accurate identification and analysis of these dynamic atmospheric features in convergence zones. The code allows for easy configuration and adaptation of the algorithm to meet specific research needs. The method handles cloud band merging and splitting, which allows for an understanding of the life cycle of cloud bands and their climatology. This algorithm lays the groundwork for improving our understanding of the large-scale processes that are involved in the formation and life cycle of cloud bands and the connections between tropical and extratropical regions as well as evaluating the differences in cloud band types between different ocean basins.

Intensities of Atmospheric bands of molecular oxygen in the nightglow

The intensities of the Atmospheric bands of molecular oxygen Ivʹvʺ (cm–2s–1) in the nightglow of the Earth’s atmosphere are calculated for different latitudes and seasons. The calculations were performed using experimental data on the profiles of atomic oxygen concentrations for different seasons. The calculated integral intensities of Atmospheric bands are compared with experimental data obtained from the space shuttle (STS transport system), as well as from the Keck I telescope. It is shown that there is good agreement between theoretical calculations and experimental data for the considered latitudes, but better agreement is received with data obtained from Keck I telescope.

Intensities of the Atmospheric Bands of Molecular Oxygen in the Nightglow

Intensities of the Atmospheric Bands of Molecular Oxygen in the Nightglow

The design and performance research of PTFE/PVDF/PDMS superhydrophobic radiative cooling composite coating with high infrared emissivity

High infrared emissivity in the atmospheric transparent spectral band, high reflectivity in the solar radiation band, self-cleaning and no heat treatment process are crucial for the application of the radiative cooling materials. In this work, a superhydrophobic radiative cooling composite coating was facilely prepared by using two sizes of polytetrafluoroethylene (PTFE) particles as main fillers and silica (SiO2) nanoparticles as auxiliary fillers, and polydimethylsiloxane (PDMS) and polyvinylidene fluoride (PVDF) as binders. The coating can be scraped onto the substrate through a scraper without any heat treatment procedure. The water droplet contact angle (WCA) and rolling angle (SA) of the coating can reach a maximum of 158 ± 0.5° and a minimum of 3 ± 0.3°, respectively. The average reflectance of the coating in the visible spectral band was around 90.6%. The average infrared emissivity of the coating in 8 ∼ 13 µm spectral band was about 0.989. The test results show that the coating has excellent self-cleaning and cooling properties. Furthermore, the coating also exhibits good abrasion resistance, preferable adhesion performance, ultraviolet radiation resistance, high temperature stability, self-cleaning and anti-icing performance.

Theoretical study of a highly fault-tolerant and scalable adaptive radiative cooler.

Conventional static radiative coolers have an unadjustable cooling capacity, which often results in overcooling in low temperature environment. Therefore, there is a great need for an adaptive dynamic radiative cooler. However, such adaptive coolers usually require complex preparation processes. This paper proposes an adaptive radiative cooler based on a Fabry-Perot resonant cavity. By optimizing the structural parameters of the radiative cooler, this adaptive radiative cooler achieves a modulation rate of 0.909 in the atmospheric window band. The net radiative cooling performance difference between low and high temperatures is nearly eight times. Meanwhile, the device is easily prepared, has a high tolerance, and can effectively prevent W-VO2 oxidation. This study provides new insights into adaptive radiative cooling with potential for large-scale applications.

On-chip integrated polarization spectral imaging device for atmospheric infrared band

On-chip integrated polarization spectral imaging device for atmospheric infrared band

Laser-compatible infrared stealth metamaterial based on high-temperature resistant metal

In this paper, we design a metamaterial film with multilayer structure for laser-compatible infrared stealth. The multilayer film structure is formed by stacking the high-temperature resistant metal Mo and Ge. Numerical results indicate that the absorptivity is 80.42 % and 96.92 % at 1.06μm and 1.55μm, respectively and the average emissivity of 35μm and 812μm atmospheric window bands are lower than 20 %. At the same time, there is a wide-band resonant absorption peak at the 5 ∼ 8 μm non-atmospheric window band which is beneficial for radiant heat dissipation. The effects of film thickness, polarization of incident light as well as incident angles on stealth performance are studied. The designed structure is only composed of four layers, which is easy to fabricate by film deposition and to realize large-scale integration, and has a very broad application prospect.

Multispectral camouflage nanostructure design based on a particle swarm optimization algorithm for color camouflage, infrared camouflage, laser stealth, and heat dissipation.

With the development of camouflage technology, single camouflage technology can no longer adapt to existing environments, and multispectral camouflage has attracted much research focus. However, achieving camouflage compatibility across different bands remains challenging. This study proposes a multispectral camouflage metamaterial structure using a particle swarm optimization algorithm, which exhibits multifunctional compatibility in the visible and infrared bands. In the visible band, the light absorption rate of the metamaterial structure exceeds 90%. In addition, color camouflage can be achieved by modifying the top cylindrical nanostructure to display different colors. In the infrared band, the metamaterial structure can achieve three functions: dual-band infrared camouflage (3-5 µm and 8-14 µm), laser stealth (1.06, 1.55, and 10.6 µm), and heat dissipation (5-8 µm). This structure exhibits lower emissivity in both the 3-5-µm (ɛ=0.18) and 8-14-µm (ɛ=0.27) bands, effectively reducing the emissivity in the atmospheric window band. The structure has an absorption rate of 99.7%, 95.5%, and 95% for 1.06, 1.55, and 10.6 µm laser wavelengths, respectively. Owing to its high absorptivity, laser stealth is achieved. Simultaneously, considering the heat dissipation requirements of metamaterial structures, the structural emissivity is 0.7 in the non-atmospheric window (5-8 µm), and the heat can be dissipated through air convection. Therefore, the designed metamaterial structure can be used in military camouflage and industrial applications.

Night-time radiative warming using the atmosphere

Night-time warming is vital for human production and daily life. Conventional methods like active heaters are energy-intensive, while passive insulating films possess restrictions regarding space consumption and the lack of heat gain. In this work, a nanophotonic-based night-time warming strategy that passively inhibits thermal radiation of objects while actively harnessing that of atmosphere is proposed. By using a photonic-engineered thin film that exhibits high reflectivity (~0.91) in the atmospheric transparent band (8–14 μm) and high absorptivity (~0.7) in the atmospheric radiative band (5–8 and 14–16 μm), temperature rise of 2.1 °C/4.4 °C compared to typical low-e film and broadband absorber is achieved. Moreover, net heat loss as low as 9 W m−2 is experimentally observed, compared to 16 and 39 W m−2 for low-e film and broadband absorber, respectively. This strategy suggests an innovative way for sustainable warming, thus contributes to addressing the challenges of climate change and promoting global carbon neutrality.