SEARCH · Search PubMed

Results for “Humidity”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 253 records · Page 14Linked to original sources

PubMed2003

Investigation of the influence of humidity on the ultrasonic agglomeration of submicron particles in diesel exhausts.

Removing very fine particles in the 0.01-1 micro m range generated in diesel combustion is important for air pollution abatement because of the impact such particles have on the environment. By forming larger particles, acoustic agglomeration of submicron particles is presented as a promising process for enhancing the efficiency of the current filtration systems for particle removal. Nevertheless, some authors have pointed out that acoustic agglomeration is much more efficient for larger particles than for smaller particles. This paper studies the effect of humidity on the acoustic agglomeration of diesel exhausts particles in the nanometer size range at 21 kHz. For the agglomeration tests, the experimental facility basically consists of a pilot scale plant with a diesel engine, an ultrasonic agglomeration chamber a dilution system, a nozzle atomizer, and an aerosol sampling and measuring station. The effect of the ultrasonic treatment, generated by a linear array of four high-power stepped-plate transducers on fumes at flow rates of 900 Nm(3)/h, was a small reduction in the number concentration of particles at the outlet of the chamber. However, the presence of humidity raised the agglomeration rate by decreasing the number particle concentration by up to 56%. A numerical study of the agglomeration process as a linear combination of the orthokinetic and hydrodynamic agglomeration coefficients resulting from mutual radiation pressure also found that acoustic agglomeration was enhanced by humidity. Both results confirm the benefit of using high-power ultrasound together with humidity to enhance the agglomeration of particles much smaller than 1 micro m.

Acoustics↗

PubMed1999

Effects of humidity and soil organic matter on the sorption of chlorinated methanes in synthetic humic-clay complexes.

Vapor-phase sorption is the most influential process governing the transport and the fate of volatile organic compounds in soil. To understand the influence of both soil organic content and the humidity of soil on the vapor sorption is an important process for degradation processes. The single-pellet moment technique was used to investigate sorption and diffusion of trichloromethane (TCM) and carbon tetrachloride (CTC) at varying relative humidities (0-80%) of synthetic humic-clay complex pellets consisting of clay (montmorillonite) and different amounts of organic matter (humic acid). The effective diffusivities of TCM and CTC did not show a noticeable change with moisture and humic acid content. On the other hand, with increasing humic acid content of clay at 0% relative humidity, an appreciable decrease of the equilibrium sorption constants of the tracers (TCM, CTC) was found because of the blockage of some sites of the mineral surfaces and especially micropores by the humic acid. The presence of water also reduced dramatically the sorption of TCM and CTC on synthetic humic-clay complexes. Above 20% relative humidity, the sorption coefficient of TCM and CTC varied only slightly with humic acid content. It was concluded that the sorption of TCM and CTC in synthetic humic-clay complexes was strongly effected by the moisture and humic acid content.

Adsorption↗

PubMed2001

HeatBalance, a computer program to determine optimum incubator air temperature and humidity. A comparison against nurse settings for infants less than 29 weeks gestation.

BACKGROUND: Very immature newborn infants need close control of their thermal environment. Decisions on incubator temperature and humidity settings can be difficult and available charts are not readily applicable to these babies. A computer program (HeatBalance) using basic principles to calculate heat gains and losses has been developed. The program recommends incubator temperature and humidity settings to keep babies in thermal balance. AIM: The aim of this study was to compare the effect of the program on temperature control of infants <29 weeks gestation with that achieved by experienced nurses. METHOD: Twenty consecutive babies were studied over the first 5 days of life, all nursed in incubators using air mode control. The first 10 had temperature and humidity set by the nurses while the next 10 had incubator settings determined by the program. Nurses could alter the parameters if the babies were too hot or cold. Incubator temperature and humidity data along with central and peripheral temperatures from the babies were collected autonomicallly onto a cotside computer system. RESULTS: There were no differences between the groups in mean central temperatures or the periods of time the babies were either too hot (central temperature T(c)>37.5) or too cold (T(c)<36.5). In the control group, the nurses often altered incubator temperature because of changes in the infant's temperature on the monitors. On each day of the study, the nurses deviated from the HeatBalance recommendations between 11% and 22% of the time. CONCLUSIONS: The HeatBalance program and the nurses achieved similar results in temperature stability for these immature infants. Whichever method was used to determine the initial incubator settings, this study highlighted the importance of continuous monitoring of central and peripheral temperatures in these infants.

Body Temperature Regulation↗

PubMed2002

Long-term stability of heat-humidity cured cellulose acetate phthalate coated beads.

The objective of this study was to investigate the influence of stability storage conditions on the enteric release of heat-humidity cured cellulose acetate phthalate (CAP) coated beads. Theophylline beads were coated with 25 or 35% diethyl phthalate plasticized CAP dispersion (Aquacoat CPD), and cured at a heat-humidity condition (50 degrees C/75% RH) for 24h. The cured beads were then stored in various container/closure systems (open glass containers, sealed glass containers with and without desiccant) and exposed to 40 degrees C/75% RH for 6 months or 25 degrees C/60% RH for 12 months. At accelerated conditions (40 degrees C/75% RH), only beads stored in sealed glass containers with desiccant displayed stable release profiles throughout the exposure period. The beads stored in sealed glass containers without desiccant showed increased theophylline release in acidic media at 2h, and did not maintain enteric resistance at 6 months. The release profiles of beads stored in open containers, directly exposed to 40 degrees C/75% RH, were the least stable. The decrease in enteric protection of the beads stored at these two packaging conditions was correlated to an increased phthalic acid content in the films. At ambient storage conditions (25 degrees C/60% RH), all samples possessed enteric release properties, irrespective of the container/closure system. Beads stored in sealed glass containers with desiccant remained the most stable compared to those at the other two packaging conditions. The results indicated that although humidity significantly contributed to coalescence of CAP coating during the curing process, the optimum packaging condition for the heat-humidity cured CAP coated beads was with desiccant to maintain the chemical stability of the CAP.

Cellulose↗

PubMed1998

Humidity-independent solid-state amperometric sensor for carbon monoxide based on an electrolyte prepared by sol-gel chemistry.

An amperometric sensor consisting of a film of silica gel over an interdigitated microsensor electrode provided a humidity-independent response to CO over the range of 9%-76% humidity. The residual solvent contents were in the 20%-50% range, depending on the age of the gels and the humidity. Variations in this range did not change the sensitivity. Gaseous CO was quantified in the absence of a contacting liquid phase using either linear scan voltammetry (LSV) or flow injection amperometry (FIamp) at constant applied potential. With LSV after a 2-min exposure to the sample, sensors with gels aged for 28-40 days yielded sensitivities of 0.38, 0.41, and 0.38 nA/ppmv for measurements at 9%, 33%, and 76% humidity, respectively; the corresponding correlation coefficients were 0.992, 0.995, and 0.999. The detection limit with FIamp was 5 ppmv.

Carbon Monoxide↗

PubMed2005

Characterization of the interaction between two food aroma components, alpha-pinene and ethyl butyrate, and ethylene-vinyl alcohol copolymer (EVOH) packaging films as a function of environmental humidity.

The ethylene-vinyl alcohol copolymers (EVOHs) are well-known high oxygen barrier materials that are being used successfully in the design of packaging structures for oxygen-sensitive food or pharmaceutical products. Recently, there has been increasing interest in using EVOH materials to provide a high barrier to organic compounds as a means to reduce food aroma scalping. However, the barrier function of this family of materials diminishes significantly in humid environments, and it is supposed that so does the organic vapor barrier. In this work, a new sorption-based method to characterize the interaction between food aroma and polymer films for packaging as a function of relative humidity is presented and is used to determine the barrier to ethyl butyrate and alpha-pinene of EVOH at 23 degrees C. The results show that although EVOH is an excellent barrier to food aroma when dry, a property that even improves at low relative humidity (RH), the solubility and diffusivity of the compounds tested increase dramatically with humidity at medium to high water activities. However, even in the worst case (100% RH), EVOH outperforms low-density polyethylene (LDPE) as a barrier to organic vapors at least 500,000-fold.

Bicyclic Monoterpenes↗

PubMed2002

Effects of relative humidity, temperature, and population density on production of cuticular hydrocarbons in housefly Musca domestica L.

The production of cuticular hydrocarbons by both males and females of Musca domestica L. under very wet conditions (90% relative humidity) compared to the production at 50 and 20% relative humidity is delayed up to at least 3 days after emergence from the pupae. Eight days after emergence, however, males contain the same amounts of hydrocarbons at 90, 50, and 20% relative humidity, whereas females at 90% still possess less of these substances than at 50 and 20%. It is suggested that this is due to the fact that males, being more active than females, need more cuticular hydrocarbons to prevent water loss. No indication is found that relative humidity has a different effect on the production of the sex pheromone, muscalure [(Z)-9-tricosene] by females than on the production of the other hydrocarbons. Male and female flies produce more hydrocarbons at 35 degrees C than at 20 degrees C. On females, the relative amounts of nonacosane and methyl- and dimethylnonacosanes are significantly higher at 35 degrees C than at 20 degrees C. Female flies produce some (Z)-9-tricosene after eight generations at low population density in contrast to females at high population density, which did not produce muscalure. We suggest that because of the relatively large contribution to the total population, the properties of a small number of females are likely to be expressed sooner in the next generations of small populations than in those of large populations.

Animals↗

PubMed2002

A laboratory evaluation of a regulated airflow through wheat at four combinations of temperature and humidity on the productivity of three species of stored product mites.

Aeration is a promising alternative to the use of pesticides for the control of storage insects by cooling bulk grain, but its effectiveness against mite pests is neither fully understood nor optimised. For this reason, the productivity of three species of storage mites, Acarus siro, Lepidoglyphus destructor and Tyrophagus longior, was studied in a laboratory-based experiment at four combinations of temperature and humidity (10 degrees C and 70% RH, 10 degrees C and 80% RH, 20 degrees C and 70% RH, 20 degrees C and 80% RH) with and without an airflow (at 10 m3/h/tonne, equalling 2.5 1/s/tonne, in tubes containing 15 g of grain). This is the first time that a study has examined the three principal components of aeration separately from each other. The effect of these factors was different for each species. For A. siro, temperature was the most important factor, while airflow and humidity were of similar but lesser importance. For T. longior, temperature was more important than humidity, while the reverse was true for L. destructor. For these two species, airflow was the least important factor. The airflow decreased the productivity of L. destructor and T. longior but increased the productivity of A. siro. This increase in productivity confirms that, in practice, prevention of mite infestations, in particular A. siro, will require storage of grain at low temperature, relative humidity and moisture content.

Acaridae↗

PubMed2002

The effect of structures on indoor humidity--possibility to improve comfort and perceived air quality.

The research presented in this paper shows that moisture transfer between indoor air and hygroscopic building structures can generally improve indoor humidity conditions. This is important because the literature shows that indoor humidity has a significant effect on occupant comfort, perceived air quality (PAQ), occupant health, building durability, material emissions, and energy consumption. Therefore, it appears possible to improve the quality of life of occupants when appropriately applying hygroscopic wood-based materials. The paper concentrates on the numerical investigation of a bedroom in a wooden building located in four European countries (Finland, Belgium, Germany, and Italy). The results show that moisture transfer between indoor air and the hygroscopic structure significantly reduces the peak indoor humidity. Based on correlations from the literature, which quantify the effect of temperature and humidity on comfort and PAQ for sedentary adults, hygroscopic structures can improve indoor comfort and air quality. In all the investigated climates, it is possible to improve the indoor conditions such that, as many as 10 more people of 100 are satisfied with the thermal comfort conditions (warm respiratory comfort) at the end of occupation. Similarly, the percent dissatisfied with PAQ can be 25% lower in the morning when permeable and hygroscopic structures are applied.

Adult↗

PubMed2006

Field performance of a nephelometer in rural kitchens: effects of high humidity excursions and correlations to gravimetric analyses.

Rural kitchens of solid-fuel burning households constitute the microenvironment responsible for the majority of human exposures to health-damaging air pollutants, particularly respirable particles and carbon monoxide. Portable nephelometers facilitate cheaper, more precise, time-resolved characterization of particles in rural homes than are attainable by gravitational methods alone. However, field performance of nephelometers must contend with aerosols that are highly variable in terms of chemical content, size, and relative humidity. Previous field validations of nephelometer performance in residential settings explore relatively low particle concentrations, with the vast majority of 24-h average gravitational PM2.5 concentrations falling below 40 microg/m3. We investigate relationships between 24-h gravitational particle measurements and nephelometric data logged by the personal DataRAM (pDR) in highly polluted rural Chinese kitchens, where gravitationally determined 24-h average respirable particle concentrations were as high as 700 microg/m3. We find that where relative humidity remained below 95%, nephelometric response was strongly linear despite complex mixtures of aerosols and variable ambient conditions. Where 95% relative humidity was exceeded for even a brief duration, nephelometrically determined 24-h mean particle concentrations were nonsystematically distorted relative to gravitational data, and neither concurrent relative humidity measurements nor use of robust statistical measures of central tendency offered means of correction. This nonsystematic distortion is particularly problematic for rural exposure assessment studies, which emphasize upper quantiles of time-resolved particle measurements within 24-h samples. Precise, accurate interpretation of nephelometrically resolved short-term particle concentrations requires calibration based on short-term gravitational sampling.

Air Pollution, Indoor↗

PubMed2002

Effects of cool and hot humid environmental conditions on neuroendocrine responses of horses to treadmill exercise.

To determine the effects of exercise, high heat and humidity and acclimation on plasma adrenaline, noradrenaline, beta-endorphin and cortisol concentrations, five horses performed a competition exercise test (CET; designed to simulate the speed and endurance test of a three-day event) in cool dry (CD) (20 degrees C/40% RH) and hot humid (30 degrees C/80% RH) conditions before (pre-acclimation) and after (post-acclimation) a 15 day period of humid heat acclimation. Plasma adrenaline and noradrenaline concentrations pre-acclimation were significantly increased compared with exercise in the CD trial at the end of Phases C (P<0.05) and D (P<0.05 and P<0.01, respectively) and at 2 min recovery (P<0.01), with adrenaline concentrations still elevated after 5 min of recovery (P<0.001). Plasma beta-endorphin concentrations were increased at the end of Phases C (P<0.05) and X (P<0.01) and at 5 and 30 min recovery (P<0.05) in the pre-acclimation session. Plasma cortisol concentrations were elevated after the initial warm up period pre-acclimation (P<0.01) and at the end of Phase C (P<0.05), compared with the CD trial. A 15 day period of acclimation significantly increased plasma adrenaline concentrations at 2 min recovery (P<0.001) and plasma cortisol concentration at the end of Phase B (P<0.01) compared with pre-acclimation. Acclimation did not significantly influence noradrenaline or beta-endorphin responses to exercise, although there was a trend for plasma beta-endorphin to be lower at the end of Phases C and X and after 30 min recovery compared with pre-acclimation. Plasma adrenaline, noradrenaline, beta-endorphin and cortisol concentrations were increased by exercise in cool dry conditions and were further increased by the same exercise in hot humid conditions. Exercise responses post-acclimation suggest that adrenaline and noradrenaline may play a role in the adaptation of horses to thermal stress and that changes in plasma beta-endorphin concentrations could be used as a sensitive indicator of thermal tolerance before and after acclimation. The use of plasma cortisol as a specific indicator of heat stress and thermal tolerance before or after acclimation in exercising horses appears limited.

Acclimatization↗

PubMed2006

Effect of an acute hot and dry exposure in moderately warm and humid environment on muscle performance at different times of day.

This study investigated whether 30 min of acute hot exposure has an additional passive warm-up effect for the improvement in muscle performance in a moderately warm and humid environment. We also sought to determine whether this effect is dependent on the diurnal variation in body temperature. Nine male subjects (age: 31.9 [+/- 5] years, height: 177 [+/- 6] cm, body mass: 69.3 [+/- 10] kg) were tested (CMJ, cycling sprints, and isokinetic contractions of the knee flexors and extensors) in a moderately warm and humid environment (24 [+/- 1] degrees C and 70 [+/- 4] % rh) with and without acute heat exposure (30 min of rest in a sauna at 76 [+/- 2] degrees C and 27 [+/- 1] % rh), both in the morning (07:00 - 09:00 h) and in the evening (17:00 - 19:00 h). Our results indicated a significant effect of both time-of-day and acute heat exposure on leg skin temperature (p < 0.01) but failed to show any effect of time-of-day or acute heat exposure on the various evaluated parameters (CMJ: speed, force, power and height; cycling power: over a half pedal revolution and a total pedal revolution; isokinetic torque: knee extensor and flexor muscles at 4.19 rad x s (-1), 3.14 rad x s (-1), 2.09 rad x s (-1), and 1.05 rad x s (-1)). In conclusion, our data suggest that 30 min of acute hot exposure does not have any passive warm-up effect in a moderately warm and humid environment. Furthermore, the diurnal variation in body temperature has no passive warm-up effect in a moderately warm and humid or in an extremely hot environment.

Adult↗

PubMed2003

Nasal mucosal temperature after exposure to cold, dry air and hot, humid air.

OBJECTIVE: To determine the influence of variations in the temperature and humidity of inhaled air on the nasal mucosal temperature at various sites in the nasal airways. MATERIAL AND METHODS: Fifteen volunteers were enrolled in the study. The temperature was measured on the mucosal surface of the nasal septum at the level of the nasal vestibule, in the nasal valve area, anterior turbinate area and choanae. Temperature measurements were made using a miniaturized thermocouple. Continuous temperature readings were performed before and after 10 min of exposure to either cold, dry air, ambient air or hot, humid air. RESULTS: Inhalation of cold, dry air significantly reduced the temperature of the septal mucosa at each location of measurement compared to the breathing of ambient air. Inhalation of hot, humid air significantly increased the septal mucosal temperature at all detection sites CONCLUSIONS: The climatic condition of inhaled air can lead to significant changes in nasal mucosal temperature. As the nasal mucosa is important for nasal air conditioning, short-term exposure to air of extreme temperature and humidity can rapidly compromise nasal air conditioning.

Adult↗

PubMedDate not supplied

Humidity control of an incubator using the microcontroller-based active humidifier system employing an ultrasonic nebulizer.

Relative humidity levels of an incubator were measured and controlled. An ultrasonic nebulizer system as an active humidifier was used to humidify the incubator environment. An integrated circuit-type humidity sensor was used to measure the humidity level of the incubator environment. Measurement and control processes were achieved by a PIC microcontroller. The high-performance and high-speed PIC provided the flexibility of the system. The developed system can be used effectively for the intensive care of newborns and/or premature babies. Since the humidifier generates an aerosol in ambient conditions, it is possible to provide the high relative humidity level for therapeutic and diagnostic purposes in medicine.

Biomedical Engineering↗

PubMed2002

An evaluation of ventilation system flow rates and levels of carbon dioxide, ambient temperature, and relative humidity in restaurants.

Studies of the indoor air quality of restaurants have rarely focused on ventilation system performance in relation to air pollutants and climatic factors. This study was conducted in eight restaurants to examine this issue by determining the ventilation flow rates and the levels of carbon dioxide (CO2), ambient temperature, and relative humidity during at least one complete shift of serving a meal. The mean values of number of dining patrons, ventilation flow rates, and the levels of CO2, ambient temperature, and relative humidity were not significantly different in the nonsmoking dining rooms and the smoking dining rooms. The mean ventilation flow rates in individual restaurants ranged from 42-113 cubic feet per minute per person (cfm/person), overall exceeding the recommended lower limit of 30 cfm/person. The mean levels of CO2 in two restaurants (646 and 819 ppm) were below, and in the other six restaurants (ranging 1,012-1,820 ppm) were above the recommended upper limit of 1000 ppm. The levels of CO2 in each restaurant significantly correlated with the number of dining patrons and in four restaurants accumulated gradually over time. In the nonsmoking dining rooms, the levels of CO2 increased significantly as the ventilation How rates decreased. The mean ambient temperature in restaurants (ranging from 22 degrees C - 24 degrees C) were within the recommended range of 20 degrees C - 26 degrees C. The mean relative humidity in six restaurants (ranging from 46%-59%) were within the recommended upper limit of 60 percent, and in two restaurants (62% and 71%) were slightly higher than this recommended limit. It was concluded that although the mean ventilation flow rates in all restaurants exceeded the recommended value, the design of the ventilation system or the distribution of air flow rate in some sections of restaurants were not appropriate to keep the levels of CO2 and relative humidity at some measurement locations below the recommended limits.

Air Pollution, Indoor↗

PubMed1985

Effects of air temperatures and humidities on efficiencies and lifetimes of air-purifying chemical respirator cartridges tested against methyl iodide.

Methyl iodide penetration curves through three types of respirator cartridges and canisters were determined at several temperatures to identify the significance of temperatures of testing and use. Three charcoal types showed similar results: triethylenediamine (5% TEDA-impregnated, (2% TEDA + 5% KI3)-impregnated, and unimpregnated. Penetration curves were shifted at higher temperatures in the range 25-38 degrees C, keeping relative humidity constant in the range 50-70%, but allowing absolute humidities to increase correspondingly. These shifts were such that penetrations were increased and service lives were decreased significantly (4-15% per degrees C). At constant water vapor concentration, service life of the (2% TEDA + 5% KI3)-impregnated charcoal increased with temperature, illustrating the complexity of temperature effects. For one case (5% TEDA) using cartridges at humidity equilibrium, temperature and humidity effects were sorted out. Until these effects are better understood, air-purifying respirator cartridge and canister testing should be done at conditions more representative of possible use and at more closely controlled temperatures.

Humidity↗

PubMed1987

The effect of temperature and humidity levels in a protective mask on user acceptability during exercise.

Subjective and physiological responses were obtained from six subjects wearing a ventilated face mask while exercising (3.8 met) for 15 min on a bicycle ergometer. Different combinations of ambient air temperatures (7 degrees, 16 degrees, 25 degrees C) and mask air temperatures (22 degrees, 27 degrees, 33 degrees C) were studied together with two different air humidities inside the mask (61% and 86% RH). Control experiments were performed without the mask at the same ambient temperatures. Skin temperatures, heart rates and skin wettedness were monitored during exercise. The subject's acceptance of the mask and thermal environment, thermal sensation, sensations of discomfort, sweating and skin wettedness, and their judgment of the work of breathing were assessed at the end of the 15 min exercise period. The acceptance of both the ambient thermal environment and of the thermal microclimate in the mask primarily was determined by the ambient air temperature, but it was influenced by the air temperature and humidity inside the mask. At ambient temperatures of 7 degrees C and 25 degrees C, the acceptance of the thermal work conditions decreased. In the warm environment a mask air temperature less than or equal to 27 degrees C was 100% acceptable and increased the acceptance of thermal environment. In the cool environment, a mask air temperature greater than or equal to 27 degrees C was 100% acceptable. The humidity content of the mask air was only important when the mask air was warm. Warm humid air significantly decreased acceptance of the mask conditions.

Adult↗

PubMed1987

Calculation of the performance of activated carbon at high relative humidities.

The Dubinin-Radushkevich potential theory was extended to include a term giving the effect of relative humidity on the uptake of adsorbate. This extended equation permits the adsorptive capacity of the activated charcoal in a respirator cartridge to be estimated for any combination of temperature, relative humidity, and concentration of contaminant. Application of this theory to previously published data of Werner showed a good correlation between theory and experiment. This equation is consistent with the experimental observations that 1) below a certain value, the relative humidity has little effect on the uptake of adsorbate, and 2) the effect of relative humidity, if observed, is more severe for lower than for higher concentrations of contaminant.

Adsorption↗