Changes In Atmospheric Relative Humidity Research Articles

Influence of relative humidity on the structure, swelling and electrical conductivity of PEDOT:PSS fibers

PEDOT:PSS is a conducting polymer with a wide variety of applications in the field of organic electronics. Over the past few years our group has developed PEDOT:PSS fibers with high electrical conductivity and robust mechanical properties, and we have observed changes in their properties that seemed to stem from seasonal changes in atmospheric relative humidity. In this work, we report the influence of relative humidity on the swelling, electrical conductivity and structure of wet-spun PEDOT:PSS fibers. The diameter of the fibers linearly increased with relative humidity up to the 70–80% range where the increase became exponential. The electrical conductivity reversibly decreased with increasing relative humidity with a similar linear and then exponential behavior. Additionally, an irreversible decrease (aging) in electrical conductivity was also observed. To gain more insight into the structural origin of these changes, wide angle x-ray scattering of the PEDOT:PSS fibers were gathered at different relative humidities in the 10–90% range so that the changes in structure could be observed in situ. On one hand, the lamella stacking distance of PEDOT and PSS chains increased linearly up to the 70–80% relative humidity range where the increase became exponential. On the other hand, the π-π stacking distance between PEDOT chains remained unaltered. We found that the changes in the lamella stacking distance were closely correlated to the changes observed for the diameter and electrical conductivity.

The Unusual Photochromic and Hydrochromic Switching Behavior of Cellulose-Embedded 1,8-Naphthalimide-Viologen Derivatives in the Solid-State.

Stimuli-responsive chromic materials such as photochromics, hydrochromics, thermochromics, and electrochromics have a long history of capturing the attention of scientists due to their potential industrial applications and novelty in popular culture. However, hybrid chromic materials that combine two or more stimuli-triggered color changing properties are not so well known. Herein, we report a design strategy that has led to a series of emissive 1,8-naphthalimide-viologen dyads which exhibit unusual dual photochromic and hydrochromic switching behavior in the solid-state when embedded in a cellulose matrix. This behavior manifests as reversible solid state fluorescence hydrochromism upon changes in atmospheric relative humidity (RH), and reversible solid state photochromism upon generation of a cellulose-stabilized viologen radical cation. In this design strategy, the bipyridinium unit serves as both a water-sensitive receptor for the hydrochromic fluorophore-receptor system, and a photochromic group, capable of eliciting its own visible colorimetric response, generating a fluorescence quenching radical cation with prolonged exposure to ultraviolet (UV) light. These dyes can be inkjet-printed onto cellulose paper or drop-cast as cellulose powder-based films and can be unidirectionally cycled between three different states which can be characteristically visualized under UV light or visible light. The material's photochromism, hydrochromism, and underlying mechanism of action was investigated using computational analysis, dynamic vapor sorption/desorption isotherms, electron paramagnetic resonance spectroscopy, and variable humidity UV-Vis adsorption and fluorescence spectroscopies.

The stomatal response to rising CO2 concentration and drought is predicted by a hydraulic trait-based optimization model.

Modeling stomatal control is critical for predicting forest responses to the changing environment and hence the global water and carbon cycles. A trait-based stomatal control model that optimizes carbon gain while avoiding hydraulic risk has been shown to perform well in response to drought. However, the model's performance against changes in atmospheric CO2, which is rising rapidly due to human emissions, has yet to be evaluated. The present study tested the gain-risk model's ability to predict the stomatal response to CO2 concentration with potted water birch (Betula occidentalis Hook.) saplings in a growth chamber. The model's performance in predicting stomatal response to changes in atmospheric relative humidity and soil moisture was also assessed. The gain-risk model predicted the photosynthetic assimilation, transpiration rate and leaf xylem pressure under different CO2 concentrations, having a mean absolute percentage error (MAPE) of 25%. The model also predicted the responses to relative humidity and soil drought with a MAPE of 21.9% and 41.9%, respectively. Overall, the gain-risk model had an MAPE of 26.8% compared with the 37.5% MAPE obtained by a standard empirical model of stomatal conductance. Importantly, unlike empirical models, the optimization model relies on measurable physiological traits as inputs and performs well in predicting responses to novel environmental conditions without empirical corrections. Incorporating the optimization model in larger scale models has the potential for improving the simulation of water and carbon cycles.

The triple oxygen isotope composition of phytoliths as a proxy of continental atmospheric humidity: insights from climate chamber and climate transect calibrations

Abstract. Continental atmospheric relative humidity (RH) is a key climate parameter. Combined with atmospheric temperature, it allows us to estimate the concentration of atmospheric water vapor, which is one of the main components of the global water cycle and the most important gas contributing to the natural greenhouse effect. However, there is a lack of proxies suitable for reconstructing, in a quantitative way, past changes of continental atmospheric humidity. This reduces the possibility of making model–data comparisons necessary for the implementation of climate models. Over the past 10 years, analytical developments have enabled a few laboratories to reach sufficient precision for measuring the triple oxygen isotopes, expressed by the 17O-excess (17O-excess = ln (δ17O + 1) – 0.528 × ln (δ18O + 1)), in water, water vapor and minerals. The 17O-excess represents an alternative to deuterium-excess for investigating relative humidity conditions that prevail during water evaporation. Phytoliths are micrometric amorphous silica particles that form continuously in living plants. Phytolith morphological assemblages from soils and sediments are commonly used as past vegetation and hydrous stress indicators. In the present study, we examine whether changes in atmospheric RH imprint the 17O-excess of phytoliths in a measurable way and whether this imprint offers a potential for reconstructing past RH. For that purpose, we first monitored the 17O-excess evolution of soil water, grass leaf water and grass phytoliths in response to changes in RH (from 40 to 100 %) in a growth chamber experiment where transpiration reached a steady state. Decreasing RH from 80 to 40 % decreases the 17O-excess of phytoliths by 4.1 per meg/% as a result of kinetic fractionation of the leaf water subject to evaporation. In order to model with accuracy the triple oxygen isotope fractionation in play in plant water and in phytoliths we recommend direct and continuous measurements of the triple isotope composition of water vapor. Then, we measured the 17O-excess of 57 phytolith assemblages collected from top soils along a RH and vegetation transect in inter-tropical West and Central Africa. Although scattered, the 17O-excess of phytoliths decreases with RH by 3.4 per meg/%. The similarity of the trends observed in the growth chamber and nature supports that RH is an important control of 17O-excess of phytoliths in the natural environment. However, other parameters such as changes in the triple isotope composition of the soil water or phytolith origin in the plant may come into play. Assessment of these parameters through additional growth chambers experiments and field campaigns will bring us closer to an accurate proxy of changes in relative humidity.

Triple oxygen and hydrogen isotopes of gypsum hydration water for quantitative paleo-humidity reconstruction

Atmospheric relative humidity is an important parameter affecting vegetation yet paleo-humidity proxies are scarce and difficult to calibrate. Here we use triple oxygen (δ17O and δ18O) and hydrogen (δD) isotopes of structurally-bound gypsum hydration water (GHW) extracted from lacustrine gypsum to quantify past changes in atmospheric relative humidity. An evaporation isotope-mass-balance model is used together with Monte Carlo simulations to determine the range of climatological conditions that simultaneously satisfy the stable isotope results of GHW, and with statistically robust estimates of uncertainty. We apply this method to reconstruct the isotopic composition of paleo-waters of Lake Estanya (NE Spain) and changes in normalized atmospheric relative humidity (RHn) over the last glacial termination and Holocene (from ∼15 to 0.6 cal. kyrs BP). The isotopic record indicates the driest conditions occurred during the Younger Dryas (YD; ∼12–13 cal. kyrs BP). We estimate a RHn of ∼40–45% during the YD, which is ∼30–35% lower than today. Because of the southward displacement of the Polar Front to ∼42°N, it was both windier and drier during the YD than the Bølling–Allerød period and Holocene. Mean atmospheric moisture gradually increased from the Preboreal to Early Holocene (∼11 to 8 cal. kyrs BP, 50–60%), reaching 70–75% RHn from ∼7.5 cal. kyrs BP until present-day. We demonstrate that combining hydrogen and triple oxygen isotopes in GHW provides a powerful tool for quantitative estimates of past changes in relative humidity.

The interactive effect of root disease and climate on wood properties in halfsibling Douglas-fir families

Certain tree phenotypes enhance wood value properties and promote adaptation to climate extremes. However, the disciplines of wood science, physiology, and pathology rarely intersect to elucidate how survival, productivity, and wood property traits relate. Reaction to biotic and abiotic stress agents expressed in trees as disease resistance or tolerance were studied at the cell and tissue level. Five field-grown 21–22-year-old maternal halfsibling Douglas-fir Pseudotsuga menziesii var. glauca (Beissn.) Franco families were inoculated with Armillaria ostoyae (Romagn.) Herink to determine the interaction between disease, climate, and family on wood properties obtained from cores. The families originated from a lower elevation ecosystem and were categorized a priori as fungal disease resistant, tolerant or susceptible from a field study. Cell property changes suggestive of hydraulic adaptation to low precipitation were similar but lesser than the changes resulting from fungal root infection. The greatest increase in wood density occurred in disease resistant families after infection through a combination of thicker cell walls, smaller tracheid radial diameter, and reduced earlywood width. Microfibril angle and modulus of elasticity were affected differently with respect to changes in atmospheric relative humidity. Disease resistant compared to susceptible and tolerant families had inherent differences regardless of infection status. The sudden and localized changes in wood density associated with a disease resistance response could negatively impact on product quality, uniformity, and growth; on the other hand, denser wood and reduced growth associated with disease resistance may enhance drought survival. Understanding the interaction of these traits is important for adaptation to environmental stressors.

Alistair M. Hetherington.

Alistair M. Hetherington.

Rates and geochemical processes of soil and salt crust formation in Salars of the Atacama Desert, Chile

The hyperarid Atacama Desert contains numerous local basins with surficial salt crusts, known as salars, where evaporation of shallow groundwater drives the major soil processes. We examine chemical and isotopic profiles in two soils of differing ages from the Salar Llamara to determine the geochemical processes involved in their formation. Evaporation, which provides salts to the soils through mineral precipitation, decreases with increasing salt crust thickness, and average~0.03mmm−2d−1 over geological time frames. Salt distribution varies predictably with depth and soil age, with the most soluble compounds concentrated nearest to the land surface, indicating the direction of fluid flow. δ34S values of mineral sulfate tend to decrease with decreasing soil depth, following a pattern indicative of Rayleigh-like fractionation as solute-rich waters migrate toward the land surface. δ13C and δ18O values of carbonate suggest that the uppermost halite layers, which contain very small amounts of carbonate, have a strong biological signature. In contrast, carbonate-rich layers deeper in the profiles consist of largely unmodified lacustrine carbonate that formed in highly evaporitic lake conditions. The continuous upward evaporation of water and dissolved solutes creates a rugged and physically dynamic halite crust composed of rounded salt nodules. The crust undergoes deliquescence as atmospheric relative humidity rises from marine air intrusions, and we found that the halite nodules on the surface of the Salar Llamara are nearly always at or above deliquescence relative humidity. The interiors of these nodules are therefore able to buffer the large diurnal changes in atmospheric relative humidity allowing for the survival of halophilic microbial communities in an otherwise very dry environment. Radiocarbon measurements of occluded organic C in the surface crusts indicate that C cycling occurs at differing rates depending on local micrometeorological conditions, and that a given salt crust feature may persist for thousands of years once formed.

Daily covariations in near-surface relative humidity and temperature over the ocean

[1] Changes in atmospheric relative humidity in concert with temperature changes in a future climate may have large consequences for the water vapor feedback, the hydrological cycle, and its interaction with weather systems. This study contributes to the basic understanding of the relationship between temperature and humidity by investigating the processes leading to synoptic-scale covariations of the two variables close to the ocean surface. Daily data from in situ observations between 10°S and 50°N and global ERA-Interim reanalyses are used. Correlations between temperature and both specific and relative humidity are calculated. The results from the two data sets appear to be greatly consistent. They show strong anticorrelation between temperature and relative humidity (RH) in the inner tropics with minimum correlation coefficients below −0.8. In midlatitudes, there are large areas where the correlation coefficient of temperature and RH is positive and greater than 0.6. The anticorrelation in the tropics is found to be related to convective precipitation, which, on the one hand, leads to local temperature decrease due to vertical mixing and reduction of solar radiation by clouds. On the other hand, rainfall is associated with an increase in boundary layer RH. Over the midlatitude ocean, daily temperature variations are mainly controlled by meridional transport, as shown with the help of backward trajectories. Moreover, advection of cold air typically goes along with vertical moisture transport, either due to large-scale subsidence or turbulent mixing, causing a reduction of near-surface RH. All together, this dynamical effect induces the positive temperature-RH correlation.

The virtual and physical preparation of the Collard plesiosaur from Bridgwater Bay, Somerset, UK

The 'Collard Plesiosaur', found in 2003 in Bridgwater Bay on the Somerset coast is the only complete and fully articulated plesiosaur skeleton to have been found in Britain for over 100 years. The 1.5 metre long specimen was preserved in the finegrained and thinly laminated Lower Liassic Kilve Shales. This lithology is susceptible to fluctuations in humidity, severely compromising the integrity of specimens once dry. The priorities for the project were to arrest shale delamination caused by environmental fluctuations and to prepare the specimen for research. The specimen appeared to be mostly well fossilised in a homogeneous, un-cemented matrix, offering excellent potential for non-destructive recovery of fossil information using conventional X-radiography and Computed Tomography before the preparation commenced. Despite the skeleton being variably mineralised, the analyses yielded very detailed images. This 'virtual preparation' helped to inform the subsequent physical preparation, with the conventional radiographs proving most useful. In addition, the project demonstrated that such analyses are not just useful for guiding preparation but also for recording material that might be removed during preparation and highlighting details not visible to the naked eye or that remain buried. During preparation, experimental attempts to consolidate matrix samples were unsuccessful - the shale layers distorted and delaminated. However, the adhesive Paraloid B72 was successfully applied to the sides of the specimen blocks in liberal quantities, providing a useful partial barrier to future changes in atmospheric relative humidity. Scalpels were found to be the most appropriate tools for preparing the specimen, removing one paper-thin layer of shale at a time.

EXE: a Climatically Sensitive Model to Study Climate Change and CO2 Enhancement Effects on Forests

Vegetation plays a significant role in determining the local and regional hydrology of ice-free continental surfaces and the dynamics of the atmosphere above it. Vegetation also influences the global climate directly by affecting atmospheric chemistry. In particular, it partially controls the carbon cycle. In turn, vegetation is influenced by climate and changes in the ambient concentration of CO2. This may have important consequences for agriculture and natural resource exploitation. A formal recognition of atmosphere/biosphere interrelationships is crucial but insufficient. Systematic investigations of the interactions between climate, plant physiology and ecology are badly needed. In this spirit, this paper presents the results of numerical simulations performed with the Energy, water and momentum eXchange, and Ecological dynamics (EXE) model at a local scale over periods of 400-800 (simulation) years. EXE constitutes a first attempt to couple a physiologically based water budget and an explicit treatment of ecological dynamics. In principle, EXE could be forced by the output of an atmospheric general circulation model (GCM). Within this context, the paper demonstrates through the examples it analyses that both potential stomata1 response to CO2 and the possible range of changes in atmospheric relative humidity are likely major factors in determining the ecosystem response to greenhouse warming. Consequently, they should be considered in future studies of this kind. The paper also provides explanations regarding the movement of ecotones, defined as the transition zones between different vegetation assemblages. Taking the North American forest/prairie boundary as a case study, the analysis of the results shows how, in a greenhouse warmed world, St Paul, MN, might look like North Platte, NE. Finally, building on the previous example by using two different models, this study illustrates that results can be strongly model dependent and encourages extreme caution in their interpretation.

Influence of relative humidity on germination and disease development in Erysiphe graminis

The effect of relative humidity during production and germination of conidia of Erysiphe graminis f.sp. hordei was examined in the laboratory. High humidities at both stages promoted the infectivity of the conidia. Experiments with different soil depths showed that deeper soils resulted in higher humidities around the plants and significantly greater levels of disease. When differential humidity build-up around the plants during different watering regimes was prevented there was no significant difference in disease development. This confirms that the effects observed were due to changes in atmospheric relative humidity, not to alterations in the water supply to the host plant.

Cotton boll mycoflora from Sudan

Flower pedicels, more contaminated with moulds than cotton boll apices, contributed to the infection of the cellulose-rich locks. Similar to the total number of contaminants recovered from all boll segments, locks mycoflora was also significantly enhanced with boll age. Number of isolates from Gezira consistently conformed with changes in atmospheric relative humidity attaining a maximum in the 4th week following flower opening. Locks from the relatively dry and hot Shambat area exhibited an inconsistent mycofloral development although they collected 6.3% more infection than those picked from Gezira. An insignificant correlation between boll age and either pedicel or boll apex ifection was recorded. The relatively humid Gezira not only stimulated greater mould isolates (49.4% over Shambat's), but provided for 52.3% more infected boll apices over Shambat's. Twenty fungal genera and species, 90% of which were cellulolytic (2), were recovered from 1–7 week-old green bolls. Aspergillus nidulans and Cladosporium herbarum unintermittently persisted throughout the sampling duration. Abundance of these two contaminants insignificantly matched with either boll age or sampling area. Eurotium was first record to native lint.