The proportions of two atmospheric gases, oxygen and carbon dioxide, are of critical importance for the support of life. Neither is thought to be in limiting supply even though carbon dioxide forms only 0.03 percent of the atmosphere by volume percentage. Stoker et. al., (1976) have explained that the general availability of C02, despite its small percentage occurrence, is due to the high mobility of carbon in the planetary cycling of this component.
Some fears have been expressed by Manable and Wetherall (1975) that the CO2 content of the atmosphere could increase due to the burning of fossil fuels by man and the consequent release of C02 to the atmosphere. This, in turn, could result in a warming of the lower atmosphere by 0.5°C by the year 2000 AD.
The chemistry of the media has been relatively constant probably for as long as 3.4 x 108 years (since Silurian times). From the early 1950s mankind’s increasing use of high temperature and high pressure combustion processes along with the use of increasingly complex chemical substances has led to a massive increase of air and water pollutants.
Sulphur dioxide, hydrogen sulphide and the nitrous oxide group of pollutants have become problem substances in the air over many of our industrialised conurbations. Hickey (1971) has started that conclusive proof about what is unhealthy about pollutants is often unclear. The controversy over the source, the effect and the hazardous nature of acid precipitation (Hutchinson et. al., 1980) is an example of the confusion which exists about the pollutants man has placed in the atmosphere.
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The water contained within the biosphere is also becoming contaminated by toxic chemical materials (McCaul, et. al., 1974). Natural, unpolluted precipitation should have a slightly acid pH of about 6.5 (pH 7.0 = neutral). Rain-water contaminated by oceanic spray or precipitation which occurs during ligthning stroms is usually more acidic (pH 6.0).
Mildly acid precipitation has some effect upon soil fertility in that the free hydrogen ions in the rainwater leach the chemical bases from the top layers of the soil. Only when this leaching process has continued for several thousands of years does evidence of soil nutrient exhaustion become evident.
The impact of man’s increasing trend towards industrialization has led to an intensification of atmospheric acidification so much so that rainwater pH over urban/industrialised areas may now attain pH 5.5 (Goudie, 1984). The variety of dissolved acids has also increased.
As a consequence, very acid precipitation can cause ‘bum’ marks on vegetation surfaces, can damage the vigour of plants and in extreme cases can cause the death of vegetation for example, Western Hemlock confiers (Tsuga heterophil la) planted on the Pennines in England (Hepting, 1964; Roberts et. ai, 1983).
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The chemistry of surface water bodies is further changed through the additional dumping of industrial and domestic wastes from which solutes migrate into rivers and lakes. The temperature of river waters can be raised by the addition of cooling waters from thermal power stations (Hodges, 1977).
Toxic Chemicals and Biosphere Catastrophes
We have so far averted a major change in the chemical composition of the atmosphere, not by any foresight on behalf of man, but by the ability of the atmosphere and hydrosphere to self-cleanse themselves of toxic materials. This is achieved mainly by the major cyclling of materials between ‘available’ and ‘non-available’ reservoirs (Strahler et. ai, 1974).
A number of localised catastrophes have occurred, for examples the Meuse Valley air pollution incident of 1930 and the smog which killed an estimated additional 4000 people in London 1952. The Los Angles problem and similar problems in Tokyo and Mexico City have produced well documented effects on human health (Report on Air Pollution, 1970; Stewart, 1979). The Council on Environmental Quality (1973) have calculated the cost of pollution damage in the U.S.A. By 1968 this figure was calculated at $16.2 billion of which $5.0 was credited to material and vegetation damage.