Atmospheric transparency over Qena/Egypt has been studied for direct solar radiation values, which were calculated from global and diffuse solar radiation measurements. The monthly mean of the instantaneously transparency coefficient has been analyzed in clear-, cloudy-, and mixed days. In general, the value of the transparency coefficient was found to decrease towards the sunset hours, owing to the high aerosol content expected in the afternoon time. The clouds deplete significantly the solar energy passed through them and then lead to an obvious decreasing in the transparency coefficient. A try to calculate the transparency coefficient has been done with the aid of the more available global solar radiation measurements. The results are in a good agreement with those obtained for direct solar radiation. The relation between the daily average of the transparency coefficient and the corresponding mean diffuse fraction has been investigated. High correlations were found between them in all months and empirical formulae were obtained.

Increasing mercury contents are reported from freshwater systems and fish in northern Europe and North America. Mercury input from soils is a major source with the leaching being affected by increased atmospheric mercury deposition compared to pre-industrial times and by other environmental conditions such as acid rain. The results of a mathematical model-calculation of vertical inorganic Hg(II) leaching in a Scandinavian iron-humus podzol under different atmospheric input rates of mercury are presented. Leaching under background rain conditions was calculated to be considerably stronger than under acid rain conditions. Increasing fractions of deposited soluble or solute atmospheric mercury were leached from the Of₍ₕ₎-horizon with decreasing soil content of soluble mercury under acid rain conditions; this effect was less pronounced under background rain conditions. The steady state concentrations of soluble mercury of the upper soil horizons were calculated and compared with the actual concentrations of total (= soluble + insoluble mercury) and extractable (= estimate of soluble) mercury measured in these horizons. The results indicate that even if the deposition of airborne mercury to soil is strongly reduced, the total mercury content of the soil decreases only slowly. It may take decades or even centuries before a new steady state concentration of total mercury is established in the soil. The decrease of the mercury concentration in the Of₍ₕ₎-horizon is probably largely dependent on the turnover of organic matter, binding most of the deposited airborne mercury in an insoluble form. Hence, present day mercury leaching is likely to be dominated by mercury deposited during former times and temporarily retained in an insoluble form in the organic matter.