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PubMed2002

Use of inverse gas chromatography to characterize cotton fabrics and their interactions with fragrance molecules at controlled relative humidity.

The present work focused on the surface characterization and fragrance interactions of a common cotton towel at different relative humidities (RHs) using inverse gas chromatography (IGC) and dynamic vapour sorption. The sigmoidal water sorption isotherms showed a maximum of 16% (w/w) water uptake with limited swelling at 100% RH. This means that water interacts strongly with cotton and might change its initial physico-chemical properties. The same cotton towel was then packed in a glass column and characterized by IGC at different relative humidities, calculating the dispersive and specific surface energy components. The dispersive component of the surface energy decreases slightly as a function of relative humidity (42 mJ/m2 at 0% RH to 36 mJ/m2 at 80% RH) which would be expected from swelling of the humidified cotton. The Gutmann's donor constant Kd increased from 0.28 kJ/mol at 0% RH to 0.42 kJ/mol at 80% RH, indicating that a greater hydrophilic surface exists at 80% RH, which is also as expected. Water, undecane and four fragrance molecules (dimetol, benzyl acetate, decanal and phenylethanol) were used to investigate cotton-fragrance interactions between 0 and 80% RH. The adsorption enthalpies and the Henry's constants were calculated and are discussed. The higher values for the adsorption enthalpies of polar molecules such as dimetol and phenylethanol suggest the presence of hydrogen bonds as the main adsorption mechanism. The Henry's constant of dimetol was also determined by headspace gas chromatography measurements at 20% RH, giving a similar value (230 nmol/Pa g by IGC and 130 nmol/Pa g by headspace GC), supporting the usefulness of IGC for such determinations. This work confirms the usefulness of chromatographic methods to investigate biopolymers such as textiles, starches and hairs.

Chromatography, Gas↗

PubMed2003

Change in secondary structure of silk fibroin during preparation of its microspheres by spray-drying and exposure to humid atmosphere.

Silk microspheres prepared by spray-drying were exposed to humid atmosphere (89% relative humidity, RH). Change in the secondary structure of silk fibroin during preparation of silk microspheres and exposure to high humidity was studied. Scoured silk fiber was dissolved in an aqueous solution of calcium chloride mixed with ethanol. After dialysis against purified water, theophylline was added to the solution as a model drug. Silk microspheres were obtained by spray-drying. Silk fibroin and theophylline were found to be amorphous in the microsphere by means of powder X-ray diffractometry. Fibroin assumed a beta-sheet conformation in the scoured silk fiber while it has an irregular structure in the microsphere, according to FTIR and Raman spectra. Fibroin recrystallized and its secondary structure changed to beta-sheet conformation by exposure of the microspheres to an atmosphere of 89% RH.

Fibroins↗

PubMed1999

The effects of temperature and humidity on the off-host survival of Psoroptes ovis and Psoroptes cuniculi.

The effects of both temperature and humidity on the survival of the mites Psoroptes ovis and Psoroptes cuniculi were considered in laboratory assays. When P. ovis and P. cuniculi were maintained at 95% humidity, maximum survival decreased linearly with increasing temperature, from approximately 15 days at 9 degrees C to 5 days at 30 degrees C. There was no significant difference between P. ovis and P. cuniculi in the effects of temperature on maximum survival. Adult male P. ovis and P. cuniculi had lower mean maximum survival than any of the other life cycle stages. There was a small but significant effect of humidity on survival for P. cuniculi; LT50 values were greater at 75-85% r.h. than at 55-65% r.h. The influence of off-host survival and the infestation of naive sheep from mites in the environment on the epidemiology of sheep scab are discussed.

Animals↗

PubMed1998

Hydrophilic membrane-based humidity control.

A dehumidification system for low gravity plant growth experiments requires the generation of no free-liquid condensate and the recovery of water for reuse. In the systems discussed in this paper, the membrane is a barrier between the humid air phase and a liquid-coolant water phase. The coolant water temperature combined with a transmembrane pressure differential establishes a water flux from the humid air into the coolant water. Building on the work of others, we directly compared different hydrophilic membranes for humidity control. In a direct comparison of the hydrophilic membranes, hollow fiber cellulose ester membranes were superior to metal and ceramic membranes in the categories of condensation flux per surface area, ease of start-up, and stability. However, cellulose ester membranes were inferior to metal membranes in one significant category, durability. Dehumidification systems using mixed cellulose ester membranes failed after operational times of only hours to days. We propose that the ratio of fluid surface area to membrane material area (approximately = membrane porosity) controls the relative performances among membranes. In addition, we clarified design equations for operational parameters such as the transmembrane pressure differential. This technology has several potential benefits related to earth environmental issues including the minimization of airborne pathogen release and higher energy efficiency in air conditioning equipment. Utilizing these study results, we designed, constructed, and flew on the space shuttle missions a membrane-based dehumidification system for a plant growth chamber.

Air Conditioning↗

PubMed2003

Upper airway irritation of terpene/ozone oxidation products (TOPS). Dependence on reaction time, relative humidity and initial ozone concentration.

Recently, we reported the formation of unidentified strong upper airway irritants in reaction mixtures of terpenes and ozone. The identified products included aldehydes, ketones and carboxylic acids. Here we report the effects of variation of reaction time, relative humidity and initial ozone concentration on irritant formation in a flow reaction system using R-(+)-limonene and isoprene. Upper airway irritation was measured in mice as reduction of the respiratory rate. For both substances maximum irritation was observed for low humidity (<2% RH)/short time (16-30 s) reaction mixtures, and both moderate humidity ( approximately 32% RH) and longer reaction times (60-90 s) resulted in significantly less irritation. These results suggest that some unidentified intermediates react with water vapor to give less irritating products. Irritation measured at four ozone concentrations (0.5, 1, 2 and 3.5 ppm) using low humidity/short time reaction conditions for limonene (50 ppm) and isoprene (500 ppm) revealed that at 0.5 ppm, irritation was at the same level as that for the pure terpenes, indicating that at 0.5 ppm ozone the combined irritant effect was near the no effect level for the product mixture.

Animals↗

PubMed1986

The survival of Escherichia coli in an aerosol at air temperatures of 15 and 30 degrees C and a range of humidities.

The survival of Escherichia coli in an aerosol was studied at several temperatures and over a range of relative humidities using a Henderson apparatus. Death occurred in two phases, the first lasting approximately 1 min; in the second the number of viable microorganisms declined exponentially. E. coli was robust and remained viable for many hours. Death was most rapid at low humidities (less than 50% r.h.) at 15 and 30 degrees C, with half-lives of 14 and 3 min respectively. In humid conditions the half-lives were much longer, approximately 83 and 14 min respectively. Based on this work, preliminary recommendations for the climate of livestock buildings can now be given to control the airborne spread of E. coli.

Air Microbiology↗

PubMed1995

Near-infrared measurement of relative and absolute humidity through detection of water adsorbed on a silica gel layer.

Near-IR spectroscopy is especially well suited to moisture determination because of the relatively high absorptivity of water compared to most other substances. In the present work, near-IR diffuse-transmittance spectroscopy is applied to the measurement of humidity via observation of adsorbed water on a high-performance thin-layer chromatography silica gel plate. The adsorbed water is detected through both ordinary absorption of radiation by water molecules and the increased scattering of near-IR radiation by the silica gel as it adsorbs more water. This technique shows promise as a highly accurate and sensitive humidity sensor with a time constant of less than 1 min. The addition of inorganic salts to the silica gel layer is shown to increase the response to water vapor. However, it also increases the time constant of the sensor. A miniature humidity sensor using a commercially available near-IR transmissive switch is also demonstrated. Possible interferences and hysteresis effects are investigated.

Adsorption↗

PubMed1999

Effect of temperature and humidity on the formation of dibutylurea in benlate fungicide.

Benomyl [methyl 1-(butylcarbamoyl)-2-benzimidazolecarbamate] is the active ingredient in DuPont Benlate fungicides. The formation of N, N'-dibutylurea (DBU), a phytotoxic degradation product of benomyl, in Benlate formulations was evaluated by analyzing Benlate samples maintained under simulated storage conditions and assessing the effects of temperature and humidity on sample moisture content, benomyl degradation, and the rate of DBU formation. Benomyl degraded during storage by the elimination of n-butylisocyanate (BIC) to form methyl 2-benzimidazole carbamate (MBC; carbendazim). Liberated BIC could then proceed to react with water to form DBU (first-order rate constant of 8.4 x 10(-)(4) s (-)(1)). The degradation of benomyl and subsequent formation of DBU were dependent on the temperature and highly dependent on the humidity of the storage environment. At the lower humidity storage conditions the rates of DBU formation were significantly higher in the dry flowable (DF) formulation than in the wettable powder (WP) formulation. The initial moisture content of Benlate DF samples was higher than those of Benlate WP samples, although the Benlate WP samples absorbed more moisture upon incubation. These results may yield insight on the appearance of high levels of DBU found in some boxes and bags of Benlate DF and Benlate WP formulations.

Benomyl↗

PubMed1999

Surfactant effects on cuticular penetration of neutral polar compounds: dependence on humidity and temperature.

Effects of poly(ethylene glycol) (PEG 400) and polydisperse fatty alcohol ethoxylates ("Genapols") on methylglucose penetration across cuticles of Pyrus communis were studied under different humidities and temperatures. All surfactants increased methylglucose penetration better than PEG 400. The efficacy was proportional to their own penetration. Genapol C-100 (C12.5E8.4; C, average number of carbon atoms in the alkyl chain; E, average number of ethoxy groups) effects were strongly concentration dependent (0.2-5 g/L). At 2 g/L distinct differences between surfactants were observed. Effects of Genapol C-050 (C12.5E5.8) did not depend on humidity (11-93% RH) and temperature (15-35 degrees C). They were maximal after application but decreased rapidly due to surfactant penetration. Genapol C-200 (C12.5E17) effects increased strongly with humidity and temperature both of which prevented its solidification. Genapol C-100 was superior under most conditions and never failed to increase penetration. There was no simple relationship between ethylene oxide content and surfactant effect.

Fatty Alcohols↗

PubMed1999

Dependence of the entomopathogenic fungus, Beauveria bassiana, on high humidity for infection of Rhodnius prolixus.

The impact of relative humidity (RH) on the infective potential of the isolate Bb INRA 297 of Beauveria bassiana (Bals.) Vuillemin (Deuteromycotina: Hyphomycetes) against first instar nymphs of Rhodnius prolixus Stål. (Hemiptera: Reduviidae) was determined. Fungus-treated insects were exposed to RHs ranged from 75 to 100% at 25 degrees C. Results clearly showed a threshold of humidity at ca. 96% for high and rapid mortality. After initial exposure to increasing periods of 97% (4, 8, 16, 24, 36 and 48 h) and subsequent transfer to constant lower RHs (43, 53, 75 and 86%) at a constant 25 degrees C, an incubation of at least 48 h at 97% RH was necessary to kill all insects. On changing RHs of 97/75% and different regimes of temperature (15/28 degrees C, 20/25 degrees C, 25/28 degrees C, and 25/35 degrees C), at least 72 h of initial exposure at 97% RH for the 15/28 degrees C regime, 48 h for the 20 degrees/25 degrees C and 25/28 degrees C regimes and 36 h for 25/35 degrees C were needed to kill all insects over a 6-day incubation time. Delayed exposure to favorable moisture condition (97% RH), significantly affected infection for up to a 3-day delay within the various temperature-humidity regimes tested.

Animals↗

PubMed1987

Water vapor sorption of water-soluble substances: studies of crystalline solids below their critical relative humidities.

Water vapor sorption on unground and ground samples of sodium chloride and sodium salicylate at relative humidities below RHo, that at which deliquescence is initiated, has been measured. Sorption isotherms, expressed as the amount sorbed per unit area of solid surface, were different for unground and ground samples. Measurement of specific surface area for samples previously exposed to various relative humidities revealed no change with unground samples but a significant reduction with ground samples beyond about 20% relative humidity. Correcting isotherms for this change in area brings the results with ground and unground samples into closer agreement. These studies reveal that relatively low levels of water vapor sorption on crystalline water-soluble solids, below RHo, can give rise to some form of "surface dissolution" when the solid had been subjected to various forms of mechanical disturbance.

Absorption↗

PubMed2001

Effects of humidity on reproductive behavior in male and female zebra finches (Taeniopygia guttata).

Zebra finches (Taeniopygia guttata) are regarded as opportunistic breeders with reproductive behaviors mediated by short-term proximal environmental conditions. This article provides experimental evidence for the role of humidity in reproductive behaviors. Zebra finches were subjected to experimentally manipulated high levels of relative humidity. Males gathered more nest material and sang more. Females showed no relationship between humidity and gathering nest materials, egg laying, or changes in rates of vocalization.

Animals↗

PubMed2001

Development rates of two Xenopsylla flea species in relation to air temperature and humidity.

The rate of development of immature fleas, Xenopsylla conformis Wagner and Xenopsylla ramesis Rothschild (Siphonaptera: Xenopsyllidae) was studied in the laboratory at 25 degrees C and 28 degrees C with 40, 55, 75 and 92% relative humidity (RH). These fleas are separately associated with the host jird Meriones crassus Sundevall in different microhabitats of the Ramon erosion cirque, Negev Highlands, Israel. This study of basic climatic factors in relation to flea bionomics provides the basis for ecological investigations to interpret reasons for paratopic local distributions of these two species of congeneric fleas on the same host. Both air temperature and RH were positively correlated with duration of egg and larval stages in both species. Change of humidity between egg and larval environments did not affect duration of larval development at any temperature. At each temperature and RH, the eggs and larvae of X. ramesis did not differ between males and females in the duration of their development, whereas female eggs and larvae of X. conformis usually developed significantly faster than those of males. For both species, male pupae developed slower than female pupae at the same air temperature and RH. Air temperature, but not RH, affected the duration of pupal development. At each humidity, duration of the pupal stage was significantly longer at 25 degrees C than at 28 degrees C: 15.3+/-1.7 vs. 11.7+/-1.2 days in X. conformis; 14.1+/-2.0 vs. 11.5+/-1.7 days in X. ramesis, with a significantly shorter pupal period of the latter species at 25 degrees C. These limited interspecific bionomic contrasts in relation to basic climatic factors appear insufficient to explain the differential habitat distributions of X. conformis and X. ramesis.

Animals↗

PubMed1999

Whole-body pre-cooling and heat storage during self-paced cycling performance in warm humid conditions.

The aim of this study was to establish the effect that pre-cooling the skin without a concomitant reduction in core temperature has on subsequent self-paced cycling performance under warm humid (31 degrees C and 60% relative humidity) conditions. Seven moderately trained males performed a 30 min self-paced cycling trial on two separate occasions. The conditions were counterbalanced as control or whole-body pre-cooling by water immersion so that resting skin temperature was reduced by approximately 5-6 degrees C. After pre-cooling, mean skin temperature was lower throughout exercise and rectal temperature was lower (P < 0.05) between 15 and 25 min of exercise. Consequently, heat storage increased (P < 0.003) from 84.0+/-8.8 W x m(-2) to 153+/-13.1 W x m(-2) (mean +/- s(mean)) after pre-cooling, while total body sweat fell from 1.7+/-0.1 l x h(-1) to 1.2+/-0.1 l h(-1) (P < 0.05). The distance cycled increased from 14.9+/-0.8 to 15.8+/-0.7 km (P < 0.05) after pre-cooling. The results indicate that skin pre-cooling in the absence of a reduced rectal temperature is effective in reducing thermal strain and increasing the distance cycled in 30 min under warm humid conditions.

Adolescent↗

PubMed2000

Aerosol light scattering measurements as a function of relative humidity.

The hygroscopic nature of atmospheric fine aerosol was investigated at a rural site in the Great Smoky Mountains National Park during July and August 1995. Passing the sample aerosol through an inlet, which housed an array of Perma Pure diffusion dryers, controlled the sample aerosol's relative humidity (RH). After conditioning the aerosol sample in the inlet, the light scattering coefficient and the aerosol size distribution were simultaneously measured. During this study, the conditioned aerosol's humidity ranged between 5% < RH < 95%. Aerosol response curves were produced using the ratio bspw/bspd; where bspw is the scattering coefficient measured at some RH greater than 20% and bspd is the scattering coefficient of the "dry" aerosol. For this work, any sample RH values below 15% were considered dry. Results of this investigation showed that the light scattering ratio increased continuously and smoothly over the entire range of relative humidity. The magnitude of the ratio at a particular RH value, however, varied considerably in time, particularly for RH values greater than approximately 60%. Curves of the scattering coefficient ratios as a function of RH were generated for each day and compared to the average 12-hour chemical composition of the aerosol. This comparison showed that for any particular RH value the ratio was highest during time periods of high sulfate concentrations and lowest during time periods of high soil or high organic carbon concentrations.

Aerosols↗

PubMed1980

A comparison of heat stress indices in a hot-humid environment.

The results of a study of nine physically fit young men performing moderate exercise under various levels of hot-humid conditions are reported. Environmental stress and physiological strain data from the total of 72 test sessions were collected and computed in terms of heat stress and heat strain indices. Single and multiple factor correlation coefficients were calculated on the basis of 11 stress indices versus 4 strain indices. Most of the empirical heat stress indices correlated best with the mean skin temperature, whereas the rational indices correlated best with heart rate and sweat loss. Because of its ease of use, the WGT or the CET index may be the best choice for preliminary industrial surveys in hot-humid environments. A simple and convenient nomogram was developed on the basis of the test data relating increase in heart rate to temperature, humidity, and air velocity.

Adult↗

PubMed1989

"Worst case" aerosol testing parameters: II. Efficiency dependence of commercial respirator filters on humidity pretreatment.

Previous studies have shown that relative humidity has a degrading effect on the performance of commercially available particulate air-purifying respirator filters. That degradation results from a reduction of charge within the filter. This study was done to evaluate the time-dependent effects of relative humidity pretreatment and the reduction of charge on filter penetration against a most penetrating, "worst case" aerosol challenge. Filters of the dust and mist; dust, fume, and mist; paint, lacquer, and enamel mist; and high efficiency types were tested after being pretreated in an environment of 38 degrees C and 85% relative humidity for periods up to 42 days. After various intervals of pretreatment (1, 7, 14, 28, and 42 days), the filters were tested against neutralized worst-case sodium chloride (NaCl) and dioctyl phthalate (DOP) aerosols for percent penetration. The results showed a drop in filter efficiency of approximately 2%-6% depending on preconditioning time, except for the high efficiency filters tested which showed no detectable change.

Aerosols↗

PubMed2001

Effect of relative humidity on mixed aerosols in atmosphere.

In this study, the effects of relative humidity on the deliquescent point and size of internally mixed aerosols diameter, NH4NO3 and (NH4)2SO4 were investigated using a Tandem Differential Mobility Analyzer (TDMA) with a relative humidity conditioner. The growth of mixed aerosols appears to have two deliquescent steps. The first one was at about 61.2-61.3%, but the second one was at around 77-78%. At the first deliquescence point, growth ratio at phase change was 7.5%, which agrees with the growth ratio of ammonium nitrate aerosol. Growth ratio of phase change at the second deliquescence point was about 20%, lower than the growth ratio of ammonium sulfate aerosol. In the relative humidity range of 80-85%, the growth ratio of the mixed aerosols reached 60%. In other words, it appears that growth ratio increases with the size of aerosol. Furthermore, a theoretical growth model of mixed aerosols was developed and applied to estimate the amount of composition of the mixed aerosols dissolved at each deliquescence point. The results also show that some of ammonium sulfate already dissolved at the first deliquescence point according to the theoretical growth model.

Aerosols↗