- 2128 =~ 
The light energy available for photosynthesis is also reduced by the blackening 
of leaves by dust particles. These are usually heavy and settle out of the 
atmosphere quite quickly. The problems and effects on vegetation, as observed 
on aerial photographs, thus tend to be fairly local, being most acute close to 
the source,then decreasing rapidly. The introduction of the Clean Air Ac* has, 
in the United Kingdom, reduced the amount of smoke emitted per year from 2.3 
million tons in 1953 to 0.6 million tons in 1975. The reduction of smoke is 
purely for aesthetic reasons to prevent the ubiquitous deposits of dust creating 
depressing scenes, as the damaging pollutant, sulphur dioxide, is nov removed 
by burning smokeless fuels. 
In 1972 Schneider reported of a project in the populated industrial aggloreration 
on the Lower Main River, near Frankfurt, West Germany. Several factors, including 
the continual construction of new industrial plants, rising number of pıivube cars, 
emission from chimeys etc., have led to rapidly decreasing air quality in the 
river basin between hilly ranges. Some 40% of the days in any year are windless, 
which leads to smog conditions. The only constant fresh circulation of re- 
generated air comes from the slopes of the Taunus Mountains. In order to 
determine local climatic conditions for the area, the Regional Planning Board 
for the Lower Main carried out a pilot study of air quality and meteorological 
measurements. Flights with an infra-red scanner and radiometer were made at 
various seasons of the year and correlations calculated for climate, emission 
and amount of air circulation. On the basis of these results, the remaining 
fresh air corridors were mapped and definitive plans drawn up for the preservation 
of these important oxygen rich veins for the city. The aim of the Planning 
Board is not only to prevent indiscriminant building acrose the remaining 
corridors, but also, to improve the air circulation by 'greening' the hill slopes. 
Ffficient regional planning measures of this type provide good environmental 
conditions in densely populated areas. 
Similar conditions were discovered during research into environmental damage to 
the Saar River, near Saarbrucken, West Germany. Infra-red line scanner imagery 
taken in the early morning showed fresh cold air i: side valleys, which could 
not flow down into the main river valley due to buildings or high forests on 
the slopes. 
2.9 Sulphur Dioxide 
Plants seem to be more susceptible to sulphur dioxide pollution than animals. 
levels between 0.1 and 1.0 parts per million (pp») have often been shown to cause 
obvious symptoms, such as leaf blotching and reduction in yield of crops. 
Coniferous trees grow poorly and even die in many urban or industrial areas. 
The group of plants most thoroughly studied is the lichens, many species of 
which are absent, because of their extreme sensitivity to sulphur dioxide. 
Species of lichens can be directly correlatec with the level of sulphur dioxide 
pollution and many studies have been reported on the zonation of urban areas 
vsing this method. - 
The degree of dispersion and dilution of sulphur dioxide is related to various 
factors, such as climatic conditions and the height of the emitting cbinmey. 
Depending on its concentration, the season and other climatic factors, the 
harmful effects of sulphur dioxide range from retardation of growth and exposure 
io death by poisoning. Susceptibility also varies with species, stage of growth 
and exposure time as well as being affected by environmental factors of air 
temperature, humidity, light invensity ana water supply. 
Although chronic damage of vegetation cauced by sulphur dioxide fumes is 
invisible to the naked eye, its effects «an be determined on colour infra-red 
aerial photography. As the pollutant affects the pigments (chlorophyli a and b) 
there is a loss of reflectance in the infra-red wavelengths. In gen?ral, the 
reddish photographic rendition of healthy trees and vegetation grades into magenta, 
purple and green as the loss of infra-red reflectance progresses. This has 
been reported by Dargie(1975), van Genderen(1974), Kirby(1977), Myers(197^), 
Olsen (1971), Remeyn(1972), Stellingwerf (1969), Sukhih and Sinitsin(1974), 
Weber and Polcyn(1972).