Humidity, relative, impact

Fluctuations in the leaf environment are normal the exposed plant can not offer the degree of stability or moderation of extremes as can soil. Temperature, humidity (relative air humidity and free water), precipitation, radiation and wind speed have the greatest impact on the leaf microclimate (42-44). These factors can be modified by plant density and development, and by the growth of individual plant leaves and shoots (45-47). The influence of plant density in turn depends upon such factors as direction of the crop row relative to the prevailing wind, irrigation or precipitation, and the plant height (45). Increasing plant density tends to reduce the fluctuations in temperature and relative humidity, and to alter the distribution of dew. 

Relative humidity can have a significant impact on drying behavior and film quahty. Water-based formulations that perform weU when apphed under dry conditions may be deficient under high humidity apphcation conditions. The rate of water evaporation is much slower at high humidity, but solvent evaporation continues. This results in solvent depletion during the critical phases of film formation and consequent poor film development. 

Mass concentration units for ambient measurements are mass (/xg) per unit volume (m ). Size classification involves the use of specially designed inlet configurations, e.g., PMjq sampling. To determine mass concentration, all the particles are removed from a known volume of air and their total mass is measured. This removal is accomplished by two techniques, filtration and impaction, described in Chapter 13. Mass measurements are made by pre-and postweighing of filters or impaction surfaces. To account for the absorption of water vapor, the filters are generally equilibrated at standard conditions T = 20°C and 50% relative humidity). 

Figure 6.1 applies for a relative humidity of 50% however, in moderate environments the air humidity has only a modest impact on the thermal sensation. Typically, a 10% increase in relative humidity is experienced as equally warm as a 0.3 °C increase in operative temperature. 

For the above polyol blend viscosity (Brookfield, ASTM D-2196) = 1500 mPa-S at 23° C. For the reaction mixture working (pot) life 20 min Gardner circular dry times [72°F, 54% relative humidity (RH)] surface dry = 1.0 h, hard dry = 2.0 h, mar free = 3.5 h. For the finished coating gloss (ASTM D-523) = 90+ at 60° impact (ASTM D-2794) = 60 in.-lb direct, 10 in.-lb reverse Tabor abrasion (ASTMD-4060,1000 g load, 1000cycles, CS-17 wheel) = 95.6 mg pendulum hardness = 180 s MEK double rubs (ASTM D4752-95, 50 double rubs) = softened. 

Atmospheric aerosols have a direct impact on earth s radiation balance, fog formation and cloud physics, and visibility degradation as well as human health effect[l]. Both natural and anthropogenic sources contribute to the formation of ambient aerosol, which are composed mostly of sulfates, nitrates and ammoniums in either pure or mixed forms[2]. These inorganic salt aerosols are hygroscopic by nature and exhibit the properties of deliquescence and efflorescence in humid air. That is, relative humidity(RH) history and chemical composition determine whether atmospheric aerosols are liquid or solid. Aerosol physical state affects climate and environmental phenomena such as radiative transfer, visibility, and heterogeneous chemistry. Here we present a mathematical model that considers the relative humidity history and chemical composition dependence of deliquescence and efflorescence for describing the dynamic and transport behavior of ambient aerosols[3]. 

McQuain et al. (2003) undertook a detailed study on the effects of relative humidity and a direct comparison of fhe impacts DMSO vs. betaine in print buffer on the overall performance of quill pin printing. A video microscope was employed to visualize and track the drying behaviors of the various printing inks. A Cy5-labeled 466-bp dsDNA probe was used to monitor the printing process. Drop-drying behavior, bulk evaporation from the quill reservoir, surface tension changes, and spothng characteristics (spot diameter, spread, and number deposited) were examined at different RH levels. 

The effect of these two groups of parameters is linked, because contaminants need a given level of humidity to act on the corrosion process. A combination of contaminants could have different effects than the sum of the individual effects. In ISO 11844-1 [29] it is explained that the impact of temperature and relative humidity can not be expressed... 

Additional comments Relative humidity and air flow through the system must be controlled within specified limits. The test ring and test ball must be properly prepared before use. Improper preparation and contamination can impact test results. Relative humidity of air in the system must be greater than 30%. 

Haghighat, F., and L. de Beilis, Material Emission Rates Literature Review, and the Impact of Indoor Air Temperature and Relative Humidity, Bldg. Environ., 33, 261-277 (1998). 

Epidemics are most likely to occur when the climate provides the optimum combination of temperature and humidity or when animals are kept under crowded, damp conditions. The impact of a parasitic infection varies considerably according to the species of the worm involved. Adult tapeworms are relatively harmless, but certain blood- or tissue-feeding species of nematodes are highly pathogenic. More often than not, however, it is the invasion of the larvae rather than the adult parasites that is responsible for outbreaks of clinical disease. 

Camuffo, D. and Pagan, E. (2004) Impact of daily and seasonal temperature and relative humidity cycles on wooden artworks. 6th Indoor Air Quality 2004 Meeting... 

Relative humidity has the greatest impact on Ca(0H>2 reactivity. Figure 4 shows Ca(0H)2 conversion as a function of time at 19, 50 and 70% relative humidity. All three experiments were run at 2000 ppm inlet SO2 and 66° C using 4 g of lime 0. The discontinuous line in the figure corresponds to the Ca(0H)2 that would be converted if all the SO2 were being removed. For all relative humidities,... 

The other variables tested, i.e. temperature, amount of Ca(0H)2 and S02 concentration have a lower impact on the reaction rate. The different effect of S02 concentration at low and high relative humidity can be explained by assuming that the reaction has zero order kinetics in SO2 and that at low relative humidity the reaction rate is mass transfer controlled while at high relative humidities the reaction is controlled by reaction kinetics. 

Activated carbon is commonly acknowledged to be very efficient as a VOC adsorbent. However, in the last decade, interests arose to develop new materials, such as alumni-silicate molecular sieve, towards operating conditions for which activated carbon was inappropriate due to its inflammability and adsorption capacity dependence on effluent relative humidity. Apart from hydrophobicity, the advantages of High Silica Zeolites (HSZ) are notably a thermal and chemical stability, a high steric selectivity and a complete regeneration at low temperatures [11]. Yet, for adsorption and separation processes development, organic compounds properties impact on adsorption and crystalline framework influence on selectivity are to be clarified and efficiently modeled. 

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