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49
sulphur dioxide was less in six of the ten months. The average
concentration of smoke for the ten months ended December, 1950,
was 21.6 milligrams per 100 cubic metres, whilst the figure for the
same period in 1951 was 19.6. This amounts to a reduction in
smoke pollution of 9.3 per cent. A reduction in the average
concentration of sulphur dioxide also occurred, amounting to
7.5 per cent. It is probable that the reduced pollution was largely
attributable to weather conditions. The sulphur dioxide figures
for July and August, 1951, had to be estimated owing to a fault
in the apparatus which affected the results.
An alternative method of measuring the amount of sulphur
dioxide in the air is by the exposure of a cylinder coated with lead
peroxide, a material which readily absorbs sulphur dioxide. In
order to assist the Department of Scientific and Industrial Research
in its examination of this method, a lead-peroxide instrument was
installed early in 1951 in close proximity to the existing inlet point
of the volumetric apparatus at Sidmouth Road, Leyton, thereby
enabling a comparison of the two methods to be made. The instrument
was provided and is maintained by the Department of Scientific
and Industrial Research. Two other lead-peroxide instruments
have been installed in the Borough during the year; both are
situated in the Lea Bridge area.
The following graphs show the annual variations of smoke
and sulphur dioxide in Leyton compared with Central London:—