Atmospheric Vapor Research Articles

Low temperature thermally reduced graphene oxide directly on Ni-Foam using atmospheric pressure-chemical vapour deposition for high performance supercapacitor application

A binder free approach was use to prepare thermally reduced graphene oxide (TRGO) at 200 °C directly on Ni-Foam (NF) (current collector) via atmospheric pressure-chemical vapour deposition (AP-CVD) and used as a positive electrode for supercapacitor application. The TRGO/NF electrode preparation method is simpler, quicker, cheaper and more effective compared to other method. The half-cell electrochemical performances in 6 M KOH showed a maximum specific capacity of 52.64 mA h g−1 at 0.5 A g−1. The device: TRGO/NF//PAC showed a specific energy and power of 18.72 Wh kg−1 and 547.52 W kg−1 respectively at 1 A g−1; and 14.10 Wh kg−1 and 2.5 kW kg−1 respectively at 5 A g−1. The high coulombic efficiency (99.9%) and capacitance retention (70%) indicate outstanding stability. These results represent a significant progress in the fabrication of binder and conductive enhancement free positive electrode for electrochemical energy storage devices.

Temporal variation in stomatal sensitivity to vapour pressure deficit in western riparian forests

Abstract Increasing atmospheric vapour pressure deficit (D) can influence plant water and carbon uptake. However, growing season variation in stomatal responses to D among tree taxa has not been thoroughly quantified and therefore has not been well‐characterized in stomatal regulation models. Using sap flux data from nine riparian species spanning a 600‐m elevation gradient in semi‐arid northern Utah, USA, we fit a time‐varying empirical model of stomatal conductance to D in a hierarchical Bayesian framework. The reference conductance (Gref, conductance at D = 1 kPa) term was modelled as a function of cumulative growing season D, which varied with site elevation. Seven species exhibited Gref that varied significantly with cumulative growing season D, but the direction was not consistent among species. Two low‐elevation ring‐porous species, the invasive Tamarix ramosissima and Elaeagnus angustifolia, exhibited significantly positive correlation between Gref and cumulative D, such that standardized stomatal sensitivity (S) decreased during the season. Despite lower D at the mid‐ and high‐elevation sites, five diffuse‐porous native species exhibited progressively increasing sensitivity to D during the growing season. Stomatal strategies exhibit seasonal trends that vary by environmental conditions (D) and functional traits (wood anatomy), which complicates the prediction of plant hydraulic function under increasing atmospheric drought. In the increasingly arid western United States, the progressively less sensitive stomatal behaviour of invasive taxa may hasten their dominance in riparian forests. Read the free Plain Language Summary for this article on the Journal blog.

Experimental Analysis of Atmospheric Ducts and Navigation Radar Over-the-Horizon Detection

Since the height of sea detection radar antenna and ship targets is relatively low, it is generally believed that its over-the-horizon detection is mainly caused by the evaporation duct at sea. To fully understand the influence of atmospheric ducts on radar over-the-horizon detection, a shore-based navigation radar was used to carry out over-the-horizon detection experiments; radiosondes were used to measure the atmospheric profile and evaporation duct monitoring equipment was used to measure the evaporation duct. Based on experimental data and model simulation, a comparative analysis of a navigation radar’s over-the-horizon detection, the evaporation duct, and the lower atmospheric duct is presented in this study. The results show that the atmospheric duct can affect the signal propagation of the navigation radar, thus resulting in over-the-horizon detection. The long-range over-the-horizon detection of the navigation radar is caused by the strong lower atmospheric duct, while the evaporation duct can generally only form weak over-the-horizon detection, which is different from the general cognition.

Effect of Water Vapor on the Microstructure of Al2O3 on the Free-Standing MCrAlY Alloy at 1100 °C

The oxidation resistance of the MCrAlY binding coat is due to the formation of protective Al2O3 oxide scale at high temperature. The oxidation behavior of NiCrAlYHf alloy in 1100 °C air and air-water vapor atmosphere was studied. The effect of water vapor on the microstructure and distribution of reactive elements was discussed. The results showed that the oxide scale in air has a double layer structure composed of columnar and equiaxed crystals, while the oxide scale in water vapor contains fine alumina grains, which provides more channels for the diffusion of reactive elements. In addition, The Cr element in the oxide scale is mainly concentrated in the outer equiaxed crystal zone, and the Hf oxide is mainly concentrated in the columnar crystal boundary. In air-water vapor atmosphere, the Cr element is uniformly distributed in the oxide scale.

Tropical tree mortality has increased with rising atmospheric water stress.

Evidence exists that tree mortality is accelerating in some regions of the tropics1,2, with profound consequences for the future of the tropical carbon sink and the global anthropogenic carbon budget left to limit peak global warming below 2 °C. However, the mechanisms that may be driving such mortality changes and whether particular species are especially vulnerable remain unclear3-8. Here we analyse a 49-year record of tree dynamics from 24 old-growth forest plots encompassing a broad climatic gradient across the Australian moist tropics and find that annual tree mortality risk has, on average, doubled across all plots and species over the last 35years, indicating a potential halving in life expectancy and carbon residence time. Associated losses in biomass were not offset by gains from growth and recruitment. Plots in less moist local climates presented higher average mortality risk, but local mean climate did not predict the pace of temporal increase in mortality risk. Species varied in the trajectories of their mortality risk, with the highest average risk found nearer to the upper end of the atmospheric vapour pressure deficit niches of species. A long-term increase in vapour pressure deficit was evident across the region, suggesting that thresholds involving atmospheric water stress, driven by global warming, may be a primary cause of increasing tree mortality in moist tropical forests.

Controllable growth of large-area 1T′, 2H ultrathin MoTe2 films, and 1T′–2H in-plane homojunction

Atomically thin molybdenum ditelluride (MoTe2) has been intensively studied as an emerging material for electronics and optoelectronics due to its unique properties. While the small free energy difference between the 2H and 1T′ phases of MoTe2 always results in mixed-phase growth, precisely controlled phase transition of MoTe2 nanostructures is still a considerable challenge. Here, the centimeter-scale 1T′, 2H ultrathin MoTe2 films, and in-plane 1T′–2H homojunction have been synthesized by ambient pressure chemical vapor deposition based on the precursor design and space-confined strategies. The controllable growth of pure 1T′, 2H MoTe2, and 1T′–2H mixed-phase MoTe2 with phase separation and homogeneous mixture, respectively, has been achieved by adjusting growth temperature and growth time. The thickness of synthesized 1T′ and 2H ultrathin MoTe2 films can be effectively controlled by tuning the space-confined height. The corresponding growth mechanism was further illuminated based on systematically experimental characterizations and computational fluid dynamics simulations. The electrical transport properties of 1T′ and 2H MoTe2 films were investigated by conductive atomic force microscope and MoTe2-based thin-film field-effect transistors. Our experimental results provide a new route to realize the phase transition of two-dimensional materials, which makes these materials easily accessible as functional building blocks for next-generation electronic and optoelectronic devices.

Modification of the vacuum-steam thawing method of meat by using the initial stage of sublimation dehydration

Vacuum-steam thawing is one of the methods used for defrosting food, realized in the atmosphere of water vapour under the conditions of reduced pressure. The water vapour formed in vacuum with the temperature of 20 °C fills the defrosting chamber and condenses on the surface of the defrosted product. The condensated steam has the role of thermal energy carried enabling product thawing. The study presents a modification of this method, introducing an additional stage of sublimation-dehydration vacuum steam thawing (SRVST). The study was carried out for different variants of initial sublimation degree (in the range from 0 to 15%) of a slice of pork loin (m. longissimus lumborum) assessing the final effect of the process of vacuum-steam thawing. Thawing kinetics was determined with the SRVST method, degree of sample defrosting and level of their rehydration. Based on the results it was demonstrated that the use of 12% sublimation dehydration of a meat sample enables its complete defrosting (reaching the temperature not exceeding the cryoscopic temperature).

Towards a Generalized ORR Mechanism in M2+‐Containing DMSO: Oxygen Reduction and Evolution in Ca2+‐Containing DMSO on Atomically Smooth and Rough Pt

AbstractThe oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in Ca2+ containing dimethyl sulfoxide (DMSO) on atomically smooth Pt(111) and Pt(100) and rough Pt surfaces is reported. As demonstrated by cyclic voltammetry and XPS, the bromine adlayer used to protect Pt single crystals against ambient air and solvent vapor is desorbed in DMSO and does not affect the following measurements. Cyclic voltammetry, differential electrochemical mass spectrometry (DEMS), and rotating ring disk electrode (RRDE) investigations with variation of the electrode surface roughness and atomically surface structure show, that on Pt electrodes the CaO2 adsorbate layer formation determines the ORR product distribution. On Pt electrodes, calcium peroxide is formed on the clean electrode, whereas calcium superoxide is formed at the adsorbate covered electrode. We furthermore identified four key parameters, which strongly affect the ORR product distribution: 1) The electrode oxide interaction: A strong interaction increases superoxide contribution; 2) The alkaline earth metal oxide interaction: A strong interaction increases peroxide contribution; 3) The electrode surface area: A large electrode surface area increases peroxide contribution; 4) Electrode surface defects: Defects increase superoxide contribution. Finally, reviewing earlier results of our group, we provide a more general mechanism for the oxygen reduction alkaline earth metal cation containing DMSO, for a variety of electrode materials.

Reversible and Stepwise Single-Crystal-to-Single-Crystal Transformation of a Platinum(II) Complex with Vapochromic Luminescence.

The vapochromic single-crystal-to-single-crystal (SCSC) transformation of a highly luminescent PtII complex bearing an N-heterocyclic carbene [Pt(CN)2 (tBu-impy)] (tBu-impyH+ =1-tert-butyl-3-(2-pyridyl)-1H-imidazolium) is reported. The trihydrate form of the complex, which exhibits blue 3 MMLCT emission owing to weak Pt⋅⋅⋅Pt interactions, changed its luminescence color from blue to yellowish-green upon the desorption of water molecules while keeping the high emission quantum yield of more than 0.45. Variable-temperature and continuous in-situ tracking of single-crystal X-ray diffraction measurements revealed that the SCSC transformation proceeds reversibly by the release and reabsorption of water molecules, thereby changing the stacked structure slightly. As a result, the dynamics of vapor-induced SCSC transformation were elucidated: that the anhydrous form returned to the original trihydrate form in a two-step process under a water vapor atmosphere. In addition, the PtII complex exhibited a similar SCSC response accompanied by a luminescence color change in the presence of methanol vapor, while being inactive toward ethanol vapor.

Diurnal Variations of Water Ice in the Martian Atmosphere Observed by Mars Climate Sounder

Simulation studies have proposed a significant thermal effect of water ice clouds on the Martian atmosphere and climate. However, previous studies focused more on seasonal variations but less on short-term changes. In this work, we used the MCS multi-local time data to investigate the water ice diurnal variations on Mars. We quantified its diurnal variations with amplitude and phase by applying the tidal fitting method to the water ice abundance. In addition, we found a close correlation (antiphase relation) between the thermal tide and water ice diurnal variations during the aphelion seasons that was not sensitive to both the background water ice and dust opacity but increased with the tidal amplitude. In the perihelion seasons, the antiphase relation was sensitive to the water ice and dust opacity, both affected by the dust storm activity. Finally, the statistic results suggested an unexpected low threshold of diurnal tide amplitude (2 to 3 K) for generating a relevant water ice diurnal variation, accounting for the ubiquitous water ice diurnal variations in the Martian atmosphere. These new observational results can help further understand the phase transition process between ice and vapor in the Martian atmosphere and better constrain the Martian global climate model in the future.

Energy and evapotranspiration partitioning over a humid region orchard: Field measurements and partitioning model comparisons

Understanding energy and water flux cycling and quantifying their components are essential steps to elucidate the hydrological process and sustainable water resources management in agricultural ecosystems. The challenge of partitioning energy and evapotranspiration (ET) components (canopy transpiration Tc and surface evaporation Es) was addressed by the combination of eddy covariance (EC) technique, micro-lysimeters, and sap flow methods in a humid region kiwifruit orchard of Southwest China. The variations of energy and water flux and their controls were assessed, then the measured ET and its component were compared with the simulated values by Priestley-Taylor Jet Propulsion Laboratory model (PT-JPL), Shuttleworth-Wallace (S-W), and FAO-56 dual crop coefficient models (Dual-FAO). The results showed that latent heat flux (LE) dominated the consumption of net radiation energy (Rn), with the averaged ratio (EF = LE/Rn) above 0.70 during the growing seasons. More radiation energy is released in the form of LE with increased surface moisture and vegetation cover (total leaf area index, LAIt). Tc accounted for 41%–46% ET. The increase of canopy leaf area index (LAIc) strongly affected ET partitioning through the early growing seasons, while atmospheric evaporation demand dominated the Tc/ET and even caused the energy to be redistributed since high atmospheric evaporation demand caused a decrease of Tc while an increase of Es during the active growing seasons (LAIc > 2.5 m2 m−2). All the ET models performed well in estimating ET (R2 = 0.84–0.92) and its components (Tc, R2 = 0.70–0.74; Es, R2 = 0.63–0.69), allowing individual estimation of water interception by the canopy is one of the merits of the PT-JPL model for ET simulation in this humid site, with R2 of 0.92, RMSE of 0.55 mm d−1, while the S-W model performed slightly better in ET component simulations (Tc, R2 = 0.74, RMSE = 0.35 mm d−1; Es, R2 = 0.69, RMSE = 0.38 mm d−1). The results of our study may have much referential significance for eco-hydrological process analysis and water flux estimation in regions with similar environmental conditions.

Critical Environmental Limit Protocol: Validity and Reliability (PSU HEAT)

With increasing average global temperatures and greater frequency, duration, and severity of heat waves, there is an urgent need to better understand the specific environmental temperatures that place humans at greater risk of heat‐related morbidity and mortality. An incremental heat stress protocol can be used to establish critical environmental limits for human heat exchange, i.e., those combinations of ambient temperature and humidity above which heat stress becomes uncompensable and, therefore, unsafe. However, no studies have rigorously investigated the reliability and validity of this experimental paradigm.PURPOSEHere, we assessed the (1) between‐visit repeatability and (2) validity of an experimental paradigm that either holds ambient vapor pressure (Pa) constant and incrementally increases dry‐bulb temperature (Tdb) or vice versa.METHODSTwelve subjects (5M/7W; 25±4 yr) completed a progressive heat stress protocol during which they walked on a treadmill (2.2 mph, 3% gradient) in a controllable environmental chamber while gastrointestinal temperature (Tgi) was continuously monitored. After an equilibration period, the progressive heat stress protocol involved increasing Tdb every 5 min while Pa was held constant (Tcritexperiments), or increasing Pa every 5 min while Tdb was held constant (Pcritexperiments), until an upward inflection and continuous rise in Tgi was observed. The Tcrit or Pcrit was identified as the average Tdb or Pa, respectively, across the 2 min preceding the Tgi inflection point. For repeatability experiments, 11 subjects returned to the lab to repeat the same protocol as their first visit. For validity experiments, 10 subjects returned to the lab for a progressive heat stress trial in which Tdb or Pa was held constant at the Tcrit or Pcrit value from their first visit.RESULTSThe between‐visit repeatability for critical environmental limits was excellent (ICC = 0.98). Similarly, there was excellent agreement between original and validity trials for Tdb (ICC = 0.95) and Pa (ICC = 0.96) at the Tgi inflection point. Furthermore, the wet‐bulb temperature at the Tgiinflection point was not different during reliability (p = 0.78) or validity (p = 0.32) trials compared to original trials.CONCLUSIONTogether, these data provide strong evidence that this experimental paradigm is rigorous, reliable, and valid, supporting its use to investigate critical environmental limits to the maintenance of heat balance.

Exoplanet X-ray irradiation and evaporation rates with eROSITA

High-energy irradiation is a driver for atmospheric evaporation and mass loss in exoplanets. This work is based on data from eROSITA, the soft X-ray instrument on board the Spectrum Roentgen Gamma mission, as well as on archival data from other missions. We aim to characterise the high-energy environment of known exoplanets and estimate their mass-loss rates. We use X-ray source catalogues from eROSITA, XMM-Newton, Chandra, and ROSAT to derive X-ray luminosities of exoplanet host stars in the 0.2–2 keV energy band with an underlying coronal, that is, optically thin thermal spectrum. We present a catalogue of stellar X-ray and EUV luminosities, exoplanetary X-ray and EUV irradiation fluxes, and estimated mass-loss rates for a total of 287 exoplanets, 96 of which are characterised for the first time based on new eROSITA detections. We identify 14 first-time X-ray detections of transiting exoplanets that are subject to irradiation levels known to cause observable evaporation signatures in other exoplanets. This makes them suitable targets for follow-up observations.

Preparation of Hierarchically Porous Metal-Organic Frameworks via Slow Chemical Vapor Etching for CO2 Cycloaddition.

Hierarchically porous metal-organic frameworks (HP-MOFs) are a class of promising functional material with micropores, mesopores, and/or macropores, which can address the issue of slow mass transfer and less exposed active sites for primitive microporous MOFs. Despite many attempts that have been achieved through a variety of techniques to date, there is still a myriad of spaces that urgently need to be exploited. In this work, we report the novel synthesis of HP-MOFs via slow chemical steam etching. The preparation process can be subtly achieved using water vapor as an etchant; meanwhile, the addition of ethanol into the vapor atmosphere is carried out because it can stabilize the MOF framework well with its hydrophobic alkane tails, thereby slowing the etching rate toward MOFs, successfully realizing the controllable etching manner of MOF components. Furthermore, the joint influence of the water content and etching temperature on the MOF backbone structure etched has thus been investigated in detail. Impressively, we can harvest desired HP-MOFs with the retained crystalline structure at a water content of 50% and an etching temperature of 120 °C. The resulting HK-120/50 product etched exhibits excellent catalytic activity and stability in [2 + 3] cycloaddition of CO2 than pristine MOF, which can be attributed to the more exposure of active sites and the acceleration of mass transportation across the entire MOF skeleton. Noteworthy, the strategy proposed in this study may be extended to other HP-MOF construction systems due to the lability of most MOFs toward the chemical water vapor.

Mesoscale Simulations on the Ultrahigh Heat Flux Evaporation of R143a within Ultrathin Nanoporous Membrane Using a Modified Dimensionless Lattice Boltzmann Method

A modified dimensionless pseudo-potential lattice Boltzmann method capable of restoring all related thermophysical properties of any working fluid and spatial/temporal scales of the computational domain is developed in this work. Direct numerical investigations of ultrathin liquid film evaporation of R143a within nanoporous membranes to its ambient pure vapor are carried out. The characteristics of evaporation-driven replenishing flow and the self-regulation of liquid-vapor interface profile under different heat fluxes are captured. In the case of intensive ultrathin liquid film evaporation within nanopore, the apparent contact angle could not reach as small as Young's contact angle θ0 for isothermal conditions due to the self-regulation of liquid-vapor interface. As a result, the maximum capability of nanoporous membranes to replenish the liquid is limited. Under the ambient temperature T0 = 318.19 K, before the three-phase contact line (TCL) recedes into the nanoporous membrane, a heat flux as high as qin,max = 1.52 kW/cm2 can be sustained with a superheat about Ts = 7.79 K for a membrane with pore radius rp = 38.71 nm, pore depth Lp = 294.96 nm, Young's contact angle θ0 = 23° and porosity η = 0.66. The maximum heat flux qin,max increases with the increase of rp and the decrease of Lp and θ0. The present work presents a promising numerical method to optimize thermal management devices using complex micro-nano composite structures.

Study on the Heat Transfer Characteristics of an Ambient Air Vaporizer with Multi-Component Fluids

China’s LNG import volume in 2021 reached 121.356 million tons, which makes China the largest importer in the world. The ambient air vaporizer (AAV) for LNG vaporization is an ideal selection for minimizing the average monetary value of terminals and maximizing operating efficiency. However, the heat and mass transfer performance of real multi-component LNG is not the same as that of the pure component in AAV; what is more, deep cryogenic and multi-component characteristics of LNG could lead to the deterioration of heat-transfer performance, which may cause catastrophic consequences. Thus, this difficulty should be concerning and solved in its operation. Based on the law of conservation of energy and mass, a heat and mass transfer model was established that can calculate the coupled heat transfer from the LNG to the air-side of the AAV along its own length. Empirical correlations are proposed to predict some basic properties of the frost layer at the outside of the tube, where the internal fluid is seen as a pure component and a multi-component. The numerical results show that the root–mean–square error (RMS) of the frost thickness is 0.749 mm, and the RMS of the outlet fluid temperature is 2.06 K and 2.21 K in summer and winter, respectively. That is in good agreement with the experimental data in the previous literature. The results show that the length of the finned tube in the AAV affected by pure CH4 was increased by 42.5%; therefore, we recommend shortening the finned tube on the basis of safety to save costs. Compared to the pure components reference experiments, when the CH4 content of multi-component in five regions was 78.48–96.91%, it is found that the different varieties of thermodynamic dryness degree x within the two types of components is the key point for the distinct mechanisms of the heat transfer characteristics of the AAV. Additionally, compared to changing the design pressure and flow rate, it is found that varying the flow rate has a much greater impact on the heat and mass transfer performance of the AAV than changing its pressure. The calculation of the coupled heat and mass transfer of the AAV can provide a theoretical basis for subsequent engineering designs.

Influence of As-N Interstitial Complexes on Strain Generated in GaAsN Epilayers Grown by AP-MOVPE

This work presents an investigation of the fully strained GaAsN/GaAs heterostructures obtained by atmospheric pressure metalorganic vapor phase epitaxy, focusing on the analysis of the strain generated in the GaAsN epilayers and its correlation with the formation of split interstitial complexes (N-As)As. We analyzed strained GaAsN epilayers with nitrogen contents and thicknesses varying from 0.93 to 1.81% and 65 to 130 nm, respectively. The composition and thickness were determined by high resolution X-ray diffraction, and the strain was determined by Raman spectroscopy, while the N-bonding configurations were determined by X-ray photoelectron spectroscopy. We found that the strain generated in the GaAsN epilayers is mainly caused by a lattice mismatch with the GaAs substrate. This macroscopic strain is independent of the amount of (N-As)As interstitial defects, while the local strain, induced by an alloying effect, tends to decrease with an increasing ratio of (N-As)As interstitial defects to substitutional nitrogen atoms incorporated into an arsenic sublattice—NAs. Here, we show experimentally, for the first time, a correlation between the strain in the GaAsN epilayers, caused by an alloying effect determined by Raman spectroscopy, and the (N-As)As/NAs ratio estimated by the XPS method. We found out that the (N-As)As interstitials compensate the local strain resulting from the presence of N in the GaAs matrix, if their amount does not exceed ~65% of the substitutional introduced nitrogen NAs.

Effects of Stepped Heating on the Initial Growth of Oxide Scales on NiCrAlHf Bond Coat Alloy under Air and Water Vapor Atmospheres.

Temperature and atmosphere have a significant effect on the oxidation of MCrAlY (M = Ni, Co) bond coating. The initial growth behavior of the NiCrAlHf bond coat alloy was investigated at 1100 °C under different atmospheric conditions and using heating methods. A thick Al2O3 oxide layer and large HfO2 particles were observed, perhaps due to metastable oxide growth at low temperatures when using stepped heating. However, in air and water vapor atmospheres, the oxide scale was thinner and the HfO2 precipitates were smaller in stepped heating than in constant heating. The size and distribution of the HfO2 particles might have induced different microstructures, particularly voids within the oxide scale.

Monolayer MoS2 of high mobility grown on SiO2 substrate by two-step chemical vapor deposition

We report a novel two-step ambient pressure chemical vapor deposition (CVD) pathway to grow high-quality MoS2 monolayer on the SiO2 substrate with large crystal size up to 110 μm. The large specific surface area of the pre-synthesized MoO3 flakes on the mica substrate compared to MoO3 powder could dramatically reduce the consumption of the Mo source. The electronic information inferred from the four-probe scanning tunneling microscope (4P-STM) image explains the threshold voltage variations and the n-type behavior observed in the two-terminal transport measurements. Furthermore, the direct van der Pauw transport also confirms its relatively high carrier mobility. Our study provides a reliable method to synthesize high-quality MoS2 monolayer, which is confirmed by the direct 4P-STM measurement results. Such methodology is a key step toward the large-scale growth of transition metal dichalcogenides (TMDs) on the SiO2 substrate and is essential to further development of the TMDs-related integrated devices.

Do 2 H and 18 O in leaf water reflect environmental drivers differently?

SummaryWe compiled hydrogen and oxygen stable isotope compositions (δ2H and δ18O) of leaf water from multiple biomes to examine variations with environmental drivers. Leaf water δ2H was more closely correlated with δ2H of xylem water or atmospheric vapour, whereas leaf water δ18O was more closely correlated with air relative humidity. This resulted from the larger proportional range for δ2H of meteoric waters relative to the extent of leaf water evaporative enrichment compared with δ18O. We next expressed leaf water as isotopic enrichment above xylem water (Δ2H and Δ18O) to remove the impact of xylem water isotopic variation. For Δ2H, leaf water still correlated with atmospheric vapour, whereas Δ18O showed no such correlation. This was explained by covariance between air relative humidity and the Δ18O of atmospheric vapour. This is consistent with a previously observed diurnal correlation between air relative humidity and the deuterium excess of atmospheric vapour across a range of ecosystems. We conclude that 2H and 18O in leaf water do indeed reflect the balance of environmental drivers differently; our results have implications for understanding isotopic effects associated with water cycling in terrestrial ecosystems and for inferring environmental change from isotopic biomarkers that act as proxies for leaf water.