Moisture Transport Mechanisms Research Articles

Atmospheric moisture budget during winter seasons in the western Himalayan region

Winter precipitation in the western Himalayas occurs under the influence of western disturbances (WDs) that move in synoptic timescale from west to east across the Himalayan region. The main objective of the study is to examine the water vapor budget during life cycles of WDs using the high-resolution global climate forecast system reanalysis data. It is found that over western Kashmir, even in climatological mean, a westerly trough is seen in moisture flux. Precipitation exceeds evaporation over most of Jammu and Kashmir, Hindukush region and the region to the west in winter seasons. Large interannual variability is noticed in all components of the moisture budget in the region. In order to understand the mechanism of moisture transport and atmospheric moisture budget over study area during the life cycle of WDs, an EOF analysis has been carried out using geopotential height at 500 hPa. The first two leading modes represent eastward moving WDs. Composite analysis of moisture budget (both atmospheric and surface) has been made using the dates from the EOF analysis. It is found that large variations in moisture transport occur during different phases of the WDs. When a cyclonic circulation is around 72°E, strong meridional moisture transport (from Arabian Sea) occurs and moisture convergence over western Himalayas enhances precipitation over the region. After the circulation moves further east, moisture convergence decreases and precipitation reduces. However, evaporation amount increases marginally due to clear sky conditions. During the life cycle of WDs, large variation in meridional transport of moisture flux is noticed as compared to zonal transport.

Surface characterization and antimicrobial properties of sodium deoxycholate-based poly(ester ether)urethane ionomer biomaterials

New sodium deoxycholate-based poly(ester ether)urethane ionomers have been obtained for the development of biomedical materials. Wettability, surface tension parameters, surface morphology, roughness, water sorption and/or desorption properties, and antimicrobial efficiency were determined for the obtained polyurethane biomembranes. Contact angle analysis evidenced that the synthesized polyurethane ionomers are hydrophilic due to orientation and amount of ionic bile salt moieties towards surface. The values of interfacial tension demonstrate biocompatible qualities for these polyurethanes. SEM microphotographs show that the resulted morphologies of polyurethane ionomers are different due to the diverse polyether co-soft segments which determine the supramolecular architecture, ionic interactions between bile salt moiety and polyether segments. AFM images evidence lamellar arrangement at the sub-micron scale and the nanophase separated morphology for these polyurethanes. The estimated moisture diffusion coefficients are dependent on a range of moisture transport mechanisms in the porous membranes and the moisture content of the polyurethanes. The monolayer sorption and average pore size values were estimated by applying BET and GAB models. GAB model could not be applied in the case of high water uptake polyurethane samples. The synthesized biocidal polyurethanes are effective at inactivation of tested bacteria: Staphylococcus aureus, Sarcina lutea, Escherichia coli, except Pseudomonas aeruginosa.

Tracking the water fingerprints of Cocos Island: a stable isotope analysis of precipitation, surface water, and groundwater

<p>The use of stable isotopes of water, both <span>δ</span><sup>2</sup>H and <span>δ</span><sup>18</sup>O has provided novel insights in hydrological studies, ecological applications, understanding climate variability, and reconstructing paleoclimate. However, information on the stable isotope composition of water in tropical marine island environments is normally scarce within the Central America Isthmus. Here, we present the first isotopic characterization of precipitation, surface water, and groundwater at Cocos Island, Costa Rica within the eastern tropical Pacific Ocean region. Our results show that the Cocos Island MWL can be described as: <span>δ</span><sup>2</sup>H=8.39·<span>δ</span><sup>18</sup>O+13.3; r<sup>2</sup>=0.98 (n=29). Dry season rainfall events ranged from -4.9 ‰ <span>δ</span><sup>18</sup>O up to -2.4 ‰ <span>δ</span><sup>18</sup>O with a mean <em>d-</em>excess of 13.2 ‰. By the beginning of May, the Intertropical Convergence Zone reaches Costa Rica resulting in a notable depletion in isotope ratios (up to -10.4 ‰ <span>δ</span><sup>18</sup>O and -76.2 ‰ <span>δ</span><sup>2</sup>H). During the wet season, <span>δ</span><sup>18</sup>O composition averaged -6.1 ‰ <span>δ</span><sup>18</sup>O and -38.5 ‰ <span>δ</span><sup>2</sup>H with a mean <em>d-</em>excess of 9.9 ‰. HYSPLIT air mass back trajectories indicate a strong influence on the origin of precipitation of two main moisture transport mechanisms, the northeasterly (January-May) and southwesterly (May-November) trade winds. Small seasonal variations were observed in the isotopic composition of surface water throughout the year with mean values ranging from -3.9 ‰ <span>δ</span><sup>18</sup>O (dry season, n=19) up to -4.8 ‰ <span>δ</span><sup>18</sup>O (wet season, n=13). Groundwater samples exhibited a similar trend with more depleted composition during the wet season (-5.2 ‰ <span>δ</span><sup>18</sup>O and -29.8 ‰ <span>δ</span><sup>2</sup>H). Overall, the marine isotopic composition measured in meteoric water at Cocos Island serves to better delineate the isotopic contribution of Pacific moisture towards the Central America Isthmus. It also provides a valuable isotopic reference to discriminate from orographic distillation and Caribbean enriched rainfall inputs in continental studies.</p><div> </div>

Salt Damage and Rising Damp Treatment in Building Structures

Salt damage can affect the service life of numerous building structures, both historical and contemporary, in a significant way. In this review, various damage mechanisms to porous building materials induced by salt action are analyzed. The importance of pretreatment investigations is discussed as well; in combination with the knowledge of salt and moisture transport mechanisms they can give useful indications regarding treatment options. The methods of salt damage treatment are assessed then, including both passive techniques based on environmental control, reduction of water transport, or conversion to less soluble salts and active procedures resulting in the removal of salts from deterioration zones. It is concluded that cellulose can still be considered as the favorite material presently used in desalination poultices but hydrophilic mineral wool can serve as its prospective alternative in future applications. Another important cause of building pathologies is the rising damp and, in this phenomenon, it is particularly severe considering the presence of salts in water. The treatment of rising damp in historic building walls is a very complex procedure and at Laboratory of Building Physics (LFC-FEUP) a wall base hygroregulated ventilation system was developed and patented.

Key drivers controlling stable isotope variations in daily precipitation of Costa Rica: Caribbean Sea versus Eastern Pacific Ocean moisture sources

Costa Rica is located on the Central American Isthmus, which receives moisture inputs directly from the Caribbean Sea and the Eastern Pacific Ocean. This location includes unique mountainous and lowland microclimates, but only limited knowledge exists about the impact of relief and regional atmospheric circulation patterns on precipitation origin, transport, and isotopic composition. Therefore, the main scope of this project is to identify the key drivers controlling stable isotope variations in daily-scale precipitation of Costa Rica. The monitoring sites comprise three strategic locations across Costa Rica: Heredia (Central Valley), Turrialba (Caribbean slope), and Caño Seco (South Pacific slope). Sporadic dry season rain is mostly related to isolated enriched events ranging from −5.8‰ to −0.9‰ δ18O. By mid-May, the Intertropical Convergence Zone reaches Costa Rica resulting in a notable depletion in isotope ratios (up to −18.5‰ δ18O). HYSPLIT air mass back trajectories indicate the strong influence on the origin and transport of precipitation of three main moisture transport mechanisms, the Caribbean Low Level Jet, the Colombian Low Level Jet, and localized convection events. Multiple linear regression models constructed based on Random Forests of surface meteorological information and atmospheric sounding profiles suggest that lifted condensation level and surface relative humidity are the main factors controlling isotopic variations. These findings diverge from the recognized ‘amount effect’ in monthly composite samples across the tropics. Understanding of stable isotope dynamics in tropical precipitation can be used to a) enhance groundwater modeling efforts in ungauged basins where scarcity of long-term monitoring data drastically limit current and future water resources management, b) improve the re-construction of paleoclimatic records in the Central American land bridge, c) calibrate and validate regional circulation models.

The effect of shrinkage cracks on the load bearing capacity of steel-fibre-reinforced roller-compacted-concrete pavements

This paper demonstrates the effect of shrinkage cracks on the static load bearing capacity and on the fatigue performance of RCC pavements reinforced with steel fibres recycled from post-consumer tyres, with the aid of a case study. A numerical method is adopted using material properties (moisture transport, free shrinkage, mechanical and fatigue) derived from experiments. It is shown that surface micro-cracks initially develop predominantly due to differential shrinkage (curling). These micro-cracks penetrate down to approximately a quarter of the slab thickness and it is shown that they reduce the ultimate load bearing and fatigue capacity of the pavement by up to 50 %. Even though shrinkage does not initially induce visible cracks, it significantly intensifies the crack opening due to traffic load by up to 500 % for a crack width of 0.5 mm. For the case studied herein, to assure the long-term performance of the pavement the allowable stress ratio should be reduced by half, to account for the effect of shrinkage distress. This study is useful because for the first time the mechanical characteristics are coupled with the moisture transport mechanism, as well as the shrinkage and fatigue characteristics. This methodology can be used for other similar materials and geometries and can lead to general conclusions regarding the importance of shrinkage distress on the design of pavements.

Experimental determination of effective moisture diffusivity during the drying of clean olive stone: Dependence of temperature, moisture content and sample thickness

Drying of clean olive stone (free of olive pulp) means a revaluation as biofuel especially used for thermal processes. This work has studied the time-dependent effective moisture diffusivity from isothermal drying experiments in a convective dryer. A new method, based on a modification of the simplified method, has been established to calculate this coefficient. A comparison between this method and the slope method has been carried out and similar results have been obtained. Modified simplified method requires fewer calculations than the slope method. The dependence between the effective moisture diffusivity, the temperature and the moisture ratio was analyzed by multiple regression analysis from a second order multivariate polynomial model and the mechanisms of moisture transport were exposed. Finally, the activation energy was analyzed and its values were shown with respect to the moisture ratio and the sample thickness.

Moisture Transport Through Sprayed Concrete Tunnel Linings

Waterproofing of permanent sprayed concrete tunnel linings with sprayed membranes in a continuous sandwich structure has been attempted since 2000 and has seen increased use in some countries. The main function of a sprayed membrane from a waterproofing perspective is to provide crack bridging and hence prevent flow of liquid water into the tunnel through cracks and imperfections in the concrete material. However, moisture can migrate through the concrete and EVA-based membrane materials by capillary and vapor diffusion mechanisms. These moisture transport mechanisms can have an influence on the degree of saturation, and may influence the pore pressures in the concrete material as well as risk of freeze–thaw damage of the concrete and membrane. The paper describes a detailed study of moisture transport material parameters, moisture condition in tunnel linings and climatic conditions tunnels in hard rock in Norway. These data have been included in a hygrothermal simulation model in the software WUFI for moisture transport to substantiate moisture transport and long-term effects on saturation of the concrete and membrane material. The findings suggest that EVA-based membranes exhibit significant water absorption and vapor transport properties although they are impermeable to liquid water flow. State-of-the-art sprayed concrete material applied with the wet mix method exhibits very low hydraulic conductivities, lower than 10−14 m/s, thus saturated conductive water flow is a very unlikely dominant transport mechanism. Moisture transport through the lining structure by capillary flow and vapor diffusion are calculated to approximately 3 cm3/m2 per day for lining thicknesses in the range of 25–35 cm and seasonal Nordic climate variations. The calculated moisture contents in the tunnel linings from the hygrothermal simulations are largely in agreement with the measured moisture contents in the tunnel linings. The findings also indicate that the concrete material exhibits a reduction of saturation on the immediate inside of the membrane. Near the location of the waterproofing membrane on either side, the concrete material exhibits degrees of capillary saturation between 85 and 95 %. Moisture content in the membrane is found to be consistently in the range of 12–17 % by weight, corresponding to a degree of saturation of 30–35 %. Possible effects of such moisture contents are lower risk of freezing degradation, higher tensile bonding strengths at the membrane interfaces, and a reduced risk of pore pressure in the concrete material.

A Comparative Study on Precipitation Climatology and Interannual Variability in the Lower Midlatitude East Asia and Central Asia

Abstract This study examines precipitation climatology and interannual variability in two regions in the lower midlatitude Asia to the east and west of the Tibetan Plateau, one located in monsoonal East Asia (the M region) and the other in semiarid central Asia (the W region). The focus is on the 5-month summer half year (May–September) for the M region and the winter half year (December–April) for the W region, corresponding to their respective rainy seasons. The main mechanism of moisture transport for the M region is the summer lower-tropospheric southerly winds, whereas the winter midtropospheric westerly circulation between 25° and 45°N is responsible for conducting moisture fluxes to the W region. It is further discovered that the winter precipitation series are positively correlated between the two regions (r = 0.47). There is also a weak cross-seasonal correlation between the winter W region precipitation and summer M region precipitation (r = 0.27). Winter westerly circulation over the W region is influenced by both the east Atlantic–western Russia and the polar–Eurasia extratropical teleconnection patterns, while El Niño–Southern Oscillation influences regional circulation patterns in both regions through teleconnections via the Indo-Pacific warm pool convection in winter and its lagged impact on the western North Pacific anticyclone over the Philippine Sea. In the meantime, responses of the regional winter circulation in the M region to the upstream westerly circulation intensity cause the correlation in winter precipitation between the two regions. Such linkages form the basis of the concurrent and cross-seasonal correlations in precipitation between the two remote regions.

The Mechanism of Moisture Transport in a Gel Cylinder

In drying of gels, the analysis of the process must encompass both heat and mass transfer aspects as well as deformation, usually very strong, of the material in the process. Deformation is almost always assumed to be linearly dependent on moisture content without considering an internal stress or pressure build-up. Since there is a great commercial interest in production of non-deformed dry gels by convective ambient pressure drying, it was interesting to investigate the behavior of such materials in drying. Convective drying would eliminate the expensive supercritical. In this work several types of gels were synthesized and dried convectively in a lab scale. Since drying induces the internal stress formation responsible for shrinkage and cracking, great care was taken to measure deformation and internal pressure development in gel during drying. Cylindrical gel samples 35 mm in diameter were dried convectively in air at 30, 40, and 50 °C. The hydrogels were made of PVP, agar-agar, and silica. Different types of behavior of the gels during drying was observed: almost uniform deformation in the case of PVP, case-hardening for agar-agar gels, and cracking for silica hydrogels. This behavior directly results from different mechanical properties of the investigated gels. It was also observed that the internal pressure changes from initially overpressure to underpressure in the course of drying which is also a result of internal stress build up. The experimental data may be used for validation of mechanical models of drying of non-linear visco-elastic solids.

Analysis of Moisture Transfer During the Drying of Clay Tiles with Particular Reference to an Estimation of the Time-Dependent Effective Diffusivity

The description of the drying process was reduced to the establishment of a series of theoretical and empirical drying models. The complex processes of simultaneous moisture and heat transfer, which are often nonstationary, and the distinct nature and properties of the material to be dried further complicate the description of the drying process. Three theories—diffusion theory, capillary flow theory, and evaporation–condensation theory—have won general recognition for the explanation of moisture transfer in porous media. The mechanisms of moisture movement during drying in the constant and especially in the falling drying period are rather complex and, hitherto, there have been no generally accepted explanations that could identify the exact transition between possible drying mechanisms, such as liquid movement due to capillary forces, liquid diffusion due to concentration gradients, liquid and vapor flow due to differences in total pressure, vapor diffusion due to difference in vapor concentration, vapor diffusion due to partial vapor pressure gradients, Knudsen diffusion, thermodiffusion, and the evaporation–condensation mechanism. The goal of this study was to find a way to better understand the different drying mechanisms, to identify the exact transition between them, and to estimate the time-dependent effective diffusivity. The results presented in this article confirmed that the effective diffusivity represents an overall mass transport property of moisture that includes all possible moisture transport mechanisms that are simultaneously controlling the moisture migration process in a material during drying. The experimental investigations were performed on clay tiles in a laboratory recirculation dryer, for which the drying parameters (humidity, temperature, and velocity) could be programmed, controlled, and monitored during drying.

Uniform Model for Moisture Transport in Porous Materials and Its Application to Concrete at Selected Chinese Regions

The present study investigates the mechanisms of moisture transport in porous materials. For partially saturated porous materials, moisture transport relies on both the Darcian flow by capillary pressure gradient and the Fickian flow by gas concentration gradient. Taking into account the capillary curves that are associated intimately with the pore structure and play crucial roles on both drying and wetting processes, a uniform model that only depends on one variable, the saturation degree, is established. The isothermal adsorption/desorption method and the Kelvin equation are used to evaluate the capillary curve that obeys the van Genuchten form equation. The established model is applied to characterize the moisture distribution in four (near) coastal regions of China (Guangzhou, Hangzhou, Jinan, and Shenyan). Wetting time is shown to be a dominant factor influencing the stable saturation degree and the influence depth.

Modeling Hydroionic Transport in Cement-Based Porous Materials Under Drying-Wetting Actions

This paper investigates the hydroionic transport processes at the near surface of cement-based porous materials under external drying-wetting (D-W) actions. A basic multiphase model is retained and reviewed critically for moisture transport under D-W actions. The multiphase model fails to account for the substantial difference between moisture diffusivities during drying and wetting. The multiphase model is adapted for moisture transport under D-W actions through the respective mechanisms of moisture transport during drying and wetting. Together with the associated ionic transport, a global hydroionic model is established and the corresponding numerical scheme is developed to solve the near surface transport problem. Then, systematic experiments are performed on two concretes with high and low porosities for transport properties and hydroionic transport under D-W actions with pure water and salt solution. Experimental data validate the global model, while some fundamental aspects of hydroionic modeling are discussed.

Mass Transfer in Irregularly-Shaped Solid: An Exact Solution Using the Galerkin-Based Integral Method

This paper presents a theoretical investigation of the mass transfer during the drying of solids of revolution with arbitrary shape. A two-dimensional mathematical model by assuming the liquid diffusion to be the sole mechanism of moisture transport, constant thermophysical properties and convective boundary condition at the surface of the solid is presented. The resulting equation is solved analytically by using the Galerkin-based integral method. Results of the mean moisture content and moisture content distribution within the porous solid are present and analyzed during the process, for different Biot number and aspect ratio. We conclude that solid drying rate is affected by Biot number and area/volume relationships, and which drying process is faster in sharp areas and closed to surface of the solid.

Effects of Irrigation Water Quality and Drip Tape Arrangement on Soil Salinity, Soil Moisture Distribution, and Cotton Yield (Gossypium hirsutum L.) Under Mulched Drip Irrigation in Xinjiang, China

More and more attention is being focused on saline water utilization in irrigation due to the shortage of fresh water to agriculture in many regions. For purpose of reducing the risks of using of saline water for irrigation, the mechanism of soil moisture and salinity distribution and transport should be well understood for developing optimum management strategies. In this paper, field experiments were carried out at Junggar Basin, China, to study the effects of drip irrigation water quality and drip tape arrangement on distribution of soil salinity and soil moisture. Six treatments were designed, including two drip tape arrangement modes and three irrigation water concentration levels (0.24, 4.68, and 7.42 dS m−1). Results showed that, soil moisture content (SMC) directly beneath the drip tape in all treatments kept a relatively high value about 18% before boll opening stage; the SMC in the narrow strip in single tape arrangement (Ms) plot was obviously lower than that in the double tapes arrangement (Md) plot, indicating that less sufficient water was supplied under the same condition of irrigation depth, but there was no significant reduction in yield. Mulching had not significant influence on salt accumulation but the drip tape arrangement, under the same condition of irrigation water depth and quality, compared with Md, Ms reduced salt accumulation in root zone and brought about relatively high cotton yield.

Recent changes in the circulation parameters and their association with Indian summer monsoon rainfall

The phenomena of Earth's climate system and its associated rainfall are mainly driven by the changes in various circulation parameters embedded with the local atmospheric instability. An attempt has been made in the present study to examine the recent changes in four selected regional circulation parameters viz., zonal wind at 200hPa level over Tibetan Anticyclone region (TAU200), zonal wind at 100hPa over peninsular India i.e. Tropical Easterly Jet (TEJU100), meridional wind (Somali Jet) at 850hPa over Somali Coast (SJV850) and meridional wind at 850hPa over Arabian Sea (ASV850) using NCEP/NCAR reanalysis dataset during the period 1949–2008. The influences of these circulation parameters in the Indian summer monsoon rainfall (ISMR) have also been brought out. ASV850 and TEJU100 show decreasing tendency which in turn leads to the weakening of the moisture transport mechanism over the Indian sub-continent during the monsoon season whereas the other parameters TAU200 and SJV850 show increasing tendency. TEJU100 shows highly significant decreasing trends throughout the monsoon months and season with a very strong positive relationship with ISMR. The intensity of the TAU200 on monthly scale seems to have less impact as compared to the other circulation parameters on ISMR during the warming scenario though it plays a vital role in modulating the general atmospheric circulation.

Drying process in Norway spruce wood exposed to infrared radiation

The drying process of Norway spruce (Picea abies [L.] Karst) wood exposed to infrared heat radiation was studied by measuring the moisture profiles of the wood samples at controlled temperature during drying. The thermal treatment was executed in a purpose-made industrial pilot-plant containing the heat radiators covered by infrared (IR) transmition filters. The moisture content of the samples was detected at certain stages of the process. Based on the results of exposing the samples to IR radiation for 15, 25, 35, and 45 hours, the drying mechanism of wood is discussed. The moisture transport mechanism was explained by a semipermeable membrane process considering the moisture content as a dilute aqueous solution. If the semipermeable cell wall allows only the passage of water but not that of solute molecules, water diffusing from the region of higher (center) to lower (periphery) water content produces osmotic pressure difference between the two sides of the cell walls. The importance of this osmosis was considered in the approach of moisture migration.

Hybrid mixture theory based moisture transport and stress development in corn kernels during drying: Validation and simulation results

The moisture transport and stress development mechanisms were elucidated for corn kernels using numerical solution of three-scale fluid transport equation. The 3D kernel structure was captured using micro-CT scanning and imported into finite elements package. The experimental drying profiles were predicted with reasonable accuracy (R2=0.88–0.99 and CV=3.5–9.5%). During simulations, the region with highest moisture content was observed to be away from the geometric center covering parts of soft-endosperm and germ. The high moisture flux was observed under the pericarp, in soft-endosperm toward top and in region connecting soft-endosperm and germ. The germ due to its lower moisture diffusivity in comparison to hard and soft endosperms, retained higher moisture and exhibited lower moisture flux. These observations agreed with previous magnetic resonance imaging based studies. Intermittent drying simulations indicated that fan on/off strategies with suitable time step-size would be a viable option for drying corn with lower stress-cracking and additional energy savings.

Drying Kinetics and Antioxidant Phytochemicals Retention of Salak Fruit under Different Drying and Pretreatment Conditions

Kinetics of hot air drying and heat pump drying were studied by performing various drying trials on salak slices. Isothermal drying trials were conducted in hot air drying and heat pump drying at a temperature range of 40–90°C and 26–37°C, respectively. Intermittent drying trials were carried out in heat pump drying with two different modes: periodic heat air flow supply and step-up air temperature. It was observed that the effects of relative humidity and air velocity on drying rate were significant when moisture content in salak slices was high, whereas the effects of temperature prevailed when the moisture content was low. As such, it was proposed that drying conditions should be manipulated according to the moisture transport mechanisms at different stages of drying in order to optimize the intermittent drying and improve the product quality. Generally, loss of ascorbic acid during drying was attributed to thermal degradation and enzymatic oxidation, whereas the loss of phenolic compounds was mainly due to thermal degradation. Experimental results showed that heat pump drying with low-temperature dehumidified air not only enhanced the drying kinetics but produced a stable final product. Heat pump–dried samples retained a high concentration of ascorbic acid and total phenolic compounds when an appropriate drying mode was selected.

Study of the soil–atmosphere moisture exchanges through convective drying tests in non‐isothermal conditions

AbstractThis paper deals with the moisture exchanges occurring between soils and the surrounding atmosphere. Convective drying tests are performed on Awans silts at different drying temperatures and air relative humidities in order to reproduce the natural drying conditions. The experiments improve the understanding of the vapour transfers kinetics between the soil samples and the atmosphere. The experimental results are analysed assuming that the transfers take place in a boundary layer existing at the surface of the porous medium. The influence of the thermal conditions on the evaporation is also taken into account. In our model, coupled vapour and energy exchanges are controlled by mass and heat transfer coefficients characterizing the boundary layer. These coefficients are determined from the drying experiments. The modelling of the drying tests in non‐isothermal conditions is performed in order to validate the formulation of the vapour and heat exchanges. The numerical results present a good agreement with the kinetic of the materials desaturation determined during the tests. The analysis of the moisture transport mechanisms into the sample and at the boundary shows that at the beginning of the test, the drying is first achieved by the transport of moisture in its liquid form and its evaporation at the sample outer boundary in contact with the atmosphere. In a second step, vapour diffusion becomes predominant into the sample and it corresponds to the most important decrease of relative humidity. Copyright © 2009 John Wiley & Sons, Ltd.