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Water Vapour (water + vapour)
Terms modified by Water Vapour Selected AbstractsSpatial interpolation of GPS integrated water vapour measurements made in the Swiss AlpsMETEOROLOGICAL APPLICATIONS, Issue 1 2007June Morland Abstract The 31 stations in the Swiss GPS network are located at altitudes between 330 and 3584 m and have provided hourly Integrated Water Vapour (IWV) measurements since November 2000. A correction based on an exponential relationship is proposed for the decrease in IWV with altitude. The scale height depends on the ratio of IWV measured at Jungfraujoch (3584 m) to that measured at Payerne (498 m). An additional coefficient, dependent on the east-west and north-south spatial differences in the IWV, improves the fit to the data. The IWV at heights between 750 and 3500 m was estimated from GPS measurements at Payerne and compared with the Payerne radiosounding. The altitude correction introduced an additional bias of 0.2 to 0.4 mm between GPS and radiosonde. The IWV was normalized to 500 m and the increases and decreases due to the passage of a series of frontal systems between 11 and 14 January 2004 were mapped. A four-year climatology of IWV normalized to 500 m showed that the Alpine stations are more moist in spring, summer and autumn than the stations in the Swiss plains to the north of the Alps. This was attributed to more moist Mediterranean air being blocked by the Alps. Copyright © 2007 Royal Meteorological Society [source] The assimilation of SSM/I and TMI rainfall rates in the ECMWF 4D-Var systemTHE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 606 2005Jean-françois Mahfouf Abstract A recent version of the European Centre for Medium-Range Weather Forecasts four-dimensional variational (4D-Var) assimilation system (40 km horizontal resolution with a 12-hour window) is used to examine the comparative impact of including satellite-derived rainfall rates from SSM/I and TMI radiometers within the tropics. The methodology is similar to the one proposed by Marécal and Mahfouf (2002) where Total Column Water Vapour (TCWV) retrievals in rainy areas from a simplified 1D-Var assimilation are introduced in the 4D-Var system. An improved methodology for the estimation of rain rate retrieval errors proposed by Bauer et al. (2002) is used. Three one-month experiments are undertaken: a control run (no rain rate assimilation), a TMI run (assimilation of TMI-derived rain rates) and a SSM/I run (assimilation of SSM/I-derived rain rates). The corrections of TCWV in rainy areas introduced in the 4D-Var are very similar between SSM/I and TMI because they are dominated by the ,no rain' information. The impact of TMI and SSM/I assimilations is positive on forecast scores, both in the extratropics and in the tropics. Results from the SSM/I run show a larger positive impact which tends to demonstrate the benefit of the increased number of data from the SSM/I with respect to TMI. Copyright © 2005 Royal Meteorological Society. [source] Reversible Collapse of Brushlike Macromolecules in Ethanol and Water Vapours as Revealed by Real-Time Scanning Force MicroscopyCHEMISTRY - A EUROPEAN JOURNAL, Issue 18 2004Marat O. Gallyamov Dr. Abstract Environment-controlled scanning force microscopy allowed us to study adsorption and desorption of single poly(methacrylate)- graft -poly(n -butyl acrylate) brush molecules on mica in real time. The molecules transform reversibly from a two-dimensional, extended wormlike state to a compact globular state. The dynamics of the conformational transition was sufficiently slow in order to allow its observation by scanning force microscope in real time. The reversible transformation is effected by coadsorption of water or ethanol, the latter introduces the collapse. Adsorbing ethanol and water from the vapour atmosphere results in a change of the surface properties of mica, either favouring adsorption or desorption of the graft polymer. When the extended, tightly adsorbed poly(n -butyl acrylate) brush molecules are exposed to ethanol vapour, the macromolecules swell and contract to form compact globules. Exchanging the ethanol vapour to a humid atmosphere caused the molecules to extend again to a wormlike two-dimensional conformation. Coexistence of collapsed and extended strands within the same molecule indicates a single-molecule first-order transition in agreement with observations on Langmuir films previously reported. [source] Measurement of atmospheric water vapour on the ground's surface by radio wavesHYDROLOGICAL PROCESSES, Issue 11 2001Tokuo Kishii Abstract Water vapour in the atmosphere and various meteorological phenomena are essential to the understanding of the mechanism of the water cycle. However, it is very difficult to observe water vapour in the atmosphere because the quantities are usually observed at a single point not over long intervals or in a specific plane or volume. Accordingly, the use of radio waves is considered to be necessary to observe water vapour. Radio waves can be transmitted over long intervals and across large areas, and generally speaking, the characteristics of radio waves change due to material in the atmosphere, especially water vapour. Usually absorption is used to observe the quantity of water vapour. But the relationship between absorption and the quantity of water vapour is not linear, so we try to utilize the phase difference between two radio waves as an alternative method. First, the relationship between the phase delay and the water vapour was induced by a physical equation and the resulting phase delay was found to be proportional to the quantity of water vapour. Furthermore, the phase difference between two separate points was observed by use of two radio waves in the field, specifically 84 GHz and 245 GHz. For reference and comparison, water vapour density in the atmosphere was simultaneously observed by meteorological observation. As a result, the density of the water vapour was found to be proportional to the phase difference between the two radio waves. The result also shows that this method is able to measure the diurnal changes in water vapour density in each season. Copyright © 2001 John Wiley & Sons, Ltd. [source] Tests for the Use of La2Mo2O9 -based Oxides as Multipurpose SOFC Core MaterialsFUEL CELLS, Issue 3 2010J. Jacquens Abstract The mixed ionic,electronic conductivity under dilute hydrogen, the stability and the catalytic activity under propane:air type mixtures of a series of LAMOX oxide-ion conductors have been studied. The effect of exposure to dilute hydrogen on the conductivity of the ,-La2(Mo2,,,yWy)O9 series at 600,°C depends on tungsten content: almost negligible for the highest (y,=,1.4), it is important for La2Mo2O9 (y,=,0). In propane:air, all tested LAMOX electrolytes are stable at 600,700,°C, but get reduced when water vapour is present. La2Mo2O9 is the best oxidation catalyst of the series, with an activity comparable to that of nickel. The catalytic activity of other tested LAMOX compounds is much lower, (La1.9Y0.1)Mo2O9 showing a deactivation phenomenon. These results suggest that depending on composition, La2(Mo2,,,yWy)O9 compounds could be either electrolytes in single-chamber SOFC and dual-chamber micro-SOFC (y,=,1.4) or anode materials in dual-chamber SOFC (low y) or oxidation catalysts in SOFCs operating with propane (y,=,0). [source] Dehydration tolerance and water vapour absorption in two species of soil-dwelling Collembola by accumulation of sugars and polyolsFUNCTIONAL ECOLOGY, Issue 5 2001M. Holmstrup Summary 1,Physiological and biochemical responses to desiccation were studied in two species of hygrophilic Collembola, Folsomia fimetaria L. and Protaphorura armata Tullberg. The temporal changes in water content, body fluid osmotic pressure, and accumulation of sugars and polyols during desiccation stress, equivalent to severe soil drought are reported. 2,Both species initially lost about 50% of their initial content of osmotically active water. Within 7 days F. fimetaria had re-established their preliminary water content by absorbing water vapour from the atmosphere. Protaphorura armata also significantly increased their water content over the following 10 days. 3,Both species were able to resume their hyperosmotic status relative to the desiccating environment they were placed in. The accumulation of myo-inositol and two other unidentified compounds (F. fimetaria) and trehalose (P. armata) made an important contribution to this phenomenon. 4,These results suggest that water vapour absorption by accumulation of sugars and polyols may be widespread in soil-dwelling Collembola. [source] Estimation of mean residence times of subsurface waters using seasonal variation in deuterium excess in a small headwater catchment in JapanHYDROLOGICAL PROCESSES, Issue 3 2007Naoki Kabeya Abstract We measured deuterium excess (d = ,D , 8,18O) in throughfall, groundwater, soil water, spring water, and stream water for 3 years in a small headwater catchment (Matsuzawa, 0·68 ha) in the Kiryu Experimental Watershed in Japan. The d value represents a kinetic effect produced when water evaporates. The d value of the throughfall showed a sinusoidal change (amplitude: 6·9, relative to Vienna standard mean ocean water (V-SMOW)) derived from seasonal changes in the source of water vapour. The amplitude of this sinusoidal change was attenuated to 1·3,6·9, V-SMOW in soil water, groundwater, spring water, and stream water. It is thought that these attenuations derive from hydrodynamic transport processes in the subsurface and mixing processes at an outflow point (stream or spring) or a well. The mean residence time (MRT) of water was estimated from d value variations using an exponential-piston flow model and a dispersion model. MRTs for soil water were 0,5 months and were not necessarily proportional to the depth. This may imply the existence of bypass flow in the soil. Groundwater in the hillslope zone had short residence times, similar to those of the soil water. For groundwater in the saturated zone near the spring outflow point, the MRTs differed between shallow and deeper groundwater; shallow groundwater had a shorter residence time (5,8 months) than deeper groundwater (more than 9 months). The MRT of stream water (8,9 months) was between that of shallow groundwater near the spring and deeper groundwater near the spring. The seasonal variation in the d value of precipitation arises from changes in isotopic water vapour composition associated with seasonal activity of the Asian monsoon mechanism. The d value is probably an effective tracer for estimating the MRT of subsurface water not only in Japan, but also in other East Asian countries influenced by the Asian monsoon. Copyright © 2006 John Wiley & Sons, Ltd. [source] The canopy conductance of a boreal aspen forest, Prince Albert National Park, CanadaHYDROLOGICAL PROCESSES, Issue 9 2004P. D. Blanken Abstract Annual fluxes of canopy-level heat, water vapour and carbon dioxide were measured using eddy covariance both above the aspen overstory (Populus tremuloides Michx.) and hazelnut understory (Corylus cornuta Marsh.) of a boreal aspen forest (53·629 °N 106·200 °W). Partitioning of the fluxes between overstory and understory components allowed the calculation of canopy conductance to water vapour for both species. On a seasonal basis, the canopy conductance of the aspen accounted for 70% of the surface conductance, with the latter a strong function of the forest's leaf area index. On a half-hour basis, the canopy conductance of both species decreased non-linearly as the leaf-surface saturation deficits increased, and was best parameterized and showed similar sensitivities to a modified form of the Ball,Berry,Woodrow index, where relative humidity was replaced with the reciprocal of the saturation deficit. The negative feedback between the forest evaporation and the saturation deficit in the convective boundary layer varied from weak when the forest was at full leaf to strong when the forest was developing or loosing leaves. The coupling between the air at the leaf surface and the convective boundary layer also varied seasonally, with coupling decreasing with increasing leaf area. Compared with coniferous boreal forests, the seasonal changes in leaf area had a unique impact on vegetation,atmosphere interactions. Copyright © 2004 John Wiley & Sons, Ltd. [source] Measurement of atmospheric water vapour on the ground's surface by radio wavesHYDROLOGICAL PROCESSES, Issue 11 2001Tokuo Kishii Abstract Water vapour in the atmosphere and various meteorological phenomena are essential to the understanding of the mechanism of the water cycle. However, it is very difficult to observe water vapour in the atmosphere because the quantities are usually observed at a single point not over long intervals or in a specific plane or volume. Accordingly, the use of radio waves is considered to be necessary to observe water vapour. Radio waves can be transmitted over long intervals and across large areas, and generally speaking, the characteristics of radio waves change due to material in the atmosphere, especially water vapour. Usually absorption is used to observe the quantity of water vapour. But the relationship between absorption and the quantity of water vapour is not linear, so we try to utilize the phase difference between two radio waves as an alternative method. First, the relationship between the phase delay and the water vapour was induced by a physical equation and the resulting phase delay was found to be proportional to the quantity of water vapour. Furthermore, the phase difference between two separate points was observed by use of two radio waves in the field, specifically 84 GHz and 245 GHz. For reference and comparison, water vapour density in the atmosphere was simultaneously observed by meteorological observation. As a result, the density of the water vapour was found to be proportional to the phase difference between the two radio waves. The result also shows that this method is able to measure the diurnal changes in water vapour density in each season. Copyright © 2001 John Wiley & Sons, Ltd. [source] Precipitation characteristics of the Eurasian Arctic drainage systemINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 11 2003Mark C. Serreze Abstract This study examines characteristics of precipitation over the major watersheds of the Eurasian Arctic drainage system over the period 1960,92. In addition to the Ob, Yenisey and Lena (the three largest drainage systems), we examine the combined Kolyma,Indigirka in eastern Eurasia. Each basin exhibits approximately symmetric mean annual cycles of monthly total precipitation and daily event size, with winter minima and July maxima. These are strikingly similar to the annual cycles of total column water vapour (precipitable water), which fundamentally reflects the control on saturation vapour pressure by temperature. Effective precipitation mechanisms exist in all seasons. However, because of the long distance from strong moisture sources (continentality), precipitation tends to follow the seasonality in column water vapour. An effective contrast is presented for the Iceland sector. Here, the annual cycle of precipitation is tied not to the seasonality in column water vapour, but to the stronger precipitation-generating mechanisms in winter. Hence, the annual cycles of precipitation and column water vapour in this region oppose each other. Mean winter precipitation over the Eurasian watersheds is primarily driven by a modest convergence of water vapour. Whereas precipitation peaks in summer, the mean flux convergence exhibits a general minimum (negative in the Ob). Summer precipitation is hence primarily associated with surface evaporation. A strong role of convection is supported from consideration of static stability, the fairly weak spatial organization of precipitation totals and results from prior studies. On daily time scales, the largest basin-averaged precipitation events, for both summer and winter, are allied with synoptic-scale forcing. This is seen in relationships with cyclone frequency, and patterns of 500 hPa height, vertical motion and the 700 hPa vapour flux. The relative frequency of four 500 hPa synoptic types captures the basic time series structures of precipitation. Copyright © 2003 Royal Meteorological Society [source] Human synthetic sebum formulation and stability under conditions of use and storageINTERNATIONAL JOURNAL OF COSMETIC SCIENCE, Issue 1 2009P. W. Wertz Synopsis The human skin surface and hair are generally coated with a thin film of liquid phase sebaceous lipids. This surface lipid film contributes to the cosmetic properties of the skin. Synthetic sebum has been used for studies on properties of skin and hair. However, there has been no standardized formulation of synthetic sebum and many of the synthetic sebum formulations that have been used do not closely resemble actual sebum. In this study, a formulation for a standardized and inexpensive synthetic sebum is proposed, and the chemical stability of this lipid mixture is demonstrated under conditions of use and storage. The proposed synthetic sebum consists of 17% fatty acid, 44.7% triglyceride, 25% wax monoester (jojoba oil) and 12.4% squalene. This lipid mixture takes up approximately 6% of its weight in water when equilibrated in an atmosphere saturated with water vapour. It is stable on exposure to the atmosphere at 32°C for at least 48 h, and it is also stable on storage at 4 or ,20°C, either dry or in chloroform : methanol solution for at least 6 months. This synthetic sebum could be useful in studies on cosmetic properties of the skin surface or hair, on penetration of chemicals into the skin or in development of standardized tests of laundry detergent performance. Résumé La surface de la peau et les poils de l'être humain sont généralement enduits d'un mince film de lipides sébacés en phase liquide. Ce film lipidique de surface contribue aux propriétés esthétiques de la peau. Bien que du sébum synthétique ait été employéà des fins d'études sur les propriétés de la peau et des poils, il n'en éxiste pas de formulation standardisée. Plusieurs des formulations utilisées ne ressemblent pas au sébum naturel. La présente étude propose une formulation standardisée et peu coûteuse d'un sébum synthétique; elle vise aussi à démontrer sa stabilité chimique dans des conditions d'utilization et de stockage. Le sébum synthétique tel que proposé est composé de 17% d'acides gras, de 44.7% de triglycérides, de 25% d'un mono ester de cire (huile de jojoba) et de 12.4% de squalène. Ce mélange lipidique prend environ 6% de son poids dans l'eau lorsqu'il est équilibré dans une atmoshpère saturée en vapeur d'eau. Le mélange demeure stable pendant au moins 48 heures lorsque éxposéà une atmoshpère de 32o. Il le demeure également dans des conditions de stockage de 4oà,20oà sec ou en solution de chloroforme:méthanol pendant au moins 6 mois. Ce sébum synthétique pourrait être utile àétudier les propriétés esthétiques de la surface de la peau et des poils ou de la pénétration cutanée de produits chimiques. Il pourrait aussi servir àélaborer des tests standardisés de rendement des détergents de lessive. [source] Influence of high rates of supplemental cooled EGR on NOx and PM emissions of an automotive HSDI diesel engine using an LP EGR loopINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 15 2008A. Maiboom Abstract Previous experimental studies on diesel engine have demonstrated the potential of exhaust gas recirculation (EGR) as an in-cylinder NOx control method. Although an increase in EGR at constant boost pressure (substitution EGR) is accompanied with an increase in particulate matter (PM) emissions in the conventional diesel high-temperature combustion (HTC), the recirculation of exhaust gases supplementary to air inlet gas (supplemental EGR) by increasing the boost pressure has been suggested as a way to reduce NOx emissions while limiting the negative impact of EGR on PM emissions. In the present work, a low-pressure (LP) EGR loop is implemented on a standard 2.0 l automotive high-speed direct injection (HSDI) turbocharged diesel engine to study the influence of high rates of supplemental cooled EGR on NOx and PM emissions. Contrary to initial high-pressure (HP) EGR loop, the gas flow through the turbine is unchanged while varying the EGR rate. Thus, by closing the variable geometry turbine (VGT) vanes, higher boost pressure can be reached, allowing the use of high rates of supplemental EGR. Furthermore, recirculated exhaust gases are cooled under 50°C and water vapour is condensed and taken off from the recirculated gases. An increase in the boost pressure at a given inlet temperature and dilution ratio (DR) results in most cases an increase in NOx emissions and a decrease in PM emissions. The result of NOx,PM trade-off, while varying the EGR rate at fixed inlet temperature and boost pressure depends on the operating point: it deteriorates at low load conditions, but improves at higher loads. Further improvement can be obtained by increasing the injection pressure. A decrease by approximately 50% of NOx emissions while maintaining PM emission level, and brake specific fuel consumption can be obtained with supplemental cooled EGR owing to an LP EGR loop, compared with the initial engine configuration (HP moderately cooled EGR). Copyright © 2008 John Wiley & Sons, Ltd. [source] Structural changes and shrinkage of potato during fryingINTERNATIONAL JOURNAL OF FOOD SCIENCE & TECHNOLOGY, Issue 1 2001Rui M. Costa Summary Light microscopy was used to study changes in cell size, blister formation and crust evolution during potato frying. Frying experiments with both French fries and crisps of different thickness (1,5 mm) were performed at temperatures of 140 and 180 °C. Thickness, volume and density changes were also measured. The formation of crust in French fries starts after the potato surface reached approximately 103 °C, and then the crust thickness increased linearly with the square root of frying time, this increase being faster at 180 °C. The potato volume decreased during frying, although in the late stages the volume may increase because of oil uptake and cell separation caused by entrapped water vapour. Shrinkage was adequately described by the Weibull model with a residual value, with shrinkage rate increasing with temperature and decreasing with potato thickness. The residual volume was not affected by temperature (65% for French fries and 59,30 for crisps, depending on thickness). Volume appeared to decrease mainly as the result of water loss, except for very low water content, and thus potato density changes were very small. [source] Seasonal and diurnal variations of total attenuation measured with the ITALSAT satellite at Spino d'Adda at 18.7, 39.6 and 49.5 GHzINTERNATIONAL JOURNAL OF SATELLITE COMMUNICATIONS AND NETWORKING, Issue 4 2004Carlo Riva Abstract The ITALSAT satellite experiment started in January 1991 and ended in January 2001, permitting an extensive program of propagation measurements at 18.7, 39.6 and 49.5 GHz. In these frequency bands, up- and down-links experience severe signal attenuation due to meteorological effects such as those due to gas (oxygen and water vapour), clouds, turbulence and, especially, rain. The propagation measurement campaigns aim mainly at assessing and at modelling the appropriate fade margin compensating propagation attenuation in the design of satellite communication systems. This margin depends significantly on the season and on the time of the day, due to variations of meteorological conditions. This paper reports the results obtained from copolar signal measurements carried out at the Earth station of Spino d'Adda, near Milano (North Italy), at the three frequencies during 7 years (from 1994 to 2000). The measured cumulative distribution functions of total attenuation are compared to ITU-R models' prediction. Moreover the statistics conditioned to single months of the year, seasons and 4 h contiguous periods of the day are also shown. These statistics can be useful for telecommunication systems whose service quality and design must be matched to the season of the year or the time of the day. Copyright © 2004 John Wiley & Sons, Ltd. [source] Precipitable water vapour estimation on the basis of sky temperatures measured by a single-pixel IR detector and screen temperatures under clear skiesMETEOROLOGICAL APPLICATIONS, Issue 3 2010A. Maghrabi Abstract Precipitable water vapour (PWV) is an important component of the atmosphere, but remains difficult to measure with adequate spatial and temporal resolution under all weather conditions. Over the last four decades several techniques and methods have been developed to measure PWV more accurately, but each carries limitations preventing its widespread use. This paper presents preliminary results of a simple method for inferring PWV from the air temperature and infrared (IR) sky temperature under clear skies. Sky temperatures are measured using a broadband, single-pixel IR radiometer. A parametric model of the physical relationship between these three quantities was created using PWV data derived from a GPS receiver. By inverting the model, PWV estimates can be obtained from new temperature measurements. The measurements were taken between October 2002 and July 2004 in a coastal region of South Australia. The method was found to predict PWV quite accurately, with a mean bias error (MBE) of only , 0.009 mm and a root mean square error (RMSE) of 2.311 mm. The model was also compared to a set of 120 radiosonde-derived PWV values, resulting in a MBE and RMSE of 0.262 and 2.601 mm respectively. These preliminary results show that the clear sky PWV can be estimated accurately from sky temperatures obtained using a simple IR detector. Future work will extend the method to different sky and weather conditions. Copyright © 2009 Royal Meteorological Society [source] The application of AVHRR data for the detection of volcanic ash in a Volcanic Ash Advisory CentreMETEOROLOGICAL APPLICATIONS, Issue 4 2003S. C. Watkin A volcanic ash detection product using AVHRR data has been developed for use in the London Volcanic Ash Advisory Centre, operated by forecasters at the Met Office. The product is an image that shows the brightness temperature difference between two infrared channels, which can be used to discriminate between clouds containing volcanic ash particles and those containing water droplets or ice crystals. Factors such as water vapour, water droplet and ice crystal content, opacity, cloud top temperature, ash particle size, surface emissivity properties and instrumental effects all have an effect on the spectral signal represented in the image. AVHRR imagery has been used to study the volcanic clouds ejected from eruptions of Mount Etna (Italy) in July 2001, Hekla (Iceland) in February 2000 and Mount Spurr (USA) in September 1992 to demonstrate the application of this product during volcanic events. The volcanic ash detection product provides essential information that can help forecasters locate volcanic ash and give appropriate guidance through advisory statements to the aviation industry and thus help avoid dangerous and expensive encounters between aircraft and volcanic ash. Copyright © 2003 Royal Meteorological Society. [source] Spectrum of hot water in the 4750,13 000 cm,1 wavenumber range (0.769,2.1 ,m)MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 3 2008Nikolai F. Zobov ABSTRACT The high resolution laboratory spectrum of hot water vapour has been recorded in the 500,13 000 cm,1 wavenumber range and we report on the analysis of the 4750,13 000 cm,1 (0.769,2.1 ,m) portion. The emission spectrum was recorded using an oxy-acetylene welding torch and a Fourier transform spectrometer. Line assignments in the laboratory spectrum as well as in an absorption spectrum of a sunspot umbra were made with the help of the BT2 line-list. Our torch spectrum is the first laboratory observation of the 9300 Å,steam bands' seen in M-stars and brown dwarfs. [source] NH3 and NO2 fluxes between beech trees and the atmosphere , correlation with climatic and physiological parametersNEW PHYTOLOGIST, Issue 3 2000ARTHUR GESSLER The dynamic-chamber technique was used to investigate the correlation between NH3 and NO2 fluxes and different climatic and physiological parameters: air temperature; relative air humidity; photosynthetic photon fluence rate; NH3 and NO2 concentrations; transpiration rate; leaf conductance for water vapour; and photosynthetic activity. The experiments were performed with twigs from the sun crown of mature beech trees (Fagus sylvatica) at a field site (Höglwald, Germany), and with 12-wk-old beech seedlings under controlled conditions. Both sets of experiments showed that NO2 and NH3 fluxes depended linearly on NO2 and NH3 concentration, respectively, in the concentration ranges representative for the field site studied, and on water-vapour conductance as a measure for stomatal aperture. The NO2 compensation point determined in the field studies (the atmospheric NO2 concentration with no net NO2 flux) was 1.8,1.9 nmol mol,1. The NH3 compensation point varied between 3.3 and 3.5 nmol mol,1 in the field experiments, and was 3.0 nmol mol,1 in the experiments under controlled conditions. The climatic factors T and PPFR were found to influence both NO2 and NH3 fluxes indirectly, by changing stomatal conductance. Whilst NO2 flux showed a response to changing relative humidity that could be explained by altered stomatal conductance, increased NH3 flux with increasing relative humidity (>50%) depended on other factors. The exchange of NO2 between above-ground parts of beech trees and the atmosphere could be explained exclusively by uptake or emission of NO2 through the stomata, as indicated by the quotient between measured and predicted NO2 conductance of approx. 1 under all environmental conditions examined. Neither internal mesophyll resistances nor additional sinks could be observed for adult trees or for beech seedlings. By contrast, the patterns of NH3 flux could not be explained by an exclusive exchange of NH3 through the stomata. Deposition into additional sinks on the leaf surface, as indicated by an increase in the quotient between measured and predicted NH3 conductance, gained importance in high air humidity, when the stomata were closed or nearly closed and/or when atmospheric NH3 concentrations were high. Although patterns of NH3 gas exchange did not differ between different months or years at high NH3 concentrations (c. 140 nmol mol,1), it must be assumed that emission or deposition fluxes at low ambient NH3 concentration (0.8 and 4.5 nmol mol,1) might vary significantly with time because of variation in the NH3 compensation point. [source] A simple model for the interaction between water vapour and oxygen transmission in multilayer barrier materials intended for food packaging applicationsPACKAGING TECHNOLOGY AND SCIENCE, Issue 4 2008Marianne Jakobsen Abstract The low oxygen permeability of the ethylene-vinyl alcohol copolymer, EVOH, is outstanding, but is also known to be very sensitive to moisture uptake and cannot be used as a monolayer packaging material. In this paper, theory is presented in order to calculate the average water activity of the EVOH layer at steady state and the corresponding oxygen barrier for different multilayer structures using various polymer types and layer thicknesses. Multilayer materials can be designed for different food packaging applications and storage conditions, in order to keep the relative humidity of the barrier below recommended 75%, by varying the thickness of the outside versus the inside protective layers and/or varying the water vapour transmission rate of the outside versus the inside layer. The conclusion reached is that to retain the optimal barrier properties and thereby the optimal protection of the food, asymmetric multilayer structures are necessary. Copyright ©2007 John Wiley & Sons, Ltd. [source] Water deprivation tolerance and humidity response in a larval dragonfly: a possible adaptation for survival in drying pondsPHYSIOLOGICAL ENTOMOLOGY, Issue 2 2007MANUELA REBORA Abstract Water deprivation tolerance is investigated in the last larval stadium of Libellula depressa under various conditions of relative humidity (60,100% relative humidity; RH). Most of the larvae maintained at 100% RH emerge and, at lower RH levels show some resistance to dehydration because they die after a mean period ranging from 1.4 days at 60% RH up to 6.7 days at 90% RH. In dual-choice chambers with humidity gradients from 63,74% RH and from 68,84% RH, larvae spend most of the time in the moist side of the chamber. In a Y-tube olfactometer, the larvae reveal a positive hygrotaxis to two airstreams carrying different amounts of water vapour (98% vs. 50%) and spend most of their time in the ,humid' arm. The ecological significance of desiccation tolerance and hygropositive response in the last larval stadium of L. depressa is discussed in relation to the presence of hygroreceptors in dragonfly larvae. [source] Stomatal responses to humidity and temperature in darknessPLANT CELL & ENVIRONMENT, Issue 7 2010KEITH A. MOTT ABSTRACT Stomatal responses to leaf temperature (Tl) and to the mole fractions of water vapour in the ambient air (wa) and the leaf intercellular air spaces (wi) were determined in darkness to remove the potential effects of changes in photosynthesis and intercellular CO2 concentration. Both the steady-state and kinetic responses of stomatal conductance (gs) to wa in darkness were found to be indistinguishable from those in the light. gs showed a steep response to the difference (,w) between wa and wi when wa was varied. The response was much less steep when wi was varied. Although stomatal apertures responded steeply to Tl when ,w was held constant at 17 mmol mol,1, the response was much less steep when ,w was held constant at about zero. Similar results were obtained in the light for ,w = 15 mmol mol,1 and ,w , 0 mmol mol,1. These results are discussed in the context of mechanisms for the stomatal response to humidity. [source] ,18O of water vapour, evapotranspiration and the sites of leaf water evaporation in a soybean canopyPLANT CELL & ENVIRONMENT, Issue 9 2008LISA R. WELP ABSTRACT Stable isotopes in water have the potential to diagnose changes in the earth's hydrological budget in response to climate change and land use change. However, there have been few measurements in the vapour phase. Here, we present high-frequency measurements of oxygen isotopic compositions of water vapour (,v) and evapotranspiration (,ET) above a soybean canopy using the tunable diode laser (TDL) technique for the entire 2006 growing season in Minnesota, USA. We observed a large variability in surface ,v from the daily to the seasonal timescales, largely explained by Rayleigh processes, but also influenced by vertical atmospheric mixing, local evapotranspiration (ET) and dew formation. We used ,ET measurements to calculate the isotopic composition at the sites of evaporative enrichment in leaves (,L,e) and compared that with the commonly used steady-state prediction (,L,s). There was generally a good agreement averaged over the season, but larger differences on individual days. We also found that vertical variability in relative humidity and temperature associated with canopy structure must be addressed in canopy-scale leaf water models. Finally, we explored this data set for direct evidence of the Péclet effect. [source] Evaporative enrichment and time lags between ,18O of leaf water and organic pools in a pine standPLANT CELL & ENVIRONMENT, Issue 5 2007ROMAIN L. BARNARD ABSTRACT Understanding ecosystem water fluxes has gained increasing attention, as climate scenarios predict a drier environment for many parts of the world. Evaporative enrichment of 18O (,18O) of leaf water and subsequent enrichment of plant organic matter can be used to characterize environmental and physiological factors that control evaporation, based on a recently established mechanistic model. In a Pinus sylvestris forest, we measured the dynamics of oxygen isotopic composition (,18O) every 6 h for 4 d in atmospheric water vapour, xylem sap, leaf water and water-soluble organic matter in current (N) and previous year (N-1) needles, phloem sap, together with leaf gas exchange for pooled N and N-1 needles, and relevant micrometeorological variables. Leaf water ,18O showed strong diel periodicity, while ,18O in atmospheric water vapour and in xylem sap showed little variation. The ,18O was consistently lower for N than for N-1 needles, possibly related to phenological stage. Modelled leaf water ,18O showed good agreement with measured values when applying a non-steady state evaporative enrichment model including a Péclet effect. We determined the time lags between ,18O signals from leaf water to water-soluble foliar organic matter and to phloem sap at different locations down the trunk, which clearly demonstrated the relevance of considering these time-lag effects for carbon transport, source-sink and carbon flux partitioning studies. [source] Relationship between plant hydraulic and biochemical properties derived from a steady-state coupled water and carbon transport modelPLANT CELL & ENVIRONMENT, Issue 3 2003G. KATUL ABSTRACT There is growing evidence that plant stomata have evolved physiological controls to satisfy the demand for CO2 by photosynthesis while regulating water losses by leaves in a manner that does not cause cavitation in the soil,root,xylem hydraulic system. Whether the hydraulic and biochemical properties of plants evolve independently or whether they are linked at a time scale relevant to plant stand development remains uncertain. To address this question, a steady-state analytical model was developed in which supply of CO2 via the stomata and biochemical demand for CO2 are constrained by the balance between loss of water vapour from the leaf to the atmosphere and supply of water from the soil to the leaf. The model predicts the intercellular CO2 concentration (Ci) for which the maximum demand for CO2 is in equilibrium with the maximum hydraulically permissible supply of water through the soil,root,xylem system. The model was then tested at two forest stands in which simultaneous hydraulic, ecophysiological, and long-term carbon isotope discrimination measurements were available. The model formulation reproduces analytically recent findings on the sensitivity of bulk stomatal conductance (gs) to vapour pressure deficit (D); namely, gs = gref(1 , m × lnD), where m is a sensitivity parameter and gref is a reference conductance defined at D = 1 kPa. An immediate outcome of the model is an explicit relationship between maximum carboxylation capacity (Vcmax) and soil,plant hydraulic properties. It is shown that this relationship is consistent with measurements reported for conifer and rain forest angiosperm species. The analytical model predicts a decline in Vcmax as the hydraulic capacity of the soil,root,xylem decreases with stand development or age. [source] Atmospheric CO2 concentration does not directly affect leaf respiration in bean or poplarPLANT CELL & ENVIRONMENT, Issue 11 2001S. Jahnke Abstract It is a matter of debate if there is a direct (short-term) effect of elevated atmospheric CO2 concentration (Ca) on plant respiration in the dark. When Ca doubles, some authors found no (or only minor) changes in dark respiration, whereas most studies suggest a respiratory inhibition of 15,20%. The present study shows that the measurement artefacts , particularly leaks between leaf chamber gaskets and leaf surface, CO2 memory and leakage effects of gas exchange systems as well as the water vapour (,water dilution') effect on DCO2 measurement caused by transpiration , may result in larger errors than generally discussed. A gas exchange system that was used in three different ways , as a closed system in which Ca increased continuously from 200 to 4200 mmol (CO2) mol -1 (air) due to respiration of the enclosed leaf; as an intermittently closed system that was repeatedly closed and opened during Ca periods of either 350 or 2000 mmol mol -1, and as an open system in which Ca varied between 350 and 2000 mmol mol -1, is described. In control experiments (with an empty leaf chamber), the respective system characteristics were evaluated carefully. When all relevant system parameters were taken into account, no effects of short-term changes in CO2 on dark CO2 efflux of bean and poplar leaves were found, even when Ca increased to 4200 mmol mol -1. It is concluded that the leaf respiration of bean and poplar is not directly inhibited by elevated atmospheric CO2. [source] Contributions of diffusional limitation, photoinhibition and photorespiration to midday depression of photosynthesis in Arisaema heterophyllum in natural high lightPLANT CELL & ENVIRONMENT, Issue 3 2000Hiroyuki Muraoka ABSTRACT Diurnal changes in photosynthetic gas exchange and chlorophyll fluorescence were measured under full sunlight to reveal diffusional and non-diffusional limitations to diurnal assimilation in leaves of Arisaema heterophyllum Blume plants grown either in a riparian forest understorey (shade leaves) or in an adjacent deforested open site (sun leaves). Midday depressions of assimilation rate (A) and leaf conductance of water vapour were remarkably deeper in shade leaves than in sun leaves. To evaluate the diffusional (i.e. stomatal and leaf internal) limitation to assimilation, we used an index [1,A/A350], in which A350 is A at a chloroplast CO2 concentration of 350 ,mol mol,1. A350 was estimated from the electron transport rate (JT), determined fluorometrically, and the specificity factor of Rubisco (S), determined by gas exchange techniques. In sun leaves under saturating light, the index obtained after the ,peak' of diurnal assimilation was 70% greater than that obtained before the ,peak', but in shade leaves, it was only 20% greater. The photochemical efficiency of photosystem II (,F/Fm,) and thus JT was considerably lower in shade leaves than in sun leaves, especially after the ,peak'. In shade leaves but not in sun leaves, A at a photosynthetically active photon flux density (PPFD) > 500 ,mol m,2 s,1 depended positively on JT throughout the day. Electron flows used by the carboxylation and oxygenation (JO) of RuBP were estimated from A and JT. In sun leaves, the JO/JT ratio was significantly higher after the ,peak', but little difference was found in shade leaves. Photorespiratory CO2 efflux in the absence of atmospheric CO2 was about three times higher in sun leaves than in shade leaves. We attribute the midday depression of assimilation in sun leaves to the increased rate of photorespiration caused by stomatal closure, and that in shade leaves to severe photoinhibition. Thus, for sun leaves, increased capacities for photorespiration and non-photochemical quenching are essential to avoid photoinhibitory damage and to tolerate high leaf temperatures and water stress under excess light. The increased Rubisco content in sun leaves, which has been recognized as raising photosynthetic assimilation capacity, also contributes to increase in the capacity for photorespiration. [source] The quantification of carbon dioxide in humid air and exhaled breath by selected ion flow tube mass spectrometryRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 10 2009David Smith The reactions of carbon dioxide, CO2, with the precursor ions used for selected ion flow tube mass spectrometry, SIFT-MS, analyses, viz. H3O+, NO+ and O, are so slow that the presence of CO2 in exhaled breath has, until recently, not had to be accounted for in SIFT-MS analyses of breath. This has, however, to be accounted for in the analysis of acetaldehyde in breath, because an overlap occurs of the monohydrate of protonated acetaldehyde and the weakly bound adduct ion, H3O+CO2, formed by the slow association reaction of the precursor ion H3O+ with CO2 molecules. The understanding of the kinetics of formation and the loss rates of the relevant ions gained from experimentation using the new generation of more sensitive SIFT-MS instruments now allows accurate quantification of CO2 in breath using the level of the H3O+CO2 adduct ion. However, this is complicated by the rapid reaction of H3O+CO2 with water vapour molecules, H2O, that are in abundance in exhaled breath. Thus, a study has been carried out of the formation of this adduct ion by the slow three-body association reaction of H3O+ with CO2 and its rapid loss in the two-body reaction with H2O molecules. It is seen that the signal level of the H3O+CO2 adduct ion is sensitively dependent on the humidity (H2O concentration) of the sample to be analysed and a functional form of this dependence has been obtained. This has resulted in an appropriate extension of the SIFT-MS software and kinetics library that allows accurate measurement of CO2 levels in air samples, ranging from very low percentage levels (0.03% typical of tropospheric air) to the 6% level that is about the upper limit in exhaled breath. Thus, the level of CO2 can be traced through single time exhalation cycles along with that of water vapour, also close to the 6% level, and of trace gas metabolites that are present at only a few parts-per-billion. This has added a further dimension to the analysis of major and trace compounds in breath using SIFT-MS. Copyright © 2009 John Wiley & Sons, Ltd. [source] Analysis of ketones by selected ion flow tube mass spectrometryRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 23 2003David Smith A selected ion flow tube mass spectrometry (SIFT-MS) study of the reactions of H3O+, NO+ and O2+. ions with the ketones (M) 2-heptanone, 2-octanone, 2-nonanone, 2-undecanone and 2-aminoacetophenone has been conducted in preparation for studies of volatile emissions from bacteria. The H3O+ reactions all proceed rapidly via exothermic proton transfer, producing only MH+ ions that form their monohydrates when water vapour is present in the helium carrier gas. The O2+. reactions proceed rapidly via dissociative charge transfer producing parent cations M+. and some fragment ions. The NO+ reactions form the NO+M adduct ions at rates which are dependent on the pressure of the helium carrier gas. Combining the present NO+ kinetic data with those available from previous SIFT studies, the phenomenon of charge transfer complexing is clearly demonstrated. This results in adduct formation in these NO+/ketone reactions at or near the collisional rate. SIFT-MS spectra are presented to illustrate the simplicity of SIFT-MS analysis of ketones using both H3O+ and NO+ precursor ions. Copyright © 2003 John Wiley & Sons, Ltd. [source] Accuracy and precision of flowing afterglow mass spectrometry for the determination of the deuterium abundance in the headspace of aqueous liquids and exhaled breath waterRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 11 2001Patrik, panel We have assessed the accuracy and precision of our flowing afterglow mass spectrometric method (FA-MS) for absolute measurements of deuterium abundance in water using standardised tap water/D2O mixtures within the D/H range from 155,ppm (local tap water) to 1104,ppm, prepared by the gravimetric method. The results of this study show that a precision and accuracy of 1% can be achieved for the deuterium abundance in water samples. This is quite adequate for the main application, which is the rapid, non-invasive measurement of total body water by deuterium analysis of breath water vapour using the D2O dilution method. Copyright © 2001 John Wiley & Sons, Ltd. [source] Variation in barometric pressure in Melbourne does not significantly affect the BTPS correction factorRESPIROLOGY, Issue 3 2004David P. JOHNS Abstract: The conventional BTPS (body temperature and pressure, saturated with water vapour) correction factor varies with ambient barometric pressure (PB) and many lung function laboratories measure PB daily. The aim was to investigate whether a fixed value for PB could replace daily measurements. PB was measured daily over a 12-month period. The highest and lowest values in Melbourne in the last century were also recorded from data published by the Bureau of Meteorology. Using these PB values, the BTPS factor was determined for a range of spirometer temperatures and compared to the BTPS factors obtained using a fixed ambient pressure of 101.3 kPa. The mean (SD) PB measured over the 12-month period was 102.2 kPa (0.64) with a range of 99.9,103.6 kPa. The level of disagreement between the BTPS factor calculated using a PB of 101.3 kPa instead of the measured value was greater at lower temperatures. Over the extremes of PB during the last century (98.0,104.3 kPa) the use of a standard pressure (101.3 kPa) produced an error in the BTPS factor of ,,0.16%. Daily variations in PB do not significantly affect the magnitude of the conventional BTPS correction factor and a fixed value, such as 101.3 kPa at sea level, can be used with little error. [source] | ||||||||||||||||||||||