Water Vapor Pressure Research Articles

Stomatal conductance reduction tradeoffs in maize leaves: A theoretical study.

As the leading global grain crop, maize significantly impacts agricultural water usage. Presently, photosynthesis ( ) in leaves of modern maize crops is saturated with , implying that reducing stomatal conductance ( ) would not affect but reduce transpiration ( ), thereby increasing water use efficiency (WUE). While reduction benefits upper canopy leaves under optimal conditions, the tradeoffs in low light and nitrogen-deficient leaves under nonoptimal microenvironments remain unexplored. Moreover, reduction increases leaf temperature ( ) and water vapor pressure deficit, partially counteracting transpiratory water savings. Therefore, the overall impact of reduction on water savings remains unclear. Here, we use a process-based leaf model to investigate the benefits of reduced in maize leaves under different microenvironments. Our findings show that increases in due to reduction can diminish WUE gains by up to 20%. However, reduction still results in beneficial WUE tradeoffs, where a 29% decrease in in upper canopy leaves results in a 28% WUE gain without loss in . Lower canopy leaves exhibit superior tradeoffs in reduction with 178% gains in WUE without loss in . Our simulations show that these WUE benefits are resilient to climate change.

Observational relationships between ammonia, carbon dioxide and water vapor under a wide range of meteorological and turbulent conditions: RITA-2021 campaign

Abstract. We present a comprehensive observational approach that aims to establish relationships between the surface–atmosphere exchange of ammonia (NH3) and CO2 uptake and transpiration by vegetation. In doing so, we study relationships useful for the improvement and development of NH3 flux representations in models. The NH3 concentration and flux are measured using a novel open-path miniDOAS (differential optical absorption spectroscopy) measurement setup, taken during the 5-week Ruisdael Land–Atmosphere Interactions Intensive Trace-gas and Aerosol measurement (RITA-2021) campaign (25 August until 12 October 2021) at the Ruisdael Observatory in Cabauw, the Netherlands. After filtering for unobstructed flow, sufficient turbulent mixing and CO2 uptake, we find the diurnal variability in the NH3 flux to be characterized by daytime emissions (0.05 µgm-2s-1 on average) and deposition at sunrise and sunset (−0.05 µgm-2s-1 on average). We first compare the NH3 flux to the observed gross primary production (GPP), representing CO2 uptake, and latent heat flux (LvE), representing net evaporation. Next, we study the observations following the main drivers of the dynamic vegetation response, which are photosynthetically active radiation (PAR), temperature (T) and the water vapor pressure deficit (VPD). Our findings indicate the dominance of the stomatal emission of NH3, with a high correlation between the observed emissions and both LvE (0.70) and PAR (0.72), as well as close similarities in the diurnal variability in the NH3 flux and GPP. However, efforts to establish relationships are hampered by the high diversity in the NH3 sources of the active agricultural region and the low data availability after filtering. Our findings show the need to collocate meteorological, carbon and nitrogen studies to advance our understanding of NH3 surface exchange and its representation.

Patterns in acute aortic dissection and a connection to meteorological conditions in Germany.

Acute type A aortic dissection (ATAAD) is a dramatic emergency exhibiting a mortality of 50% within the first 48 hours if not operated. This study found an absolute value of cosine-like seasonal variation pattern for Germany with significantly fewer ATAAD events (Wilcoxon test) for the warm months of June, July, and August from 2005 to 2015. Many studies suspect a connection between ATAAD events and weather conditions. Using ERA5 reanalysis data and an objective weather type classification in a contingency table approach showed that for Germany, significantly more ATAAD events occurred during lower temperatures (by about 4.8 K), lower water vapor pressure (by about 2.6 hPa), and prevailing wind patterns from the northeast. In addition, we used data from a classification scheme for human-biometeorological weather conditions which was not used before in ATAAD studies. For the German region of Berlin and Brandenburg, for 2006 to 2019, the proportion of days with ATAAD events during weather conditions favoring hypertension (cold air advection, in the center of a cyclone, conditions with cold stress or thermal comfort) was significantly increased by 13% (Chi-squared test for difference of proportions). In contrast, the proportion was decreased by 19% for conditions associated with a higher risk for patients with hypotension and therefore a lower risk for patients with hypertension (warm air advection ahead of warm fronts, conditions with no thermal stress or heat stress, in the center of a cyclone with thermal stress). As many studies have shown that hypertension is a risk factor for ATAAD, our findings support the hypothesized relation between ATAAD and hypertension-favoring weather conditions.

Improving the estimation of atmospheric water vapor pressure using interpretable long short-term memory networks

Atmospheric water vapor pressure is an essential meteorological control on land surface and hydrologic processes. As it is not as frequently observed as other meteorologic conditions, it is often inferred through the August–Roche–Magnus formula by simply assuming dew point and daily minimum temperatures are equivalent or by empirically correlating the two temperatures using an aridity correction. The performance of both methods varies considerably across different regions and during different time periods; obtaining consistently accurate estimates across space and time remains a great challenge. Here, an interpretable Long Short-Term Memory (iLSTM) network conditioned on static, location specific attributes is proposed to estimate the daily vapor pressure. This approach allows for training a single transferable model using ensemble data from multiple sites and exploring the quantitative dependency of vapor pressure prediction on multiple environmental variables and their histories. To evaluate this approach, three iLSTM model configurations were developed, each considering different site attributes as static variables. For each configuration, multiple model realizations were trained using 83 FLUXNET sites in the United States and Canada, where each realization corresponds to different withheld groups of sites used for model evaluation. Results show that the iLSTM networks noticeably improve the estimation accuracy in comparison with the two assumption-based methods for most sites, reducing the failure rate from 32 % to 10.9 % for the best iLSTM model configuration. Additionally, this network provides reasonable insights into both the relative importance of the time-series input variables and their temporal importance. This method is found to be effective for imputing vapor pressure across space and time.

A Hybrid Deep Learning Algorithm for Tropospheric Zenith Wet Delay Modeling with the Spatiotemporal Variation Considered

The tropospheric Zenith Wet Delay (ZWD) is one of the primary sources of error in Global Navigation Satellite Systems (GNSS). Precise ZWD modeling is essential for GNSS positioning and Precipitable Water Vapor (PWV) retrieval. However, the ZWD modeling is challenged due to the high spatiotemporal variability of water vapor, especially in low latitudes and specific climatic regions. Traditional ZWD models make it difficult to accurately fit the nonlinear variations in ZWD in these areas. A hybrid deep learning algorithm is developed for high-precision ZWD modeling, which considers the spatiotemporal characteristics and influencing factors of ZWD. The Convolutional Neural Network (CNN) and Long Short-Term Memory (LSTM) are combined in the proposed algorithm to make a novel architecture, namely, the hybrid CNN-LSTM (CL) algorithm, combining CNN for local spatial feature extracting and LSTM for complex sequence dependency training. Data from 46 radiosonde sites in South America spanning from 2015 to 2021 are used to develop models of ZWD under three strategies, i.e., model CL-A without surface parameters, model CL-B with surface temperature, and model CL-C introducing surface temperature and water vapor pressure. The modeling accuracy of the proposed models is validated using the data from 46 radiosonde sites in 2022. The results indicate that CL-A demonstrates slightly better accuracy compared to the Global Pressure and Temperature 3 (GPT3) model; CL-B shows a precision increase of 14% compared to the Saastamoinen model, and CL-C exhibits accuracy improvements of 30% and 12% compared to the Saastamoinen and Askne and Nordius (AN) model, respectively. Evaluating the models’ generalization capabilities at non-modeled sites in South America, data from six sites in 2022 were used. CL-A shows overall better performance compared to the GPT3 model; CL-B’s accuracy is 19% better than the Saastamoinen model, and CL-C’s accuracy is enhanced by 33% and 10% compared to the Saastamoinen and AN model, respectively. Additionally, the proposed hybrid algorithm demonstrates a certain degree of improvement in both modeling accuracy and generalization accuracy for the South American region compared to individual CNN and LSTM algorithm.

Weakened Increase in Global Near‐Surface Water Vapor Pressure During the Last 20 Years

AbstractIt is well known that global warming increases the atmospheric water vapor content, which results in substantial changes in the hydrological cycle. Using five observational data sets, the results show that an increasing trend of near‐surface water vapor pressure (AVP) over land and ocean was significant from 1975 to 1998, while such an increasing trend in AVP subsequently weakened from 1999 to 2019. This phenomenon is associated with decreased oceanic evaporation and land surface evapotranspiration in response to recent climate variations. One consequence of such a phenomenon is a large increase in near‐surface vapor pressure deficit (VPD), which in turn increases atmospheric demand for water vapor and thus aridity and drought over land. This result emphasizes the importance of water vapor change under global warming.

Controllable van der Waals gaps by water adsorption.

Van der Waals (vdW) gaps with ångström-scale heights can confine molecules or ions to an ultimately small scale, providing an alternative way to tune material properties and explore microscopic phenomena. Modulation of the height of vdW gaps between two-dimensional (2D) materials is challenging due to the vdW interaction. Here we report a general approach to control the vdW gap by preadsorption of water molecules on the material surface. By controlling the saturation vapour pressure of water vapour, we can precisely control the adsorption level of water molecules and vary the height of the vdW gaps of MoS2 homojunctions from 5.5 Å to 53.6 Å. This technique can be further applied to other homo- and heterojunctions, constructing controlled vdW gaps in 2D artificial superlattices and in 2D/3D and 3D/3D heterojunctions. Engineering the vdW gap has great practical potential to modulate the device performance, as evidenced by the vdW-gap-dependent diode characteristics of the MoS2/gap/MoS2 junction. Our work introduces a general strategy of molecular preadsorption that can extend to various precursors, creating more tunability and variability in vdW material systems.

The physico-geometrical reaction pathway and kinetics of multistep thermal dehydration of calcium chloride dihydrate in a dry nitrogen stream.

Several inorganic hydrates exhibit reversible reactions of thermal dehydration and rehydration, which is potentially applicable to thermochemical energy storage. Detailed kinetic information on both forward and reverse reactions is essential for refining energy storage systems. In this study, factors determining the reaction pathway and kinetics of the multistep thermal dehydration of inorganic hydrates to form anhydride via intermediate hydrates were investigated as exemplified by the thermal dehydration of CaCl2·2H2O (CC-DH) in a stream of dry N2. The formation of CaCl2·H2O (CC-MH) as the intermediate hydrate is known during the thermal dehydration of CC-DH to form its anhydride (CC-AH). However, the two-step kinetic modeling based on the chemical reaction pathway considering the formation of the CC-MH intermediate failed in terms of the reaction stoichiometry and kinetic behavior of the component reaction steps. The kinetic modeling was refined by considering the physico-geometrical reaction mechanism and the self-generated reaction conditions to be a three-step reaction. The multistep reaction was explained as comprising the surface reaction of the thermal dehydration of CC-DH to CC-AH and subsequent contracting geometry-type reactions from CC-DH to CC-MH and from CC-MH to CC-AH occurring consecutively in the core of the reacting particles surrounded by the surface product layer of CC-AH. The acceleration of the linear advancement rate of the reaction interface during both contracting geometry-type reactions was revealed through multistep kinetic analysis and was described by a decrease in the water vapor pressure at the reaction interface as the previous reaction step proceeded and terminated.

Nationwide Geospatial Analysis to Identify Variations in Primary Cardiovascular Risk in Ethiopia.

Cardiovascular disease (CVD) varies across regions due to socioeconomic, cultural, lifestyle, healthcare access, and environmental factors. To find geographical variations in 10-year primary CVD risk and assess the impact of contextual factors on CVD risk. Data from 2658 Ethiopians aged 40 to 69 years with no previous CVD who participated in a nationally representative World Health Organization (WHO) STEPS survey in 2015 were included in the analysis. The mean 10-year CVD risk for 450 enumeration areas (EA) was used to identify spatial autocorrelation (using Global Moran's I) and CVD hot spots (using getas-Ord Gi*). Geographically Weighted Regression (GWR) analysis quantified the relationship between mean 10-year CVD risk and climate-related factors across areas. The spatial autocorrelation analysis identified significant spatial variation in the 10-year CVD risk at the EA level, with a global Moran's I value of 0.016. Statistically significant hot spot areas with 10-year CVD risk were identified in Addis Ababa (the capital), Benishangul Gumuz, SNNPR (Southern Nations, Nationalities, and Peoples' Region), Amhara, Afar, Oromia, and Hareri regions. In a multivariable GWR analysis, average water vapor pressure was a statistically significant explanatory variable for the geographical variations in 10-year CVD risk. Hot spot areas for 10-year CVD risk were identified across numerous country regions rather than concentrated in a specific region. Alongside these hot spot areas, regions with a higher annual water vapor pressure (humidity) were identified as geographical targets for CVD prevention.

Establishing a new methodology for determining the water absorbability of cellulose-derived materials via a vapor-monitoring headspace strategy.

In this research, for the first time, we introduce a vapor-monitoring headspace strategy to establish a new methodology for determining the water absorbability of cellulose-derived materials. The method involves detecting the water in the gas phase from various cellulose-derived materials after achieving the equilibrium state. By utilizing the headspace technique to monitor the change in water vapor pressure from bound water to free water, a change point indicating the water absorbability can be identified through fitting procedures. The study showed that the newly-established method possesses high precision (relative standard deviation ≤2.92%) and accuracy (relative differences ≤5.74%) for water absorbability analysis. The present method emerges as a facile and reliable tool for measuring water absorbability, and the introduction of the vapor-monitoring headspace strategy is anticipated to inspire the development of a new type of analytical method.

Short-Term Performance Evaluation of Real-Time Kinematic Global Navigation Satellite System Receivers in Unmanned Aircraft Systems

HighlightsAn evaluation of relative GNSS receiver accuracy was performed using a UAS-based GNSS accuracy testing system.RTK receivers displayed minimal mean error and consistent standard deviations across deployment strategies and error directions.Non-RTK receivers exhibited significantly greater mean error and variability across deployment strategies, particularly in elevation error.UAS deployment strategy did not have a meaningful impact on RTK receiver positioning performance.Abstract. Global navigation satellite system (GNSS) receivers commonly integrated into small unmanned aircraft systems (UAS) generally function in standard or differential fix configurations, providing horizontal and vertical accuracies of approximately ±5 meters and ±15 meters, respectively. The accuracy of GNSS positioning is an important factor with widespread implications, affecting domains such as precision agriculture, meteorology, and photogrammetry. In the context of atmospheric observations, spatial accuracy plays a critical role, particularly in applications related to barometric pressure and precipitable water vapor. Similarly, UAS-based photogrammetry applications rely on high geospatial precision for tasks including topographic mapping and environmental monitoring. As such, this study aimed to improve our understanding of GNSS positioning accuracy in UAS-based observations. The main objectives included (1) deploying a UAS-based GNSS accuracy testing system and (2) evaluating the static and dynamic short-term accuracy of L1 and L1/L2 GNSS receivers in RTK and non-RTK fix modes. Results indicated significant differences across receiver configurations and deployment strategies. RTK receivers displayed minimal mean error and consistent standard deviations, while non-RTK receivers exhibited greater mean error and variability, especially in elevation. Though the study did not conclusively confirm a consistent reduction in accuracy due to UAS deployment, findings suggest that RTK receivers substantially enhance accuracy by reducing position measurement error by two orders of magnitude (1–6 cm for RTK; 50–315 cm for non-RTK), thereby mitigating measurement variability attributable to timing or deployment strategy. In conclusion, this research contributed insights into GNSS accuracy for UAS-based observations and underscored the importance of considering receiver configurations and deployment strategies for position measurement during atmospheric and photogrammetric observations. Keywords: Global navigation satellite systems (GNSS), Meteorology, Photogrammetry, Positioning accuracy, Precision agriculture, Real-time kinematic (RTK), Unmanned aircraft systems (UAS).

Laser-induced fabrication of a supercooled liquid droplet embedded in an ice microcrystal.

Optical heating of an ice microparticle supported on a hydrophobic substrate enabled local melting, yielding a liquid microdroplet. To demonstrate this effect, a liquid droplet entrapped in an ice microcrystal was fabricated by illuminating a focused continuous-wave laser beam in the near-IR at temperatures below -10 °C. Droplets formed in this way are either persistent as a supercooled liquid or short-lived, resulting in recrystallization, depending on the presence of salt additives. Salts were added to reduce the vapor pressure of water because vaporization from ice due to laser heating competed with melting. Without salts, melting occurred only during illumination and there was marked vaporization. In situ Raman micro-spectroscopy assisted by optical microscopy imaging provided clear evidence of liquid water formation at the expense of ice. During illumination, the initial Raman signal of ice was gradually replaced by that of liquid water suggesting that melting proceeded with ice and liquid coexisting. Supercooled droplets embedded in ice microparticles eventually transformed into isolated liquid droplets because the surrounding ice either vaporized or merged into the original droplets. Fundamental features of fabrication based on optical-heating-induced melting were elucidated in the experiments described here.

Water vapor effect on the physico-geometrical reaction pathway and kinetics of the multistep thermal dehydration of calcium chloride dihydrate.

This study investigated how water vapor influences the reaction pathway and kinetics of the multistep thermal dehydration of inorganic hydrates, focusing on CaCl2·2H2O (CC-DH) transforming into its anhydride (CC-AH) via an intermediate of its monohydrate (CC-MH). In the presence of atmospheric water vapor, the thermal dehydration of CC-DH stoichiometrically proceeded through two distinct steps, resulting in the formation of CC-AH via CC-MH under isothermal conditions and linear nonisothermal conditions at a lower heating rate (β). Irrespective of atmospheric water vapor pressure (p(H2O)), these reaction steps were kinetically characterized by a physico-geometrical consecutive process involving the surface reaction and phase boundary-controlled reaction, which was accompanied by three-dimensional shrinkage of the reaction interface. In addition, a significant induction period was observed for the second reaction step, that is, the thermal dehydration of CC-MH intermediate to form CC-AH. With increasing p(H2O), a systematic increase in the apparent Arrhenius parameters was observed for the first reaction step, that is, the thermal dehydration of CC-DH to form CC-MH, whereas the second reaction step exhibited unsystematic variations of the Arrhenius parameters. At a larger β in the presence of atmospheric water vapor, the first and second reaction steps partially overlapped; moreover, an alternative reaction step of the thermal dehydration of CC-MH to form CaCl2·0.3H2O was observed between these reaction steps. The physico-geometrical phenomena influencing the reaction pathway and kinetics of the multistep thermal dehydration were elucidated by considering the effects of atmospheric and self-generated water vapor in a geometrically constrained reaction scheme.

Global zenith wet delay modeling with surface meteorological data and machine learning

The tropospheric delay is a major error source for space geodetic techniques, and the performance of its modeling is significantly limited due to the high spatiotemporal variability of the moisture in the lower atmosphere. In this study, global modeling of the tropospheric zenith wet delay (ZWD) was realized based on surface meteorological data obtained from radiosondes and Global Positioning System (GPS) radio occultation (RO) measurements through the random forest (RF) and backpropagation neural network (BPNN) regression analysis. The modeling performance was further validated based on two kinds of global atmospheric profiles for the year 2020. Our results show that the ZWD modeling accuracy gained by two machine learning regression approaches is significantly improved by taking into account surface meteorological parameters, especially the surface water vapor pressure when compared to the Global Pressure and Temperature 3 (GPT3) model. When surface meteorological data are available, the RF-B model yields ZWD estimations with an overall agreement of 3.1 cm in comparison with the sounding profiles and 2.4 cm in contrast to the GPS RO atmospheric profiles. The RF-B is superior to other models based on surface meteorological parameters for ZWD calculation, e.g., the accuracy improves by 21.8–23.8% against the approach by Saastamoinen and 7–12.2% against the formula by Askne and Nordius.

Solar light driven atomic and electronic transformations in a plasmonic Ni@NiO/NiCO3 photocatalyst revealed by ambient pressure X-ray photoelectron spectroscopy.

This work employs ambient pressure X-ray photoelectron spectroscopy (APXPS) to delve into the atomic and electronic transformations of a core-shell Ni@NiO/NiCO3 photocatalyst - a model system for visible light active plasmonic photocatalysts used in water splitting for hydrogen production. This catalyst exhibits reversible structural and electronic changes in response to water vapor and solar simulator light. In this study, APXPS spectra were obtained under a 1 millibar water vapor pressure, employing a solar simulator with an AM 1.5 filter to measure spectral data under visible light illumination. The in situ APXPS spectra indicate that the metallic Ni core absorbs the light, exciting plasmons, and creates hot electrons that are subsequently utilized through hot electron injection in the hydrogen evolution reaction (HER) by NiCO3. Additionally, the data show that NiO undergoes reversible oxidation to NiOOH in the presence of water vapor and light. The present work also investigates the contribution of carbonate and its involvement in the photocatalytic reaction mechanism, shedding light on this seldom-explored aspect of photocatalysis. The APXPS results highlight the photochemical reduction of carbonates into -COOH, contributing to the deactivation of the photocatalyst. This work demonstrates the APXPS efficacy in examining photochemical reactions, charge transfer dynamics and intermediates in potential photocatalysts under near realistic conditions.

2012–2016年三江源垂穗披碱草人工草地碳水热通量观测数据集

In the Sanjiangyuan Area known as the “Chinese Water Tower”, planting perennial artificial grassland has become an important measure for the restoration of degraded grassland in this area. The spatial-temporal pattern of the carbon, water, and heat fluxes of Elymus nutans artificial grasslands are crucial for comprehending the ecological service functions of the Elymus nutans artificial grasslands in the Sanjiangyuan Area. Sanjiangyuan Grassland Ecosystem National Observation and Research Station (referred to as Sanjiangyuan Sation) has used the eddy covariance technique to monitor the carbon, water, and heat fluxes over an Elymus nutans artificial grassland for 5 years since 2009. In order to advance the research on carbon, water, and heat fluxes and other related researches in the Sanjiangyuan Area and the broader Qinghai-Tibetan Plateau alpine ecosystems, we plan to publish the routine meteorological data of carbon, water and heat fluxes over an Elymus nutans artificial grassland observed from 2012 to 2016. This dataset includes routine meteorological data (i.e. air temperature, air relative humidity, water vapor pressure, soil temperature, soil moisture, photosynthetically active radiation, and precipitation) and carbon, water, and heat fluxes data (net ecosystem CO2 exchange, ecosystem CO2 respiration, gross ecosystem CO2 exchange, latent heat flux, and sensible heat flux) on half-hourly, daily, monthly, and yearly scales. The dataset used the flux data processing method recommended by ChinaFLUX. It is expected to provide field observational data support for scientific understanding, remote sensing retrieval processes, and model validation efforts in exploring the spatiotemporal patterns of carbon, water, and heat exchanges in artificial Elymus nutans grasslands.

Characterization of Water Vapor Sorption Performance and Heat Storage of MIL-101 (Cr) Complex MgCl2, LiCl/LaCl3 System for Adsorptive Thermal Conversion.

Adsorption heat conversion systems can provide heating and cooling across time and space in a more environmentally friendly way. Porous materials are potential candidates for water-based adsorption thermal conversion, in which a metal-organic framework (MOF) has a larger specific surface area and porosity than other porous matrices. However, many MOFs with high saturated adsorption capacity have great deficiencies in performance at low water vapor partial pressure, which hinder their application in adsorption thermal conversion. To improve the water vapor adsorption performance of MIL-101 (Cr), different contents of magnesium chloride, lithium chloride, and lanthanum chloride are mixed into MIL-101 (Cr) by an impregnation method. The properties and structures of the materials are characterized by XRD, SEM, nitrogen adsorption tests, water vapor adsorption tests, TG, FTIR, and so on. The results show that the saturated water vapor adsorption capacity of the sample impregnated with salt increases by 1.5-2.3 times, up to 2.24 g/g, compared with that of the unimpregnated sample. When the partial pressure of water vapor is 0.3, the adsorption capacity increases by 5.3-7.5 times and reaches 0.68 g/g at most. The maximum heat storage density of impregnated samples can be increased by 866 J/g. Impregnated MgCl2 can greatly improve the adsorption and thermal conversion performance of MOF, and impregnated MgCl2 and the proper amount of LiCl can further improve the performance of the material system. Our experiments show that the composite impregnation of magnesium chloride and the proper amount of lithium chloride can improve the application performance of the MOF materials in the adsorption thermal conversion process.

Operando 3D-Monitoring of the Oxygen Partial Pressure (p(O2)) within a Polymer Electrolyte Membrane Fuel Cell (PEMFC) during Cell Operations at Higher Temperatures

Introduction:Hydrogen technologies, especially the Proton Exchange Membrane Fuel Cell (PEMFC), are promising alternative power sources, due to their low to non-carbon emission, high power density, high efficiency, and fast start-up. Despite their high potential and expected major impact on the economy of the future, there are still challenges to overcome, before PEMFCs can be globally commercialized. Soon, PEMFCs operated above 100°C are expected to be used for automobiles, due to their use of smaller and lighter radiators, higher reaction rates and lower susceptibility to catalyst poisoning. To achieve this goal however, high-temperature PEMFCs need a higher performance, stability, and durability, while reducing the cost at the same time. The performance, durability and stability of a fuel cell are related to the distribution of physical and chemical parameters, like e.g., oxygen partial pressure (p(O2)). During the operation of the fuel cell, the distribution of those parameters is inhomogeneous.[1] Therefore, we used an in-house developed 3-dimensional non-destructive real-time/space visualization system to achieve an understanding of the p(O2) inside the fuel cell during operation at higher temperatures.Experimental:The PEMFC used for this experiment has an active area of 4 cm2 and uses 10 straight gas flow channels. Prior to the assembling, 5 pinholes with a diameter of 90 µm were manufactured into the GDL on the cathode side both underneath the rib and the gas flow channel (Fig. 1). Those pinholes are also manufactured into the current collector and insulator of the PEMFC on cathode side. The holes are used to insert optical fibers from outside the cell to approximately 20 µm (adjustable with an accuracy of 1 µm) above the catalyst layer of the CCM. Prior to the use, the fibers with a core diameter of 10 µm are etched in HF solution to reduce their clad diameter from 125 to 50 µm. Furthermore, the apex of the fiber is cleaved perpendicular to the axis of the fiber. Before insertion an oxygen sensitive dye (PtTFPP, (Fig. 2)) is applied to the apex of the fibers. PtTFPP has absorption peaks at 407, 530 and 540 nm and an emission peak at 650 nm. The emission peak is quenched by oxygen partial pressure, and the emission intensity decreases monotonically with increasing oxygen partial pressure. For the excitation, a laser with a wavelength of 532 nm is used and the emitted light is captured by a CCD camera.[2] Visualizations were carried out at 80, 90, 100, 110 and 120 oC at a constant water vapor pressure of 37.97 kPa, which equals 80, 53.6, 36.8, 25,9 and 18.5% RH respectively, at increasing current densities. Prior to the visualization, calibrations, and performance tests in form of IV and CV were carried out for each temperature. The gas flow rate during the experiments was set to 100 mL/min Air/H2 (parallel flow) at cathode and anode respectively. Results and Discussion:The IV performance tests showed decreasing cell performance with increasing temperatures, which was expected because of the increasing resistance due to drying out of the membrane. Furthermore, a decrease of the ECSA was observed with increasing temperatures, which could also be due to the drying out of the membrane as well as the binding material around the catalyst nanoparticles which reduces gas diffusion and the effective catalyst surface area. In this first try, the monitoring was done with 3 fibers under one rib located near the inlet, the middle of the cell and near the outlet of the cell. With increasing current density, the oxygen partial pressure was decreasing at every temperature. Interestingly, the oxygen partial pressure distribution changed with increasing temperature. The reason for the changing oxygen partial pressure distribution could be due to accumulation of heat (Fig. 3) and increasing water vapor pressure at higher temperatures. Further experiments with 5 fibers including measurements in the gas flow channel as well as measurements with back pressure to increase the cell performance will be done shortly to confirm this finding.[1] Y. Kakizawa, C. L. Schreiber, S. Takamuku, M. Uchida, A. Iiyama, J. Inukai, Visualization of the oxygen partial pressure in a proton exchange membrane fuel cell during cell operation with low oxygen concentrations, J. Power Sources, 483, 229193 (2021).[2] Y. Kakizawa, T. Kobayashi, M. Uchida, T. Ohno, T. Suga, M. Teranishi, M. Yoneda, T. Saiki, H. Nishide, M. Watanabe, A. Iiyama, J. Inukai, Oscillation mechanism in polymer electrolyte membrane fuel cell studied by operando monitoring of oxygen partial pressure using optical probes, J. Surf. Finish. Soc. Jpn, 72, 230 (2021). Figure 1

Sunscreen does not alter sweating responses or critical environmental limits in young adults (PSU HEAT project).

Outdoor athletes often eschew using sunscreen due to perceived performance impairments, which many attribute in part to the potential for reduced thermoregulatory heat loss. Past studies examining the impact of sunscreen on thermoregulation are equivocal. The purpose of this study was to determine the effects of mineral and chemical-based sunscreens on sweating responses and critical environmental limits in hot-dry (HD) and warm-humid (WH) environments. Nine subjects (3 M/6 F; 25 ± 2 yr) were tested with 1) no sunscreen (control), 2) chemical-, and 3) mineral-based sunscreen. Subjects were exposed to progressive heat stress with either 1) constant dry-bulb temperature (Tdb) at 34°C and increasing water vapor pressure (Pa) (WH trials) or 2) constant Pa at 12 mmHg and increasing Tdb (HD trials). Subjects walked at 4.9 ± 0.5 metabolic equivalents (METs) until an upward inflection in gastrointestinal temperature was observed (i.e., the critical environmental limit). Compared with control (39.9 ± 3.0°C), critical Tdb was not different in mineral (39.2 ± 3.5°C, P = 0.39) or chemical (39.7 ± 3.0°C, P = 0.98) sunscreen trials in HD environments. Compared with control (18.8 ± 4.0 mmHg), critical Pa was not different in mineral (18.9 ± 4.8 mmHg, P = 0.81) or chemical (19.5 ± 4.6 mmHg, P = 0.81) sunscreen trials in WH environments. Sweating rates, evaporative heat loss, skin wettedness, and sweating efficiency were not different among the three trials in the WH (all P ≥ 0.48) or HD (all P ≥ 0.87) environments. Critical environmental limits are unaffected by sunscreen application, suggesting sunscreen does not alter integrative thermoregulatory responses during exercise in the heat.NEW & NOTEWORTHY Our findings demonstrate that neither sweating nor critical environmental limits were affected by mineral-based and chemical-based sunscreen applications. The rates of change in core temperature during compensable and uncompensable heat stress were not changed by wearing sunscreen. Evaporative heat loss, efficiency of sweat evaporation, skin wettedness, and sweating rates were unaffected by sunscreen. Sunscreen did not alter integrative thermoregulatory responses during exercise in the heat.

Transpiration rates from mature Eucalyptus grandis × E. nitens clonal hybrid and Pinus elliottii plantations near the Two Streams Research Catchment, South Africa

Abstract. Pine plantations are the dominant species currently planted within the South African commercial forestry industry. Improvements in bio-economy markets for dissolving wood pulp products have seen an expansion in fast-growing Eucalyptus plantations due to their higher productivity rates and better pulping properties than pine. This has raised concerns regarding the expansion of Eucalyptus plantations and how they will affect water resources as they have been reported to have higher water use (quantified using transpiration rates) than pine. We measured transpiration rates (mm yr−1), diameter at breast height (quantified as quadratic mean diameter, Dq, m) and leaf area index of an 8-year-old Eucalyptus grandis × Eucalyptus nitens clonal hybrid (GN) and a 20-year-old Pinus elliottii. Transpiration rates were measured for two consecutive hydrological years (2019/20 and 2020/21) using a heat ratio sap-flow method, calibrated against a lysimeter. In the 2019/20 year, annual transpiration for P. elliottii exceeded GN by 28 %, while for the 2020/21 hydrological year, there was no significant difference between the transpiration of the two species, despite a 17 % and 21 % greater leaf area index for P. elliottii than GN in 2019/20 and 2020/21 measurement years respectively. Quadratic mean diameter increments were statistically similar (p > 0.05) in 2019/20, whereas the 2020/21 year produced significant differences (p<0.05). Tree transpiration is known to be influenced by climatic variables; therefore, a random forest regression model was used to test the level of influence between tree transpiration and climatic parameters. The soil water content, solar radiation and vapour pressure deficit were found to highly influence transpiration, suggesting these variables can be used in future water-use modelling studies. The profile water content recharge was influenced by rainfall events. After rainfall and soil profile water recharge, there was a rapid depletion of soil water by the GN trees, while the soil profile was depleted more gradually at the P. elliottii site. As a result, trees at the GN site appeared to be water stressed (reduced stem diameters and transpiration), suggesting that there was limited access to alternative water source (such as groundwater). The study concluded that previous long-term paired catchment studies indicate that eucalypts use more water than pine; however, periods of soil water stress and reduced transpiration observed in this study must be accommodated in hydrological models. Long-term total soil water balance studies are recommended in the same region to understand the long-term impact of commercial plantations on water resources.