Function Of Ambient Relative Humidity Research Articles

Temporally Anticorrelated Subdiffusion in Water Nanofilms on Silica Suggests Near-Surface Viscoelasticity.

Single-molecule tracking was used to probe the local rheology of interfacial water. Fluorescent rhodamine molecules were tracked on silica surfaces as a function of ambient relative humidity, which controlled the thickness of condensed water nanofilms. At low humidity, the molecules exhibited confined diffusion in the vicinity of isolated adsorption sites characterized by a broad distribution of binding stiffness constants; subsequent chemical or physical surface passivation selectively eliminated stiffer binding sites. At increased humidity, molecularly thin water films condensed, permitting near-surface transport of rhodamine molecules. Motion was subdiffusive, with an anomalous exponent increasing with the nanofilm thickness. Molecular trajectories were temporally anticorrelated, ergodic, but also featured transient binding and intermittent diffusion. Statistical modeling demonstrated that this complex motion in water nanofilms had the characteristics of fractional Brownian motion combined with a continuous-time random walk. This was consistent with diffusion within viscoelastic nanofilms, suggesting persistent molecular structuring in the vicinity of the silica surface.

The physiology of Venezillo arizonicus: water balance and the cuticular water barrier

This study investigated the water balance physiology of Venezillo arizonicus, a land isopod endemic to the Southwest Desert Ecoregion of North America. Evaporative water losses were measured in two ways: gravimetric in dry air, and by perfusing animals with dry air in a respirometry chamber and monitoring downstream relative humidity (RH). The respective mean loss flux estimates were 0.140 and 0.177 μg h−1 cm−2 Pa−1, lower than other N. American Oniscidea described to date (≥0.491 μg h−1 cm−2 Pa−1). Humidity monitoring revealed intermittent sharp peaks in RH, attributed to the release of maxillary urine. Whole-animal flux increased as a function of temperature, with a critical temperature (Tc) between 38 and 42 °C identifiable by a clear Arrhenius break point. Hexane-rinsed whole animals yielded straight-chain, saturated hydrocarbons (C21–C33). The surface density of extracted alkanes (0.64 µg cm−2) was somewhat higher than previously determined values for mesic species, although modest compared to insects and arachnids. Dehydrated animals exposed to high RH (>88%) demonstrated active water vapor absorption (WVA) like other Crinocheta, with an extrapolated uptake threshold of approximately 85% RH (Aw = 0.85), the lowest value reported for Oniscidea. The maximum uptake flux increased linearly as a function of ambient RH. Mass-specific uptake in 100% RH was 49% d−1, similar to values determined previously for Armadillidium vulgare and Porcellio scaber. The low WVA threshold of V. arizonicus, and the species’ low permeability, are consistent with its known range in the arid desert southwest and the desiccation stress of its typical aeolian sand and seasonal wash habitats.

Single-particle experiments measuring humidity and inorganic salt effects on gas-particle partitioning of butenedial

Abstract. An improved understanding of the fate and properties of atmospheric aerosol particles requires a detailed process-level understanding of fundamental factors influencing the aerosol, including partitioning of aerosol components between the gas and particle phases. Laboratory experiments with levitated particles provide a way to study fundamental aerosol processes over timescales relevant to the multiday lifetime of atmospheric aerosol particles, in a controlled environment in which various characteristics relevant to atmospheric aerosol can be prepared (e.g., high surface-to-volume ratio, highly concentrated or supersaturated solutions, changes to relative humidity). In this study, the four-carbon unsaturated compound butenedial, a dialdehyde produced by oxidation of aromatic compounds that undergoes hydration in the presence of water, was used as a model organic aerosol component to investigate different factors affecting gas–particle partitioning, including the role of lower-volatility “reservoir” species such as hydrates, timescales involved in equilibration between higher- and lower-volatility forms, and the effect of inorganic salts. The experimental approach was to use a laboratory system coupling particle levitation in an electrodynamic balance (EDB) with particle composition measurement via mass spectrometry (MS). In particular, by fitting measured evaporation rates to a kinetic model, the effective vapor pressure was determined for butenedial and compared under different experimental conditions, including as a function of ambient relative humidity and the presence of high concentrations of inorganic salts. Even under dry (RH<5 %) conditions, the evaporation rate of butenedial is orders of magnitude lower than what would be expected if butenedial existed purely as a dialdehyde in the particle, implying an equilibrium strongly favoring hydrated forms and the strong preference of certain dialdehyde compounds to remain in a hydrated form even under lower water content conditions. Butenedial exhibits a salting-out effect in the presence of sodium chloride and sodium sulfate, in contrast to glyoxal. The outcomes of these experiments are also helpful in guiding the design of future EDB-MS experiments.

Wintertime hygroscopic growth factors (HGFs) of accumulation mode particles and their linkage to chemical composition in a heavily polluted urban atmosphere of Kanpur at the Centre of IGP, India: Impact of ambient relative humidity

This study reported results of the wintertime simultaneous measurements of hygroscopic growth factors (HGFs) and particle-phase chemical composition of accumulation mode particles using a self-assembled Hygroscopic Tandem Differential Mobility Analyzer (H-TDMA) and an Aerodyne High-Resolution Time-of-Flight Aerosol Mass Spectrometer (HR-ToF-AMS), respectively at a heavily polluted urban atmosphere of Kanpur, situated in the center of IGP in India. HGFs at 85% relative humidity (RH) and the size-resolved composition of ambient aerosol particles (dry electrical mobility diameters of 100 and 150 nm) were investigated. HGF_85% was found to increase with particle size. The relative mass fraction of organic aerosol (OA) and NH4NO3 are probably the major contributors to the fluctuation of the HGF_85% for both particle sizes. The HGF_85% of accumulation mode particles were observed to increase from the minimum value observed during the morning until its maximum afternoon value. This study reported two maximum (early morning and afternoon time) and two minimum values (morning and evening time) of HGF_85%s. As a consequence, the main reasons for this incremental behavior were, increase in the ratio of inorganic to OA and oxidation level, f44 (m/z44/OA) of the OA within the particle phase. In context to the effect of ambient RH, this study reported two distinct variations of mean HGF_85% as the function of ambient RH. The positive linear relationship at low RH (LRH, RH ≤ 50%) was clearly associated with low OA loading, relatively higher substantial temperature, and wind speed. We also observed increment in f44, and effective density indicating aging of aerosol. However, HGF_85% was found to inversely decline as a function of RH at higher RH (HRH, RH > 50%) conditions, which clearly reflect the more significant contribution of primary OA and lower oxidation level of OA. Our results show the declining trend in size-resolved effective density at HRH conditions, confirming the above conclusions.

Development of a Suitable Physical Form for a Sphingosine-1-phosphate Receptor Agonist

AMG 369 (1), a novel S1P1 agonist, was selected for clinical development for the treatment of multiple sclerosis. Form B of the zwitterionic molecule was initially identified as a potential development form. However, because of the instability of the phase as a function of ambient relative humidity, investigations of other polymorphs of the zwitterion and basic and acidic salt screening were conducted to identify an acceptable physical form for long-term development. An HCl dihydrate, an unsolvated sulfate salt, a hexahydrate calcium salt, and a monohydrate of the zwitterion were identified as potentially viable phases. The quality attributes of these phases were then compared along with their propensity to undergo acid-promoted degradation.

A Blue Spectral Shift of the Hemoglobin Soret Band Correlates with the Age (Time Since Deposition) of Dried Bloodstains

The ability to determine the time since deposition of a bloodstain found at a crime scene could prove invaluable to law enforcement investigators, defining the time frame in which the individual depositing the evidence was present. Although various methods of accomplishing this have been proposed, none has gained widespread use due to poor time resolution and weak age correlation. We have developed a method for the estimation of the time since deposition (TSD) of dried bloodstains using UV-VIS spectrophotometric analysis of hemoglobin (Hb) that is based upon its characteristic oxidation chemistry. A detailed study of the Hb Soret band (λmax = 412 nm) in aged bloodstains revealed a blue shift (shift to shorter wavelength) as the age of the stain increases. The extent of this shift permits, for the first time, a distinction to be made between bloodstains that were deposited minutes, hours, days and weeks prior to recovery and analysis. The extent of the blue shift was found to be a function of ambient relative humidity and temperature. The method is extremely sensitive, requiring as little as a 1 µl dried bloodstain for analysis. We demonstrate that it might be possible to perform TSD measurements at the crime scene using a portable low-sample-volume spectrophotometer.

Sensitivities of the absorptive partitioning model of secondary organic aerosol formation to the inclusion of water

Abstract. The predicted distribution of semi-volatile organic components between the gaseous and condensed phase as a function of ambient relative humidity and the specific form of the partitioning model used has been investigated. A mole fraction based model, modified so as not to use molar mass in the calculation, was found to predict identical RH dependence of component partitioning to that predicted by the conventional mass-based partitioning model which uses a molar mass averaged according to the number of moles in the condensed phase. A recently reported third version of the partitioning model using individual component molar masses was shown to give significantly different results to the other two models. Further sensitivities to an assumed pre-existing particulate loading and to parameterised organic component non-ideality are explored and shown to contribute significantly to the variation in predicted secondary organic particulate loading.

Effect of Relative Humidity on the Viscoelastic and Mechanical Properties of Spray‐Dried Powder Compacts

Spray‐dried powder compacts exhibit viscoelastic properties such as stress relaxation, creep, and delayed elastic strain. This behavior is attributed to the organic binder, which forms bridges between the particles in spray‐dried granules, thereby affecting their deformation characteristics. The viscosity and distribution of the binder within the powder compact can affect its mechanical and viscoelastic properties. In this study, the powder was conditioned at different ambient relative humidity (RH) levels, to vary the binder viscosity. Load deformation, stress relaxation, fracture strength, and fracture toughness behavior of ferrite powder compacts were studied as a function of ambient RH both before and after compaction. The loading rate was found to significantly affect the time‐dependent response, and the relaxation times decreased at high humidity levels during compaction. It is proposed that increasing the humidity level during compaction increases the number of particle–particle contacts. This simple mechanism of binder redistribution led to slower relaxation times, increases in fracture strength, and elastic modulus of the green bodies, without significantly altering the fracture toughness when powders were compacted at high humidity to a given density.

Cirrus cloud occurrence as function of ambient relative humidity: a comparison of observations obtained during the INCA experiment

Abstract. Based on in-situ observations performed during the Interhemispheric differences in cirrus properties from anthropogenic emissions (INCA) experiment, we introduce and discuss the cloud presence fraction (CPF) defined as the ratio between the number of data points determined to represent cloud at a given ambient relative humidity over ice (RHI) divided by the total number of data points at that value of RHI. The CPFs are measured with four different cloud probes. Within similar ranges of detected particle sizes and concentrations, it is shown that different cloud probes yield results that are in good agreement with each other. The CPFs taken at Southern Hemisphere (SH) and Northern Hemisphere (NH) midlatitudes differ from each other. Above ice saturation, clouds occurred more frequently during the NH campaign. Local minima in the CPF as a function of RHI are interpreted as a systematic underestimation of cloud presence when cloud particles become invisible to cloud probes. Based on this interpretation, we find that clouds during the SH campaign formed preferentially at RHIs between 140 and 155%, whereas clouds in the NH campaign formed at RHIs somewhat below 130%. The data show that interstitial aerosol and ice particles coexist down to RHIs of 70-90%, demonstrating that the ability to distinguish between different particle types in cirrus conditions depends on the sensors used to probe the aerosol/cirrus system. Observed distributions of cloud water content differ only slightly between the NH and SH campaigns and seem to be only weakly, if at all, affected by the freezing aerosols.

Single Molecule Studies of Dynamics in Polymer Thin Films and at Surfaces: Effect of Ambient Relative Humidity

The temporal emission characteristics of nile red (NR) single molecules in and on hydrophilic and hydrophobic polymer films are studied as a function of ambient relative humidity (RH), and hence, the film hydration level. The materials studied include poly(vinyl alcohol) (PVA) and poly(methyl methacrylate) (PMMA). The temporal emission characteristics for NR in and on PVA are shown to be very sensitive to the ambient RH. Autocorrelation of the single-molecule fluorescence transients reveal signal fluctuations on two distinct time scales: 0.1−1 s and 1−2 ms. The fast fluctuations become slower and the slow fluctuations faster with increasing RH. In stark contrast, data obtained from NR in and on PMMA show these films to be almost completely insensitive to ambient moisture. These results point to the important role played by material hydrophilicity in the sensitivity of single-molecule experiments to RH variations. The chemical and physical origins of the RH-dependent signal fluctuations are explored in de...

Lateral Diffusion in Substrate-Supported Lipid Monolayers as a Function of Ambient Relative Humidity

We analyzed the influence of water activity on the lateral self-diffusion of supported phospholipid monolayers. Lipid monolayer membranes were supported by polysaccharide cushions (chitosan and agarose), or glass. A simple diffusion model was derived, based on activated diffusion with an activation energy, E a, which depends on the hydration state of the lipid headgroup. A crucial assumption of the derived model is that E a can be calculated assuming an exponential decay of the humidity-dependent disjoining pressure in the monolayer/substrate interface with respect to the equilibrium separation distance. A plot of ln( D) against ln( p 0 /p) , where D is the measured diffusion coefficient and p 0 and p are the partial water pressures at saturation and at a particular relative humidity, respectively, was observed to be linear in all cases (i.e., for differing lipids, lateral monolayer pressures, temperatures, and substrates), in accordance with the above-mentioned diffusion model. No indications for humidity-induced first-order phase transitions in the supported phospholipid monolayers were found. Many biological processes such as vesicle fusion and recognition processes involve dehydration/hydration cycles, and it can be expected that the water activity significantly affects the kinetics of these processes in a manner similar to that examined in the present work.

Relation between ambient humidity and ionic conductivity of poly(thionaphtheneindole): behaviour as an amperometric humidity sensor

The electrical characteristics of oxidized poly(thionaphtheneindole) were investigated as a function of ambient relative humidity (r.h.). The current flowing through a pressed pellet of material between two massive gold electrodes plotted against voltage gives a wave-shaped curve with a halfwave potential at V = ~3V. The current recorded at 4V (plateau of the wave) is a sigmoidal function of r.h. with the inflexion point at ~60%. An interpretation of these findings is given, based on the influence of water on the dielectric constant of the material and on acid–base equilibrium between poly(thionaphtheneindole) and water, from which protons are produced. The behaviour of poly (thionaphtheneindole) as the active component of an amperometric humidity sensor is also reported.

Hydrogen chloride vapor pressure over metal chloride aerosols from rocket exhausts

The importance of chloride coatings in determining the atmospheric properties of solid fuel exhaust particles is examined using a rigorous thermodynamic treatment of HC1-A1C1 3-H2O and HCl-BeCl2-H2O mixtures. Although chloride salts represent only about 5% of the mass of the particles, their hygroscopic nature means that they dominate the control of the liquid water content of exhaust clouds with low water vapor content. In the presence of chloride particles, liquid water and dissolved HC1 persist over a wider range of conditions than in a pure HC1-H2O cloud. An equilibrium model of HC1 partitioning in the Space Shuttle exhaust cloud satisfactorily represents the measured distributions and suggests that cloud lifetime is a function of ambient relative humidity. Beryllium chloride particles show similar properties to those of aluminum.

A noninvasive, in vivo technique to quantitatively measure water concentration of the stratum corneum using attenuated total-reflectance infrared spectroscopy.

In order to noninvasively measure water concentration in the stratum corneum, infrared spectra were obtained using an attenuated total-reflectance technique in conjunction with Fourier transform spectroscopy. A weak water-absorbance band near 2,100 cm-1 was detected in both in vivo and in vitro spectra. The significance of this band is that it occurs in a region of the mid-infrared where the stratum corneum and most topically applied substances show no absorbance. In vitro spectra obtained as a function of ambient relative humidity showed an increase in the absorbance near 2,100 cm-1 with increasing water concentration in the stratum corneum. The combined in vivo and in vitro results lead to a quantitative assessment of water concentration in the uppermost layers of the stratum corneum.