Moist Air Research Articles

Subseasonal Variation Characteristics of Low-Cloud Fraction in Southeastern and Northwestern North Pacific

The subseasonal variability of the low-cloud fraction (LCF) over the southeastern North Pacific (SENP) and northwestern North Pacific (NWNP) was studied using satellite observations and the European Centre for Medium-Range Weather Forecasts (ECMWF) reanalysis. It is found that subseasonal variability of the LCF was closely related to variations in the estimated inversion strength (EIS), sea surface wind speed (SSW), sensible heat flux (SHF), sea surface temperature (SST), surface temperature advection (Tadv), relative humidity (RH), surface level pressure (SLP) and surface air temperature (SAT). An increase in the LCF over the SENP is associated with the development of an anomalous anticyclonic circulation, which is located on the west coast of America. The cold advection, together with the subsidence warming associated with the anticyclonic circulation, strengthens the temperature inversion, favoring the development of the LCF. In the NWNP, the maximum LCF anomaly was also correlated with the stable boundary layer. The southerly wind blows airflow over the Kuroshio Extension from the subtropics, which brings warm and moist air. When air flows to the colder sea surface, it is cooled and condensed by the intensified heat exchange. A lead-lag composite analysis indicates that the mechanisms are different between the SENP and the NWNP, possibly due to the different types of low-level clouds over these two regions. In the SENP, the trade cumulus dominates under a strong capping inversion over the subtropics, whereas fog and stratus often occur under a shallow capping inversion in the NWNP. The effects of atmospheric circulation are also discussed.

A flexible device to produce a gas stream with a precisely controlled water vapour mixing ratio and isotope composition based on microdrop dispensing technology

Abstract. ​​​​​​​Here we describe a versatile device to produce a gas stream with a precisely controlled water vapour mixing ratio and stable water isotope composition based on microdrop dispensing technology. To produce a moist airstream, the microdrop dispensing technology ejects micrometre-size water droplets that completely evaporate into a stream of carrier gas heated to 60 ∘C. By precisely controlling the contribution of water standards from two dispenser heads into a carrier gas stream, the device allows one to set the air–vapour stream to any isotope ratio between two endmember waters. We show that the Allan deviation of the water vapour mixing ratio is 10 ppmv over more than 24 h and reaches 0.004 ‰ for δ18O and 0.02 ‰ for δ2H for a flow rate of 40 sccm. Tests with flow rates from 40–250 sccm show an increase of the Allan deviation with higher flow rates. Tests with mixing standard water from two dispenser heads show a linear mixing across a range of water vapour mixing ratios from 1000 to 20 000 ppmv. In addition to presenting the design and several performance characteristics of the new system, we describe two application examples. First, we utilise the device to determine the water vapour mixing ratio–isotope ratio dependency, a common artefact of water vapour isotope spectrometers. Second, we utilise the device to provide a constant background stream of moist air for fluid inclusion water isotope analysis in calcite samples from stalagmites. The observed flexibility and precision of the device underpins its usefulness and potential for a wide range of applications in atmospheric water vapour isotope measurements. Future developments could focus on reducing the number of manual interventions needed to clear dispenser heads from gas bubbles and the provision of a water vapour stream at flow rates of up to several litres per minute.

The Role of Local and Remote Processes for Wintertime Surface Energy Budget Extremes over Arctic Sea Ice

Abstract Arctic warm extremes and anomalous sea ice melting have been linked to episodic injections of warm and moist air from midlatitudes, as well as airmass transformations inside the Arctic. However, the relative importance of remote and local processes for such events remains unclear. Here, we focus on events with extreme positive daily-mean surface energy budget (SEB) anomalies over Arctic sea ice in ERA5 data during extended winters (November–March during 1979–2020). Kinematic backward trajectories from the tropospheric column collocated with the SEB anomalies show that near-surface air is of Arctic origin, whereas air farther aloft is transported poleward from the midlatitudes and ascends. Despite the different origin of the air, the entire tropospheric column shows pronounced potential temperature anomalies (on the order of 10 K) building up along air-parcel trajectories over 2–4 days. Quantifying the contributions of horizontal and vertical transport as well as diabatic processes to the generation of these potential temperature anomalies emphasizes the relevance of horizontal advection across the climatological potential temperature gradient for the generation of the anomalies at all levels. Anomalies aloft are further enhanced by latent heating and those near the surface by subsidence, respectively. Surface heat fluxes over subpolar and polar oceans are key for warming and moistening the near-surface air of predominantly Arctic origin and maintaining a positive potential temperature anomaly, which due to its proximity to the surface unfolds the strongest impact on the SEB. This suggests that Arctic airmasses and their local transformations are crucial for generating the most extreme SEB anomalies.

SAXS Application for the Determination of the Gold Nanoparticle Sizes in Au/C Catalysts: Advantages over Other Methods

In the case of Au/C catalysts have been shown advantages of application SAXS with masking liquid technique for determining supported metal particle sizes compared with TEM and XRD as standard methods. According to SAXS data particle size distributions of gold in a wide range (1–50 nm) were obtained with full consideration of all size fractions of particles present in the samples under study. Also values of the mass fraction of “X-ray amorphous” gold particles with size less than 4 nm (WSAXS) were determined. It has been found that the oxidative treatment of the carbon support before deposition of metallic gold precursor complexes has a significant effect on the size distribution of gold particles in the final catalyst. Comparison of the results of measuring the rate of CO oxidation by an excess of moist air at 40°C on Au/C catalysts with the (WSAXS) values found for these catalysts showed that the catalytic activity increases exponentially as (WSAXS) increases. High activity in CO oxidation reaction was demonstrated by Au/C catalysts with (WSAXS) ≥ 80%.

Signatures of Oceanic Wind Events in Convection-Resolving WRF Model Simulations

Abstract Analyses of cloud-top temperature and lightning characteristics of 48 Weather Research and Forecasting (WRF) Model–simulated ocean-based wind events, with 1-min temporal and 0.5-km horizontal resolution, revealed signatures similar to the corresponding 13 observed events detected by buoys and Coastal-Marine Automated Network (C-MAN) stations as shown in prior research on ocean-based wind events by the first author. These events occurred in the eastern Gulf of Mexico and in the Atlantic Ocean from Florida northward through South Carolina. The coldest WRF cloud-top temperature (WCTT) and peak WRF-estimated lightning flash rate values of the model-simulated events, where each event was required to have a negative vertical velocity of at least 10 m s−1 in the lowest 2 km associated with a convective storm, occurred at an average of 4.2 and 1.1 min prior to the events, respectively. With 36 of the events, the peak estimated flash rate occurred within 5 min of the coldest WCTT. Cloud depth typically increased as the WCTT decreased, and the maximum depth occurred at an average of 2.9 min prior to the events. Thermal cooling and precipitation loading provided negative buoyancy needed to help drive the wind events. Environmental characteristics of the model-simulated ocean-based wind events also resembled those associated with land-based wet downbursts, including moist air near the surface, lapse rates near moist adiabatic, and low cloud bases.

Numerical study of falling film dehumidification performance on corrugated plates

Due to a number of benefits, liquid desiccant dehumidification has received a lot of attention lately. In comparison to previous improvement strategies, corrugated plates have demonstrated higher efficacy in liquid desiccant dehumidification. This study employs computational fluid dynamics to examine the dehumidification performance of falling film liquid desiccant dehumidification on over sinusoidally shaped corrugated plates. The effects of plate geometries, solution parameters, and moist air (concentration of humidity, temperature, and flow rate) were discussed. Additionally, a mass transfer correlation was proposed based on the current numerical data. It is indicated that the corrugated plate significantly enhances dehumidification performance due to the liquid film waves intensification, mass transfer area expansion, and induction of vortexes close to the gas-liquid interface. The most effective falling film dehumidification is achieved using a corrugated plate with a wavelength of 5.0 mm and an amplitude of 0.5 mm. By raising the solution or air inlet temperature, the dehumidification rate is reduced while being strengthened by raising the solution or air inlet concentration, velocity, or air humidity. While decreasing when solution intake concentration or air velocity rises, the efficacy of dehumidification rises as solution velocity does. The proposed mass transfer correlation accurately predicts 93.3 % of the 45 data, with an error of 11 % or less. In the current parameter scopes, the magnitude has a more significant effect on Shair than the wavelength. Adjustments to air velocity and solution concentration can cause significant fluctuations in Shair, while air and solution temperature have little effect on Shair.

Application of ellipsometry to study the adsorption of corrosion inhibitors on metals from aqueous solutions and vapor phase

Application of ellipsometry to study the adsorption of corrosion inhibitors on metals from aqueous solutions and vapor phase

Indoor air temperature and relative humidity measurements in Finnish schools and day-care centres

Indoor air temperature and relative humidity measurements of schools and day-care centres in two research projects on indoor air conditions in municipal buildings with mechanical ventilation in Finland were combined for a large sample of occupied spaces with typical conditions experienced by users of the buildings. In addition to user experience, the occupied spaces represented the spaces with determining air humidity load when assessing moisture performance of envelope structures. Indoor air temperature was stable excluding extreme external conditions that caused crossings of limit values. Permanence within limit values of the Finnish Classification of Indoor Environment was inadequate leaving all buildings in the lowest classification level S3. Mechanical ventilation in municipal buildings is designed to keep pollutants at moderate level during high occupancy which results in non-existent indoor air moisture excess, which during winter leads to low indoor air relative humidity. Although dry indoor air provides safety of envelope structures, the drawback is poor performance with regards to the recommended range. Dry indoor air has negative effects on the indoor air quality experienced by the users, causing skin and eye irritation.

Immobilization of nanodiamonds onto cotton fabric through polyurethane nanofibrous coatings for summer clothing

AbstractGlobal warming is one of the alarming issues, which is impacting humans globally. It is preferred to adopt a lifestyle that promotes heat dissipation from the human body. One approach to cool a human body is improvement in personal apparel, which can help the human body to cool quickly. The required characteristic for cooling performance can be achieved by employing materials with excellent thermal conductivity. Nanodiamonds (ND) have exceptional thermal conductivity properties and can help overcome the poor thermal conductivity of fabrics. This manuscript presents a study on a one‐sided coated fabric where NDs are applied to the skin side of the fabric to promote heat dissipation toward the atmosphere while the other side of the fabric, exposed to the hot atmosphere, remains uncoated to delay the transfer of out from atmosphere to human body. ND was applied onto cotton fabric through electrospraying polyurethane (PU) and carboxylated ND (NDCOOH). Scanning electron microscope (SEM) and optical microscopy images indicated a homogeneous distribution of the sprayed ND/PU solution over the fabric surface. The samples were chemically analyzed by Fourier transform infrared spectroscopy (FTIR). The thermal resistance was measured by a sweating guarded hot plate (SGHP), which confirmed lower thermal resistance of fabric from the ND‐coated side to atmosphere as compared to control, and thermal resistance from the uncoated to atmosphere was the same for both controlled and treated samples. Similarly, thermal conductivity, radiant heat transfer, and infrared spectroscopy characterizations strengthened the findings of SGHP results. Real‐life simulated experiments were also conducted to verify the performance of developed samples. The electrosprayed samples also showed higher ultraviolet protection than the control sample. Air permeability and moisture absorption of the samples slightly decreased after applying the coating but remained within an acceptable range of comfortability. The developed fabric can promote energy conservation, as it will warm slowly but cool quickly. This allows home or office temperature setpoints for localized cooling to be 2–3°C lower with a projected energy savings between 20% and 30%.

Improved Heat Transfer Modeling of Moist Air Condensation on Hydrophobic Metallic Surface

For dropwise condensation of water over a textured surface, the condensation rate is limited by the conduction resistance of the droplet. Conduction models with varying levels of approximation have been reported in the literature. In the present study, the conduction resistance of a spherical-cap droplet is derived by regression analysis of data generated by 3D numerical simulation. Results show that conduction resistance is sensitive to the choice of contact angle and droplet radius. The proposed model has significant differences from reported models which are based on 1-D and 2-D approximations. An important source of discrepancy is traced to additional heat flux localized at the three-phase contact line. Equivalently, high local heat flux serves to lower thermal resistance between the vapor-liquid interface and the condensing wall. The prediction of the droplet growth rate using the proposed conduction model is in good agreement with the experiments reported in the literature. The improved conduction resistance correlation is incorporated in the model for a space- and time-resolved dropwise condensation cycle for vapor condensing from moist air. Simulations with the improved condensation model show close agreement with experimental data, justifying the utility of an improved correlation for conduction resistance.

Site-specific transfer parameters for the tritium transport model at a tropical site, Tarapur, west coast of India

The study of the fate of atmospheric release and transport of Tritium requires an understanding of the exchange/transfer of Tritium (HTO) from within the compartments; air, soil, and plant systems. The Tritium transfer parameters within these compartments are used in specific activity models to compute TFWT and OBT in terrestrial plants and are highly dependent on the site-specific conditions. Hence a study was carried out to generate site-specific Tritium transport model parameters in the tropical environment of Tarapur which receives the atmospheric releases of Tritium from nuclear facilities operating at this site, on the West coast of India. The paper presents the details of the study carried out in Tarapur, India. The transfer parameters generated through this study are soil water to air moisture HTO transfer ratio: CRs, plant water to air moisture HTO transfer ratio: Rpa, and plant water to soil water HTO transfer ratio: Rpw. The geometric mean and geometric standard deviation (GSD) of the transfer ratios, CRs, Rpa and Rpw determined were found to be 0.50 (GSD: 3.52), 0.53 (GSD: 2.51) and 1.12 (GSD: 2.58), respectively. In addition, the Tritium scavenging ratio, surface loading, and wet deposition velocity were also derived and were found to be 1.59 ± 1.32, 1.21 × 10−2 Bq m−2 s−1, and 7.91 × 10−2 m s−1, respectively. The study has generated a set of site-specific model input parameters for a tropical coastal site of Tarapur, India, and details are discussed in the manuscript.

Hygrothermal Performance of Bio-Based Exterior Wall Constructions and Their Resilience under Air Leakage and Moisture Load

The use of renewable building materials in construction is crucial to minimising the environmental impact of new buildings. Bio-based building materials have a wide range of positive properties, many of which are due to their hygroscopic behaviour. The purpose of this study is to investigate the hygrothermal performance of chopped straw, sheep’s wool, and cellulose insulated timber frame external wall assemblies in the presence of air leakage and high indoor relative humidity. For this purpose, tests with different moisture contents, overpressures, and defects in the airtight layer were carried out in an outdoor test stand over a period of 18 months. The results were compared with a conventional mineral wool insulated construction. Both sheep’s wool and cellulose are particularly fault-tolerant insulation materials in combination with timber frame constructions. All three bio-based insulations, despite defects in the airtight layer, showed no mould-prone moisture content. An installation level insulated with sheep’s wool can increase the fault tolerance of constructions with insulation made of hygric and more sensitive building materials. For chopped straw and cellulose, the measured U-value was lower than expected. Further in situ measurements of bio-based structures are important to gain confidence in their hygrothermal behaviour and to increase their use in multi-storey construction.

Thermodynamic and kinematic drivers of atmospheric boundary layer stability in the central Arctic during the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC)

Abstract. Observations collected during the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) provide a detailed description of the impact of thermodynamic and kinematic forcings on atmospheric boundary layer (ABL) stability in the central Arctic. This study reveals that the Arctic ABL is stable and near-neutral with similar frequencies, and strong stability is the most persistent of all stability regimes. MOSAiC radiosonde observations, in conjunction with observations from additional measurement platforms, including a 10 m meteorological tower, ceilometer, microwave radiometer, and radiation station, provide insight into the relationships between atmospheric stability and various atmospheric thermodynamic and kinematic forcings of ABL turbulence and how these relationships differ by season. We found that stronger stability largely occurs in low-wind (i.e., wind speeds are slow), low-radiation (i.e., surface radiative fluxes are minimal) environments; a very shallow mixed ABL forms in low-wind, high-radiation environments; weak stability occurs in high-wind, moderate-radiation environments; and a near-neutral ABL forms in high-wind, high-radiation environments. Surface pressure (a proxy for synoptic staging) partially explains the observed wind speeds for different stability regimes. Cloud frequency and atmospheric moisture contribute to the observed surface radiation budget. Unique to summer, stronger stability may also form when moist air is advected from over the warmer open ocean to over the colder sea ice surface, which decouples the colder near-surface atmosphere from the advected layer, and is identifiable through observations of fog and atmospheric moisture.

Characteristics and mechanisms of the severe compound cold-wet event in southern China during February 2022

A severe compound cold-wet event occurred in southern China (hereafter referred to as CWESC ) in February 2022, leading to enormous socioeconomic losses. In this study, we proposed a new index to denote the severity of the compound cold-wet event. Based on the multivariate survival method, the CWESC in February 2022 is identified as the severest event during the past six decades. Our results indicate that the CWESC in 2022 is jointly regulated by the La Niña-like SST condition in the tropical Pacific and the warm SST anomalies in the North Atlantic, and a teleconnection in the Northern Hemisphere during winter (hereafter referred to as TNHW) plays the key role. The TNHW pattern originates from the tropical Pacific, and it splits into two routes over the North Atlantic. The northern branch of TNHW propagates via the Arctic and Siberia, causing intensified near-surface northerly wind and partially inducing an anomalous anticyclone over the western North Pacific (WNP). The southern branch of TNHW propagates via the Mediterranean and western Asia, inducing a deepened India–Burma trough and partially inducing the anomalous anticyclone over WNP. The intensified near-surface northerly wind causes enhanced cold advection over southern China, while the deepened India–Burma trough and the anomalous anticyclone over WNP cause increased southerly warm and moist air flow towards southern China, resulting in the CWESC in 2022. Moreover, four groups of numerical experiments forced by tropical Pacific, North Pacific, and North Atlantic SST anomalies are conducted based on the Community Atmosphere Model version 5. The results confirm the important roles of the La Niña-like condition and the warm SST anomalies in the North Atlantic in causing the CWESC in 2022.

Express formation and characterization of SERS-active substrate from a non-degradable Ag-Nb-N-O film

In this work, we propose an original approach for rapid and easy conversion of a thin Ag-Nb-N-O film into surface enhanced Raman scattering (SERS) active substrate. The initial Ag-Nb-N-O substrate has a long shelf life because silver particles are prevalently accumulated inside the film and possess resistivity to degradation. An activation of the substrate is carried out just before the SERS-measurements by a 15-second microwave heating the Ag-Nb-N-O film at 800 W, which facilitates immediate extrusion of internal silver to the surface. This leads to the formation of a dense array of Ag particles that show an improved SERS-activity. We compare SERS-activity of the initial and microwave-treated Ag-Nb-N-O films with that of a control substrate based on Ag nanoparticles grown on the SiO2 surface. Both initial and control substrates are aged in a moist air for 60 days before the SERS-measurements. An intensity of the SERS-signal from 10-5 M 5,5′-Dithiobis(2-nitrobenzoic acid) or DTNB on the activated Ag-Nb-N-O film is approx. 270 higher than that on the control Ag nanoparticles. The TEM and EDS studies of the initial Ag-Nb-N-O film prove its stability to sulfidization while the control Ag nanoparticles are found to bind to sulfur from the moist air.

Numerical analysis on performance of mechanical draft wet cooling towers based on the condensation plume module

To illustrate the characteristics of the mechanical draft wet cooling tower (MDWCT) with the condensation plume module, a 3D numerical model is employed. The two cases, plume abatement with water saving and non-plume-abatement with non-water-saving, are compared, and the analyzed parameters include the ventilation rate, plume generation, water saving rate, and cooling characteristic. Results that the plume abatement and water saving for MDWCT are achieved at the cost by reducing thermal performance, and the outlet water temperature is raised by 1℃ compared with the non-plume-abatement with the non-water-saving condition. For plume abatement with water saving conditions, the air temperature and moisture content in the MDWCT will be reduced twice to achieve plume abatement and water saving. When the inlet water temperature is much higher than the ambient temperature, the plume abatement has become very difficult. The water saving rate is improved as the relative humidity, inlet water temperature and flow rate add, while that is reduced with the ambient air temperature adds. By adjusting the operating parameters, the water saving rate can be reduced to a minimum of 1.35 % and increased to a maximum of 14.95 %.

A different approach to estimate air moisture

When comparing dry and humid air densities and trying to understand which one is denser, the right answer not necessarily follows our intuition. This happens in the Environmental Engineering lectures when students are asked: Is dry or humid air denser? To understand the role of water vapor in air, a method to compute the mass mixing ratio, specific humidity and average molecular weight is presented. This set of equations is more precise than the traditional method and clarifies how water vapor influences physical properties such as air density and bulk molecular weight.

Numerical and experimental investigation on condensation inside a turbine designed for an 100 kW polymer electrolyte membrane fuel cell system

This work presents mathematical modelling of moist air condensation process in a fuel cell turbine. A condensation model based on the classical nucleation theory and the Hertz–Knudsen droplet growth model is established. The numerical approach is validated through experimental results of the MS nozzle and a fuel cell turbine, and the simulation fits the experimental data well. Influences of inlet temperature and pressure on condensation process in the turbine is examined. Results show that increase of inlet temperature apparently weakens condensation and inlet heating can be realized by arranging a gas-to-gas heat exchanger in the air supply subsystem without consuming additional energy. Moreover, at the same mass flow rate increase of inlet pressure reduces the expansion ratio, thereby curbing the condensation. Compared with the matching scheme of a bypass valve, turbocharger matching with a back-pressure valve allows higher inlet pressure to be achieved and can effectively suppress the condensation.

Study on the impacts of refrigerant leakage on the performance and reliability of datacenter composite air conditioning system

Refrigerant leakage occurring in the data center composite air conditioning system could decrease energy efficiency and even results to reliable risks like insufficient cooling and indoor air moisture condensation. In this study, the dynamic model of composite air conditioning system is built to research effects of refrigerant leakage on system performance. Further, influences of outdoor temperature, leakage area and leakage location on system reliability in different modes are investigated. Results indicate that in both modes obvious deviation of superheating degree and evaporating temperature manifest at least 40 % refrigerant has leaked. In vapor compression mode, the subcooling degree vanishes after around 15 % refrigerant has leaked and could detect the problem in early stage while condenser fan frequency in heat pipe mode. The vapor compression mode constantly meets insufficient cooling earlier than moisture condensation despite outdoor temperature, while heat pipe mode prompts to suffer indoor air moisture condensation when outdoor temperature is lower than around −8 °C. The vapor compression mode suffers indoor air condensation constantly later than heat pipe mode, and meets insufficient cooling later except in extremely low outdoor temperature. The results can provide guidance in refrigerant leakage detection as well as elevating system reliability in fault conditions.

The westerly winds control the zonal migration of rainy season over the Tibetan Plateau

Precipitation over the Tibetan Plateau is modulated by both the South Asian summer monsoon and the mid-latitude westerly winds. Using observations and numerical simulations, this study highlights the out-of-phase relationships between the mid-latitude westerly wind speeds and the west-east migration of Tibetan Plateau rainy season. When the westerly jet shifts northward before July, the weakening of westerly winds over the Tibetan Plateau leads to a westward shift of low-level warm air center and a westward extension of moist air convergence. Consequently, rainy season advances westward. Conversely, the southward shift of westerly jet after August leads to a strengthening of westerly winds and an eastward retreat of rainy season. Numerical simulations confirm the dominant role of mid-latitude westerly winds on the rain belt migration over the Tibetan Plateau, and further indicate that the timing of the westward extension of rain belt is determined by the weakening of mid-latitude westerly winds.