Wetting environmental pollution effects

Atmospheric corrosion of zinc is roughly proportional to the time of wetness in a particular location, a point emphasized by Mikhailovskii et al. (1986) for areas of the former Soviet Union, provided the nature and quantity of environmental pollution do not change a high relative humidity, which can cause condensation, increases corrosion. Rain obviously increases time of wetness, but it can have an indirect beneficial effect by removing corrosive materials. In practice, time of wetness is often taken as the time when relative humidity (RH) exceeds 80% and the temperature is above 0°C. Thin layers of solutions (except acids) are more corrosive than bulk solutions (Mansfield and Tsai, 1979). The general consensus is that the significance of atmospheric humidity in the corrosion of zinc is related to the conditions that may cause condensation of moisture on the metal surface and to the frequency and duration of the moisture contact. 

Phenol, a common priority pollutant, was extracted from two environmental matrices, soil and water, using near critical and supercritical carbon dioxide. The primary objective of this study was to determine the distribution of the contaminant between the soil or water and the supercritical phase, and the effect of soil moisture and co-solvents on the distribution coefficients. Static equilibrium extractions were performed on dry and wetted soil contaminated with 1 wt.% phenol and on water containing 6.8 wt.% phenol. Supercritical carbon dioxide (with and without en-trainers) was chosen as the solvent for the study. An appropriate entrainer for dry soil extractions (methanol) ffiffered from that found for aqueous extractions (benzene). However, soil moisture was found to have a significant impact on the effectiveness of en-trainers for soil extractions of phenol. Entrainers appropriate for extracting wetted soil were found to be the same as those advantageous for aqueous extractions. Benzene was also extracted from dry and wetted soil to investigate the extractability of a hydrophobic compound. 

Annual sulfate and other pollutant deposition needs to be proportioned on the basis of that attributable to wet and dry processes. While the long term effects of these different mechanisms may be similarly expressed as excess environmental loading by sulfate, the short term effects are known to be different. It is likely that in large areas of northeastern United States vegetation is continuously exposed to sulfate aerosol concentrations that are 3 to 5 times those found in remote regions of the U.S. 

Pollutants are removed from the atmosphere by rain and snow and are transferred to soils, natural waters, and vegetation by wet and dry deposition processes. Through these processes, plants are exposed periodically to substances dissolved in atmospheric precipitation and to gaseous pollutants. The major soluble constituents in rain and snow in the eastern U.S. are hydrogen, sulfate, and nitrate ions and there is concern over the environmental influence of these substances, particularly acidity (Jacobson et al., 1976). Knowledge of plant nutrition and response to pollutants raises the question of whether it is necessary to consider the supply of nitrate and sulfate in rain and the concentration of ozone in the atmosphere when determinations are made of the effects of acidic precipitation on vegetation of the eastern U.S. 

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