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average concentrations (divided into summer and winter periods) for the years 1960/61,
1961/62 and, as far as possible, for 1962/63. Both smoke and sulphur dioxide figures
for 1961/62 showed a reduction (about 10%) on the previous year. The results for the
summer of 1962 are about the same as in 1961. Table No.II shows the highest daily
average concentrations for the same periods as Table No.I. It will be noted that a
sulphur dioxide reading of 3,437 microgrammes per cubic metre is shown as the highest
daily average for December, 1962. This figure is, in fact, the highest recorded since
observations began in March, 1950, and is about 10 times the normal figure at this time
of year. It occurred on 5th December, 1962 during a period of persistent fog. The
corresponding smoke figure on the same day was, however, relatively low (880 microgrammes
per cubic metre), compared with results recorded during periods of fog in 1952
and 1957 (about 2,000 microgrammes per cubic metre). This reduction in the smoke content
of the fogs of 1952 and 1962 is illustrated in the reproductions of the filter papers
for 8th December, 1952 and 5th December, 1962, shown at Plates No.I and IIwhich follows.
For the purpose of comparison a filter paper for an average December day (14.12.61)
when there was no fog is shown (Plate No.3). The filter papers are those used in the
volumetric apparatus used for the measurement of air pollution; a measured quantity of
air is drawn through the filter upon which particles are collected and the darkness of
the resulting stain is related to the weight of smoke on the filter. A reflectometer
(a photo-electric device) measures the light reflected from the stain as a percentage
of that reflected from a clean filter. A formula is then applied to determine the
amount of smoke in the air.
PLATE NO.1
Filter Paper for
5th December, 1962. (fog)
PLATE No.2
Filter Paper for
8th December, 1952. (fog)
PLATE No.3
Filter Paper for 14th December, 1961.(no fog)
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