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pollution. This pollution consisting mainly of very fine particles, remains suspended in the air for a
long time and is often carried down wind for several miles. The inference is clearly that atmospheric
pollution is more than a local or even a regional problem, but a national one. A single community,
be it town or city, cannot obtain for itself a truly clean atmosphere since it is at the mercy of other
communities some of which may be quite remote from it. This does not mean that no benefit will
come from abatement of local pollution. The high concentration of pollution in an urban centre
before its own smokes becomes disseminated is, of course, far worse than the widely .distributed
general pollution.
The apparatus in use at Golden Lane is the standard equipment adopted by the Department of
Scientific and Industrial Research for measuring the concentration of suspended matter in the air.
With the aid of a small electrically driven pump, air from outside the building is drawn through a
filter paper at the rate of about 50 cubic feet per day, the volume being measured by a gas meter.
Each period of collection lasts 24 hours. The solid particles from the air are collected on the filter
paper and form a uniform circular stain one inch in diameter. The weight of pollution is estimated
by visual comparison of the stain with a standard scale of shades. By this means the shade intensity
is determined and then converted to an estimate of smoke concentration measured in milligrams per
cubic metre of air.
The mean monthly concentration of suspended matter in the air at Golden Lane during 1949
was 10.15 milligrams per cubic metre. Corresponding figures for other places in Great Britain where
similar observations are made are as follows: Birmingham 30.30, County Hall, London, 31.50, Rye
0.018, Salford 64.83. The station at Salford is situated in a densely populated district in which there
is also a considerable amount of manufacturing being carried on. At the other extreme the instrument
at Rye is situated at a R.A.F. Station in oper. country.
The mean monthly variation in suspended matter at Golden Lane and the other stations used
for comparison purposes is shown graphically in Figure 2.
FIG.2. MONTHLY VARIATION OF SUSPENDED IMPURITY. 1949.
SMOKE FILTER METHOD
Sulphur Dioxide.
The extent of atmospheric pollution due to sulphur dioxide may be measured in two ways. In
one method the absolute concentration of sulphur dioxide in the air, in parts per million or other,
convenient, unit, is obtained, whereas the second method provides arbitrary comparative values
which can be used for comparing the relative concentrations of sulphur dioxide in different areas.
Both methods are used in the City of London.