The Anthropogenic Effects of Air Pollution Upon Soil, Terrestrial Vegetation and Materials and Building Facades
Adverse chemical impacting on soil and vegetation is due to dry deposition where the air is cleansed by direct absorption by plants and soil of air pollutants. Further cleansing is accomplished by washout and by rainout, the latter a cleansing of clouds and the former a removal of pollutants in the air beneath clouds by falling precipitation.
Soil is a hetero—colloidal mix of organic and inorganic matter stratified into horizons. Horizon “A” near the surface is where the weathering of inorganic material occurs and where biological organic matter decomposes. Horizon “B” beneath “A” receives the dissolved matter and minerals which percolates through. Themetallic compositions remain in equilibrium in the pH of the soil. Acid rain alters the pH in “A” horizon and subsequently in horizon “B” as well.
The equilibrium is maintained because under normal conditions weathering and gas extraction from the soil lead to the release of gases, whereas the litter (biotic decomposition) and atmospheric acid lead to acidification. Slow acidification called podsolization can be accelerated by leaching and increasing the rate of biotic matter decay. Interestingly, nutrient elements needed in the Soil are N, P, K, NA, Mg, S but soil contamination by toxic metals as a result of aerial deposition are Pb, Zn, Cu, Cd Ni and Hg. Atmospheric fluoride is phytotoxic at 25-50 ppm and aluminum is abundantly toxic in soils.
Some elements essential for plant growth and also injurious to plants in certain forms and concentrations are nitrogen and sulfur. Both are necessary for plant protein synthesis but deleterious in dry deposition and acid rain form. Additionally, acid precipitation impacts directly on plant foliage and by contributing to impoverished soil conditions and by destroying beneficial microorganisms.
Experimentation has produced quantitative and qualitative parameters of tolerance of polluting chemicals upon plant life. It has been determined that pollutants can plasmolyze cells and thereby destroy plant chlorophyll which then reduces plant food production.
Ozone causes tobacco leaves to develop light-colored lesions and pinto beans to develop stippled pigmentation.
PAN injuries are similar to other pollutants manifested by silvering or glazing of the leaf surface and the plasmolization of the parenchyma cells. It is noted experimentally, that varying the conditions of light intensity, temperature, humidity and nutrition alter the “threshold” of injury in most vegetative forms. For example, nitrogen dioxide at 55 ppm and SO2 at 3 ppm for 8 hours is sufficient to overcome the “injury threshold”.
The accumulative deleterious effect upon vegetation and other environmental problems depends on ‘local receptors’ for ethylene.