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98
The instruments at Kingston Guildhall and in Maiden Road, New
Maiden have been operating continuously since January 1958 and it is now
possible to obtain some indication of pollution trends at these two sites.
It is necessary to point out that variations in weather have a much
greater effect upon the daily readings than the factors which are more
important in relation to any real reduction of air pollution, such as
the changes in fuel usage and the increase in the efficiency of fuelburning
appliances. The weather can affect readings in two ways,
firstly, in colder weather more fuel is burned and more pollution is
caused; secondly, in calm conditions pollutants are liable to build up
in the air near their source, whereas windy weather causes dispersal.
An attempt has been made to assess the extent of the first of these
effects by the use of "Degree Days". Degree day figures are issued by
the Gas Council for checking and computing fuel consumption in central
heating systems. One "degree day" represents a difference of 1 F„
between the outside temperature and 60 F. maintained for one day of
24 hours, when the outside temperature is less than 60 The total
degree days in a month or a heating season are calculated by the Gas
Council from maximum and minimum temperature readings taken at Kew and
other observatories as supplied to them by the Meteorological Office,,
The annual figures for "degree days" are plotted on the same graphs
as smoke and sulphur dioxide concentrations at Kingston Guildhall since
1958 (figure l). It will be seen that in most years average smoke and
sulphur dioxide concentrations followed average temperature changes fairly
closely, in other words, cold winters resulted in proportionately more
pollution than mild ones. This method of comparison makes it possible
to assess more accurately the trends in air pollution in spite of
weather differences from year to year. The graph shows that from 1963
onwards although the "degree day" figures were fairly steady,, the smoke
and sulphur dioxide concentrations fell markedly. It is reasonable to
infer from this that there has been a real reduction in air pollution in
recent years. It is noteworthy that the sulphur dioxide concentrations
at the Guildhall site fell from 138 microgrammes per cubic metre in
1958/59 to 98 in 1965/66 and the smoke concentrations fell from 86 to 43
during the same period,, The figures from the Maiden site show a
similar pattern to those discussed above (Figure 2).
Figures 3 and 4 show the monthly variations in the smoke and
sulphur dioxide concentrations at the Tiffin Girls' School and the Alpha
Road, Surbiton sites. As in previous years the winter readings are
very much higher than the summer ones, indicating that domestic and
commercial space heating appliances contribute more to air pollution
than do industrial installations, most of which operate with a constant
level of flue gas emission throughout the year.